a theoretical analysis of how the protein and phosphorus...

Defra Project IS0208

FINAL REPORT

A theoretical analysis of how theprotein and phosphorus requirementsof livestock may best be met.

A report for Defra compiled by:

ADAS

B R CottrillR Sylvester-BradleyJ WebbSusan TwiningM Temple

IGER

Annette Longland

The University of Reading

L Crompton J Mills

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Contents

Section 1: Introduction................................................................................................................................4Section 2: Environmental effects of N and P excretion by farm livestock....................................5

Loses of N and P from agricultural soils..............................................................................................6 Nitrogen........................................................................................................................................6 Phosphorus..................................................................................................................................7The need for biodiversity in UK grassland......................................................................................7

Section 3: Livestock numbers and their requirements for N and P................................................9 Livestock numbers..........................................................................................................................9 Livestock requirements for nitrogen and phosphorus.............................................................11 The supply of nitrogen and phosphorus from feeds................................................................12

Section 4: Feeds for livestock.................................................................................................................13 Forages..........................................................................................................................................13 Concentrate and compound feeds.............................................................................................14 Summary of N and P demand and supply................................................................................16

Section 5: Forages – Optimising N utilisation....................................................................................18(i) Plant breeding and conservation...................................................................................................18(ii) Forage selection, management and supplementation..............................................................20

Grass..........................................................................................................................................21 Forage maize and maize silage..............................................................................................21 Forage legumes........................................................................................................................22

Fertiliser used to achieve home-produced inputs....................................................................23Section 6: Concentrate feed selection and management................................................................25

Cereals...........................................................................................................................................25 Rapeseed meal.............................................................................................................................29 Peas and Beans............................................................................................................................29 Linseed meal.................................................................................................................................30 Lupins.............................................................................................................................................30

Section 7: Feed selection and management strategies...................................................................32 Pigs and poultry............................................................................................................................32 Ruminants......................................................................................................................................33

Feeding according to protein requirements..........................................................................34 Substitution of grass silage with alternative forages...........................................................34 Supplementation with synthetic amino acids........................................................................35 Diet supplementation with readily fermentable carbohydrate............................................36

Section 8: Scenarios for improving dietary N utilisation by livestock.........................................37(i): Scenarios for improving dietary N utilisation by pigs and poultry................................................37

(a) Using an ideal protein approach...............................................................................................37(b) Replacing wheat with maize......................................................................................................37(c) The Low N Grain concept..........................................................................................................38(d) Discussion....................................................................................................................................39

(ii) Scenarios for improving dietary N utilisation by dairy cows.........................................................40(a) Reducing N intake......................................................................................................................40(b) The effect of energy source on NUE.......................................................................................41(c) Changing the concentrate protein source...............................................................................41(d) Using synthetic amino acids......................................................................................................42(e) Synchronising energy and protein supply to rumen micro-organisms...............................42(f) Use of alternative forages – forage maize...............................................................................43(g) Use of alternative forages – sugar grass................................................................................43(h) Adopting management strategies to increase NUE..............................................................44

(iii). Scenarios for improving the NUE of forage-fed sheep and beef cattle....................................44(a) Sheep finished on High Sugar grass (HSG)...........................................................................45(b) Beef finished on HSG.................................................................................................................45(c) Maize silage for beef cattle........................................................................................................46(d) Fertiliser: improved management and reductions in application.........................................47

(iv): Impact on N emissions.....................................................................................................................48

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(b) Dairy cows....................................................................................................................................50(v): Summary and conclusions...............................................................................................................51Dietary sources of phosphorus..........................................................................................................52Livestock P excretion and the environment....................................................................................52Meeting the phosphorus needs of livestock...................................................................................53

Requirements for Phosphorus....................................................................................................53 The bioavailability of dietary phosphorus..................................................................................53

Strategies for improving P utilisation by farm livestock.............................................................541. Pigs and Poultry................................................................................................................................54

Feed processing............................................................................................................................54 Selection of feeds with higher P availability..............................................................................54 Use of exogenous enzymes........................................................................................................55 Diet supplementation with inorganic P......................................................................................56 Reducing dietary P concentrations............................................................................................56 Livestock breeding........................................................................................................................57

2. Ruminants...........................................................................................................................................57 Assumptions on the availability of dietary P.............................................................................58 Use of exogenous phytases........................................................................................................58 Reducing levels of supplementary P.........................................................................................58

Section 10: Indicators of nutritional adequacy..................................................................................62Section 11: Discussion and Conclusions............................................................................................63

Given this range of efficiencies, it is clear that there is scope for further improvements in N and P utilisation.................................................................................................................................63 Nitrogen.....................................................................................................................................64 Phosphorus..............................................................................................................................66

Appendices..................................................................................................................................................85Appendix 1. Defra-funded studies that have addressed issues related to this project include:. 85Appendix 2. The calculation of protein and phosphorus requirements..........................................86Appendix 3: Raw material usage in the production of animal feedingstuffs in Great Britain in 2002, and estimated supply of nitrogen (N) and phosphorus (P) ('000 tonnes).............................87Appendix 4: UK imports of Animal Feedingstuffs (‘000 tonnes): average per year for the period 1998 - 2000................................................................................................................................................88Appendix 5. Area of British grassland by class type........................................................................89Appendix 6. Estimated annual dry matter (DM) yields from British Grasslands...........................90Appendix 7. Estimated annual N yield from British grassland.......................................................91Appendix 8. Estimated annual P yield from British grassland........................................................92Appendix 9. Estimated DM, N and P production from conserved forages in GB in 2002..........93Appendix 10. Theoretical reductions in N loss from ewes and lambs on ‘high sugar’ grass (HSG) compared with conventional (CG) ryegrass swards*..............................................................94Appendix 11. Theoretical reduction in N loss from feeding finishing beef steers on high sugar grass (HSG) a control grass (CG) or permanent pasture (PP).........................................................95Appendix 12. Theoretical reductions in N ‘loss’ to the environment from the 2002 beef herd from grazing High Sugar Grass (HSG) vs. Permanent pastures (PP).............................................96Appendix 13. Theoretical reductions in excess supply of N to the 2002 UK beef herd, when high sugar grass (HSG) sward was grazed vs. permanent pasture (PP)........................................97Appendix 14.. Theoretical reductions in N loss from the 2002 UK beef herd, when grass silage (GS) was substituted with 33, 67 or 100 % Maize silage (maize silage) when offered to finishing beef steers (424-570kg) or to the remaining beef-herd for 180d......................................................98Appendix 15. Theoretical reductions in excess supply of N to the 2002 UK beef herd, when grass silage is substituted with maize silage........................................................................................99Appendix 16. Annual N balances for arable and forage crops in the UK....................................101

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Section 1: Introduction

It is widely accepted that dietary nitrogen (N) and phosphorus (P) are poorly utilised by livestock. The low efficiency with which N is converted to animal products (milk, meat or eggs) is due to the unavoidable losses associated with digestion, metabolism, growth and inherent inefficiency of converting plant protein to animal protein, made worse by an imbalance between amino acid requirements and supply. For P, the low utilisation – particularly by pigs and poultry - is largely due to the fact that much of the P in vegetable feeds is stored in a form (phytate P), which they are unable to digest. The result of this poor utilisation is that N and P are excreted in manure, with adverse environmental consequences. Manure and slurry from farm livestock are a major source of environmental pollution, particularly in terms of ammonia (NH3) volatilised to the air, nitrate leached to ground water, N and P run-off to surface water and methane (CH4) emissions.

The main objective of the project was to identify strategies for to maximise the utilisation of dietary N by farm livestock and poultry and analyse the economic and environmental implications of so doing. Phosphorus was also considered. This was achieved by addressing the following sub-objectives:

To compare the supply of N and P with requirements, characterising the environmental consequences of any oversupply.

To evaluate the scope for minimising N or P surpluses by changes in cropping and fertiliser use, livestock nutrition and/or the amount of imported or manufactured feeds.

To evaluate the scenarios identified, assessing their impact on emissions, land use, biodiversity and economics.

To identify likely trends in livestock numbers and, using nutritional models, evaluate how these changes may affect N and P requirements.

To identify the environmental and economic effect of these changes on the different feeding systems, management and cropping scenarios identified above.

To make an economic assessment of the scenarios identified, and their potential uptake by the industry.

The research used extant models of livestock systems, scientific literature and recent Defra-funded reports to derive quantitative or semi-quantitative estimates of N and P fluxes in current livestock systems, and then to estimate likely impacts on those fluxes of alterations to livestock production.

In doing this, consideration has been given to the current environmental impact of farm livestock, and the economic and environmental implications of alternative strategies for meeting these requirements. A number of Defra-funded studies, listed in Appendix 1, have already considered a number of the issues related to these aims.

Throughout this report, references are made to the efficiency with which livestock utilise dietary N and P. In most cases efficiency is simply calculated as nutrient in product output/nutrient in feed intake. These are, in fact, estimates of apparent utilisation. Before production can occur, animals require nutrients for maintenance and for reproduction. Requirements for these processes have a high priority, but are distinctly different from those needed for production. It has been estimated that an animal requires about 10% of the energy to be presented as N containing amino acids to support basic and essential metabolism, whereas production of lean meat requires no less than 35% of the energy to be supplied as amino acids (Tamminga, 2003). The true efficiency of production, i.e. the requirement for production, is variable and poorly predictable, since under less efficient production systems amino acids may be oxidised and used as fuel, with N excreted in manure.

In order to establish the potential for change in the supply of protein and phosphorus to farm livestock for this report, 2002 was taken as the baseline, since this was the latest year for which full statistics were available at the start of the project. The initial intention was that this report would deal with livestock in England and Wales. However, feed data were not available for England and Wales alone and therefore, with the agreement of Defra, feed use and animal numbers refer to Great Britain, unless specified otherwise.

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The major part of this report deals with options for optimising N supply. The implications of inefficient use of dietary P and strategies to improve its utilisation are mainly discussed in Section 8 (page 52).

Section 2: Environmental effects of N and P excretion by farm livestock

Nitrogen lost from livestock excreta and manures may cause various forms of pollution. Soluble N compounds are quickly converted in soil to nitrate-N (NO3

-) which enters ground and surface waters following application of manures to land (Smith & Chambers, 1997) and from grazed pastures (Tyson et al., 1997). Around 29% of leached NO3

- is estimated to arise from livestock (Webb, 2000). Ammonia (NH3), when deposited to land increases N eutrophication and soil acidification (Roeloffs and Houdijk, 1991). Agriculture is estimated to produce 80-90% of European NH3 emissions (ECETOC, 1994). Non-agricultural emissions arise from a large number of relatively small sources (Sutton et al.,2000), and therefore the greatest reductions in NH3

emissions are likely to be achieved by reducing those from agriculture. Within agriculture, c. 80-90% of emissions arise from excreta produced by livestock (Misselbrook et al., 2000). Nitrous oxide (N2O) contributes to global warming (Bouwman, 1990) and breakdown of stratospheric ozone (Crutzen, 1981). Nitrous oxide and dinitrogen (N2) may be emitted from livestock housing (Groenenstein & van Fassen, 1997), during manure storage (Willers et al., 1996), following application of manures to land (Stevens & Laughlin, 1997) and from grazed pastures (Vermoesen et al., 1997). Livestock excreta and manures may also be an underestimated source of nitric oxide (NO) (Groenenstein & van Fassen, 1997; Watanabe et al., 1997). Only emissions of dinitrogen (N2) are environmentally benign. Losses of N2O, N2 and NO were estimated to be 13.3, 40.0 and 0.6 tonnes x 106 N, respectively (Webb, 2000). These represent c. 12 % of national emissions of N2O but <1% of national emissions of NO.

Agreements have been made to reduce N pollution from agriculture. The EU Nitrate Directive (EEC, 1991) requires member states to introduce measures to reduce NO3

- losses from soils. The 1999 Gothenburg Protocol sets targets to reduce emissions of atmospheric pollutants including NH3. As a result of the Kyoto protocol, the UK has agreed to a legally binding reduction of greenhouse gas emissions of 12.5 % of 1990 levels by the period 2008-12. The transfer of phosphorus (P) from agricultural land to watercourses contributes to eutrophication of rivers, estuaries and lakes. The P content of livestock manures is highly susceptible to transport to watercourses in runoff during heavy rainfall. The EU Water Framework Directive (EEC, 2000) requires reduction in emissions of hazardous materials to watercourses.

Not all of the N in excreta is readily lost. Much of the N in mammalian faeces is undigested or partially digested proteins that are mineralised only slowly (Van Fassen and Van Dyke, 1987). In contrast, the urine of mammals contains mainly urea (Jarvis et al., 1989) and other compounds that are readily hydrolysed to NH4 (Groot Koerkamp et al., 1998). Uric acid is a major constituent of poultry faeces (avians do not produce urine) and this, together with some other labile compounds, may be degraded to NH4 after hydrolysis to urea (Groot Koerkamp, 1994). Together these labile-N compounds in livestock excreta are referred to as total ammoniacal-N (TAN) and may be regarded as the source of almost all NH3 emissions. This TAN is also the major source, in the season following manure application and grazing, of NO3

- leaching (Smith & Chambers, 1997), and a significant source of N2O, N2 and NO emissions (Yamulki & Jarvis, 1997).

Diets for livestock are formulated to meet the nutrient requirements of the stock to which they are fed. Because of uncertainty over both the protein requirements of livestock the quality of the protein in the feeds (its degradability in the case of ruminant feeds, and amino acid content and digestibility in the case of non-ruminant feeds), diets are usually formulated to contain excess protein. Surplus protein-N is mainly excreted in the form of urea (uric acid in poultry) (cattle: Smits et al., 1995; pigs: Kay and Lee, 1997; poultry: Elwinger and Svensson, 1996), the major source of NH3 emissions from livestock excreta. Thus reductions in N excretion by livestock as a result of ensuring that feed does not contain excessive protein would be expected to lead to at least a pro-rata reduction in all forms of N pollution. Moreover, since surplus N is excreted mainly as urea (or uric acid), reducing surplus protein in the diet will give a disproportionately greater reduction in NH3 emissions (Smits et al., 1995; Kay and Lee, 1997).

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Loses of N and P from agricultural soils

Nitrogen

Uptake of N from grassland is influenced both by level of N application and season. When sward uptake of N is high, (i.e. during spring and late summer) then uptake of applied fertiliser N by swards may be ca. 80%, at rates of up to 3.5 kg N/ha/d. Conversely, if applied during the winter, uptake by the plant will be low (Figure 1). However, even the most timely fertiliser treatment will result in some loss of fertiliser N, especially at high rates of application. There are three main routes by which fertiliser N can be lost from the soil; volatilization of ammonium, leaching and denitrification of nitrate.

Figure 1. Seasonal variation of N uptake by intensively managed grass swards (kg N/ha/d) (adapted from Humphreys et al 2002).

0

0.5

1

1.5

2

2.5

3

3.5

4

Jan Feb Mar Apr May Jun Jul Aug Sept Oct Npv Dec

Volatilisation of ammonium occurs when it is converted to ammonia and lost to the atmosphere, from where it can be conveyed elsewhere to be subsequently dissolved in rainwater, re-converted to ammonium and pollute vulnerable habitats distant to its origin. Most of the N in cattle slurry is ammonium, and if applied under good drying conditions at the soil surface, most if not all, may be volatilised. Urine N is in the form of urea which, on contact with the ground, is converted to ammonium, substantial amounts of which are volatilised soon after voiding. Much of the remainder is denitrified or leached, and O’Connell et al., (2002, a, b) suggested that urinary N contributes little to N supply for sward production. N excreted in dung is more stable as significant amounts may be incorporated into soil OM to eventually contribute to soil mineral N. Thus any practise which leads to partitioning of N excretion away from urine to faeces is environmentally desirable.

Nitrate leaching occurs when rainfall washes nitrate down through the soil, and is greatest under conditions of low plant uptake and heavy rainfall, being especially severe on well-drained soils. The nitrate can be derived from a number of sources including N fertilisers and that derived from stands of legumes. Nitrate losses from agriculture are estimated to be about 34 kg/ha/year for England and Wales (Defra, 2001). This can lead to substantial amounts of nitrate in aquifers, and levels in drinking water exceeding 100 mg nitrate/L have been associated with meta-haemoglobin or blue blood syndrome in young children. The EU Nitrate Directive sets a maximum admissible concentration (MAC) of nitrate in drinking water of 50 mg nitrate/l. Furthermore, recent research has shown that nitrite and organic N can also leach into watercourses. Nitrite is highly toxic to fish, and as result a maximum level of 9 g/l has been recommended by the EU, yet 100 g/l have been recorded in a Devon river (Haygarth and Scolefield., 2003).

Denitrification is an important route for N loss from farmland. It occurs when topsoil becomes waterlogged, and the nitrate is denitrified by micro-organisms to N2 or N2O, a ‘greenhouse’ gas. Denitrification occurs throughout the year, especially when the soil is warm and wet. Agriculture is thought to account for 50% of the anthropogenic N2O emissions in the UK, and under the 1997 Kyoto Protocol EU countries are obliged to reduce N2O emissions by 8% from the 1990 level by 2012. The N2O-N emissions from agriculture in 1990 were calculated to be 53,000 t, with grassland, leached N plus re-deposited ammonia, animals and non-grass crops accounting for 44, 24,17 and 15% of the total, respectively. Of the grassland-associated emissions, fertiliser was

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responsible for 78% of these equating to 34% of the total agricultural emissions. By contrast, corresponding values for slurry, grazing returns and FYM accounted for 6, 3 and < 2 %, respectively (calculated from Brown and Jarvis, 2001). Furthermore, the financial cost of fertiliser loss through denitrification has been estimated to be £100 million, annually in the UK (Witty and Mytton, 2001). Clearly, reductions in fertiliser application have great potential for abatement of N2O emissions.

Phosphorus

Losses of insoluble P occur when soil or manure particles are eroded, these often being transported to watercourses, where the aquatic flora and fauna can use the P. Application of fertiliser just prior to storm discharges of water into rivers can result in the direct transfer of large amounts of P to watercourses from eroded topsoil (Defra, 2001). In addition, where soil P concentration is high, (>60mg available P /kg soil, ADAS index 4), P may be leached from the soil in sufficient quantities to cause water quality problems. This is particularly the case under conditions of rapid alternation between wet and dry conditions (Haygarth and Scholefield . 2003). In bodies of fresh water where the P levels are excessive, eutrophication occurs, resulting in algal blooms, impoverished water clarity, de-oxygenation of water and death of fish and other aquatic life.

From the foregoing there is a clear need to minimise losses of N from agricultural sources to reduce the pollution of vulnerable habitats, emission of greenhouse gases and the incidence of plant, animal and human disease. In the light of this, any practise that can increase the N utilisation efficiency (NUE) and P utilisation at the soil, plant or animal level is of both environmental and financial benefit.

The need for biodiversity in UK grassland

Before the second world wars, extensively managed grasslands, particularly hay meadows were characteristically species-rich. However such bio-diversity declined when such grasslands were ploughed up and re-seeded with newly developed, highly competitive grass varieties that responded well to high applications of synthetic fertiliser, pesticides and herbicides. Many of the old meadow species could neither compete with the vigorous new grasses, nor tolerate high levels of fertiliser application. Indeed, it was reported in 1984 that 95% of grassland lacked significant wildlife diversity and only 3% had not been adversely affected by intensification (in Wilkins, 2000).

Grazing livestock stock are a crucial element of our landscape, 80% of which is shaped by farming (National Trust 2001), and 25% is semi natural habitat maintained by grazing animals (Countryside Survey 2000). Grazing is also essential for our livestock industry providing some 70 to 75% of the nutrients for UK ruminants (Mannetje 2000). Public opinion and organisations that promote naturalness and sustainability regard grazing cattle and sheep themselves as part of the landscape (Mannetje 2000), and grazing is also needed for bio-diversity and maintenance of particular habitats (Kirkham et al. 2005, Critchley 2004, Bishop and Wright 2003, Hetherington et al. 2002).

Sheep and cattle are essential for recovering and maintaining favourable condition of a wide range of grazed habitats. For example, around half of the UK’s Biodiversity Action Plan Habitats are considered dependant upon grazing by livestock for their conservation (Bullock & Armstrong 2000). However, the appropriate species, timing, density and related management practices are crucial (English Nature 2001). In practice, these are seldom in place by default (i.e. unless there is an explicit objective to conserve the habitat). The wrong grazing management can be as damaging as no grazing management. English Nature state that undergrazing is now as much if not more of a problem than overgrazing with 530 SSSIs undergrazed and 190 SSSIs overgrazed (English Nature 2005 (a)). Long term it would appear that more land might be undergrazed as stock numbers decline and the incentive to keep stock for subsidy has been removed (Silcock et al 2005).

As discussed below, changes in CAP are expected to lead to a reduction in grazing pressure of approximately 0.21 GLU/ha (from 1.67 to 1.46 GLU/ha) with the greatest reductions on larger

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farms (ADAS 2005c). It also seems that the balance of grazing pressure is likely to move away from cattle as farmers decrease cattle numbers faster than sheep numbers. On all farms, the proportion of grazing livestock units that are cattle is intended to go down from 79% to 72 % by 2010. Reductions in livestock numbers in the hills and uplands may have an adverse effect on the vegetation and associated wildlife (Silcock et al 2005). Some mitigation of these concerns will be dependent on the final policy outcomes for the hills and uplands and the degree of flexibility allowed for stocking rates in relation to habitat type and condition (Peel and Jefferson, 2000, Silcock et al., 2005).

Intensification of lowland livestock farming over the past 50 years has reduced the suitability of grassland as a feeding and breeding habitat for birds. The most important direct effects have been deterioration of the sward as nesting and wintering habitat, and loss of seed resources as food. Also, the abundance and diversity of invertebrates declines with reductions in sward diversity and structural complexity (Atkinson et al 2004).

Studies by Tallowin et al. (2005) and Buckingham & Peach (2005) provide an insight into how modified grazing management can improve biodiversity and habitat quality for farmland birds. Low input livestock systems are likely to be central to any future management strategies designed to maintain and restore the ecological diversity of semi-natural lowland grasslands. Old, unimproved grasslands, maintained by traditional management practices, including livestock grazing, are an important habitat. Meadows that are laid up for hay from early spring to mid summer are good for ground nesting birds such as redshank and snipe that require cover. Meadow nesting birds have suffered with the change from hay to silage due to earlier cutting dates and faster machinery (Andrews and Rebane1994). Silage fields are poor nesting habitats due to their dense fast growth, and early and frequent cutting.

Hay fields contain a variety of grasses and broad-leaved plants, many of which will have set seed before cutting, providing far more food for seed-eaters than silage fields managed as ryegrass monocultures cut before seed is set. Less seed food is available through the winter too, when the resulting fodder is fed to livestock. The large quantities of seed in dung, from stock fed on seed-rich herbage, are another important food source that is lost to birds (Atkinson et al. 2004). Hay may provide certain economic advantages to some beef and sheep farmers as in recent years the costs of making big bale silage in particular have increased. Hay does not pose any pollution risk (associated with silage effluent), does not create waste plastic (other than from baler twine) and tends to pose less animal health risks (listeriosis abortion can be an issue in sheep fed poor silage) than silage.

As discussed elsewhere in this report, forages (grazed and conserved) provide a significant proportion of the N and P requirements of ruminant livestock. Much of the protein in forages is rapidly degraded to ammonia-N in the rumen, but in the absence of an adequate supply of readily fermentable energy – which many forages lack – a large proportion of this N is excreted in the rumen, rather than being converted to microbial protein and available as a source of protein to the animal. Therefore reducing grazing pressure, and having more reliance on grazed or conserved herbage – rather than on concentrate feeds – would be expected to result in a reduction in feed N utilisation by the animal.

On the other hand, the amount of rumen degradable N in forages is closely linked to the total N content. This in turn is generally correlated with fertiliser N application rates. As a result, reductions in fertiliser N application, associated with the changes in grazing management described above, might be expected to result in lower levels of N consumed and excreted in urine 1

per unit area of land. In assessing optimum strategies for meeting then requirements of ruminant livestock, it is necessary to identify the criteria by which efficiency is to be measured. Apart from the need to satisfy the public demand for an aesthetically pleasing, unpolluted rural landscape, restoring bio-diversity is crucial to combat the reduction in the potential gene pool for future exploitation, for medical or agricultural purposes. Searches for new germplasm for agricultural use have tended to focus the best material from other agricultural enterprises, both at home and abroad. As a result, the material collected has tended to represent a relatively narrow

1 Provided that sufficient fermentable energy is available to the rumen micro-organisms is available to capture the N that is degraded.

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gene pool. However, both agricultural and non-agricultural varieties of ryegrass and clover exist. Populations selected from a wider range of non-agricultural habitats, representing extremes of both biotic and abiotic stress, have been found to be highly variable but to contain both the best and the worst yielding varieties when compared to control varieties. Populations arising from collections from agricultural sources, however, performed similarly to the controls. The benefits of maintaining bio-diversity are clear, and such ‘wild’ varieties may be hybridised with equivalent, cultivated varieties to produce more stress tolerant, agricultural cultivars (Sackville-Hamilton et al., 1998).

Section 3: Livestock numbers and their requirements for N and P

Livestock numbers

In 2002, the base year for this study, there were approximately 200 million head of livestock (including poultry) in Great Britain (Table 1). Between them, they consume over 20 million tonnes of concentrate feed, and in excess of 17 million tonnes of forage dry matter (DM).

Table 1. Livestock numbers (‘000 head) on agricultural holdings in Great Britain, June 2002 (Source: Defra Statistics).

England Wales Scotland Total

Cattle and calves

Total herd 5,531 1,195 1,935 8,661Dairy cows 1,462 268 199 1,929Beef cows 665 196 489 1,350

Other cattle 3,404 731 1,247 5,382Sheep and lambs 15,397 10,050 8,063 33,510Pigs 4,630 53.4 526 5,200Poultry Broilers 117,318 5,828 15,446 138,592

Layers 23,100 930 2,648 26,678Total poultry 130,971 6,072 15,544 152,587

Livestock numbers are not static, but change in response to external factors, including market demands, competition from imports for livestock products and the level of financial support received. On 1 January 2005, the direct support schemes for farmers as part of the Common Agricultural Policy (CAP) support2 were stopped and replaced by a Single Farm Payment Scheme (SFPS), which will be delivered to farmers irrespective of what they produce (i.e. ‘decoupled’ from production). The response to CAP reform in the UK livestock sector will be mixed. Oglethorpe (2005) has suggested that the majority of farmers will need to adjust their farming systems in order to make their systems economically viable. As a result there will be extensification in the uplands, accompanied by some substitution of beef with sheep. Some lowland livestock systems will intensify and specialise in certain areas and there may be some abandonment of marginal land.

Following the announcement of changes in CAP, a regular survey of farmers in England and Wales asked intentions for changes in livestock numbers3. Analysis of the survey data indicated that numbers of dairy cows, dairy followers, finishing beef and breeding ewes would fall following CAP reform (Table 2). The main conclusions of the survey are given below:

Intended reductions in livestock numbers are 12% for suckler cows, 12% for finishing beef, 9% for dairy cows and 4% for breeding ewes.

2 These included the Suckler Cow Premium, Beef Special Premium and Sheep Annual Premium Schemes3 “Farmers’ Voice” survey, sponsored and undertaken by ADAS in April 2004, with data analysed for English Nature.

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Those who understand the de-coupled nature of the SPS plan to make the largest changes. As understanding spreads, the intended changes are likely to become greater than reported here.

Intended reductions in suckler cow numbers are greatest in the hills and uplands (-35%) compared with the lowlands (–10%). Regionally suckler cow numbers are set to decline in all regions by close to 12%, representing a national issue where undergrazing is a problem.

Stocking rates are intended to decline from an average of about 1.85 Grazing Livestock Units (GLU) per ha. to 1.70.

The balance of grazing pressure will change slightly away from cattle (76% of all GLU as cattle reducing to 74% after adjustment to CAP reform).

Table 2. Livestock populations in the UK for ruminant livestock: Actual for 2001-20064 and simple linear trends for 2007-2009.

Year Dairy cows Beef cows Total other cattle Ewes and shearlings

Thousand head2001 2,251 1,708 5,942 17,9212002 2,227 1,657 5,733 17,6302003 2,192 1,700 5,945 17,5992004 2,131 1,736 5,186 17,6302005 2,063 1,762 5,200 16,9352006 2,046 1,710 5,014 16,448

2011 FV5 1,841 1,471 5,014 15,7902015 BAU 1,782 1,408 4,758 16,925

Note: Figures in Italics are projections and remainder are actual.

Simple linear extrapolations have not been made for ruminants since the step change in returns, as a result of CAP reforms, mean earlier trends are unlikely to be applicable post CAP reform. However, using simple linear trends have been used to estimate likely numbers of pigs and poultry (Table 3).

Table 3. Livestock Populations in the UK for Non-ruminant Livestock: Actual for 2000 to 2005/6 and simple linear trends for 2006/7 to 2009 (M. Temple, personal communication).

Year Breeding sows and in-pig gilts

Total pigs Chickens and table fowl

Laying hens

Thousand head2000 610 6,482 105,689 28,6872001 598 5,845 112,531 29,8952002 558 5,588 105,137 28,7782003 516 5,047 116,774 29,2742004 515 5,159 119,912 29,6622005 470 4,862 111,487 29,5502006 474 4,498 116,405 29,6012007 459 4,669 116,676 29,5482008 433 4586 117,839 29,7402009 421 4,535 116,554 29,708

4 Sources: Tables 3.2 of Agriculture in the UK 20065 2011 FV: Based on % intended change in numbers from FV 2006 survey of England: ADAS (2006) Farmers’ Intentions in the Context of CAP Reform – Analysis of ADAS Farmers’ Voice 2006 Survey of England and Wales, Report to Defra by ADAS, Wolves UK, WV6 8TQ.

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2015 BAU6 502 5,029 114,074 31,224

Note: Figures in italics are projections, remainder are actual.

Over the next few years, therefore, there is likely to be a reduction in the numbers of ruminants and pigs, while poultry numbers are expected to increase slightly. These changes will have an impact on the amount of feed required, and the form in which the N and P are supplied.

Livestock requirements for nitrogen and phosphorus

A number of authorities have published the requirements for N and P for individual animals or birds. These estimates are not always based on the same assumptions regarding N and P digestion and metabolism, and as a result there are frequently small differences in estimates of requirements. This uncertainty is compounded by the fact that estimates are generally based on the measurements of animals under controlled conditions. Since these may not reflect commercial practice, farmers and nutritionists frequently apply ‘safety margins’ to allow for differences. However, there is no ‘standard’ safety margin, and as a result there may be large differences in allowances for N and P in practice.

Estimates of the N and P requirements of livestock are given in Table 4, based on 2002 livestock data. For ruminants, the UK Metabolisable protein (MP) system (AFRC, 1993) was used to estimate requirements for N, while the NRC (2001) was used to estimating total P requirements (NRC, 2001). For pigs and poultry, NRC models were used for estimating both N and P requirements (NRC 1998 and 1994, respectively). The methods used and assumptions made to estimate total requirements are given in Appendix 2.

Table 4. Nitrogen and phosphorus requirements of livestock in Great Britain (based on 2002 census data).

Dairy Beef Sheep Pigs Poultry TotalNitrogen (tonnes N/year)

AFRC 360,199 100,561 464,6361,331,319

NRC 99,381 306,543

Phosphorus (tonnes P/year)

NRC 68,020 19,001 44,879 18,263 23,873 174,036

Total N requirements for all livestock are estimated to be approximately 1.3 million tonnes per annum. For P, NRC estimates of requirements (NRC 1985; NRC 1994; NRC 1996; NRC 1998; NRC 2001) have been used, and these suggest a total P requirement of approximately 174 kt per annum for all farm livestock.

Although these estimates of requirements are based on recently published reviews, there is nevertheless some uncertainty surrounding the exact requirements for N. For pigs and poultry, requirements are now more usually expressed in terms of essential amino acids, although there is still uncertainty as to the absolute amounts of amounts of essential amino acids required to achieve a given level of protein retention (Baker, 1996). For ruminants, much is known about the digestibility of feedstuffs but few of the biological mechanisms involved in the absorption and utilisation of protein N as free and peptide-bound amino acids have been identified. Even less is known about the whole animal and cellular events that regulate these processes and, therefore, ultimately control the extent of N retention. Similarly for P, requirements for different processes have not been completely identified. These uncertainties are usually accommodated within the

6 BAU: Renwick, A and Hodge, I. (2006). Business as Usual Projections of Agricultural Activities for the Water Framework Directive: Phase 2, report by SAC and University of Cambridge to the Environment Agency

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safety margins discussed above. The figures above are based on estimates of requirements, and do not include any safety margin.

The supply of nitrogen and phosphorus from feeds

Nitrogen is mainly supplied in the form of amino acids. Nine of these are believed to be ‘essential’ or indispensable, i.e. they cannot be synthesised in the body and must be supplied in the diet. The remaining 14 ‘non-essential amino acids’ can be synthesised in the body.

For pigs and poultry, the protein value of a feed is determined not only by the overall protein content, but also the balance of essential amino acids relative to the requirements for the different metabolic processes, e.g. maintenance, lean tissue growth, milk protein synthesis. Requirements for the essential amino acids have been published by a number of authorities e.g. NRC (1994) for poultry, NRC (1998), Whittemore et al., (2003) and van Milgen et al. (2005) for pigs. In addition, a number of livestock breeding companies have established AA requirements for their own progeny.

For ruminants, the amino acid profile of a feed is less critical, since much of the dietary protein is degraded to ammonia in the rumen. The N from rumen degraded protein is used by the rumen micro-organisms to synthesise microbial protein. This is a source of high quality protein for the host animal, capable of supplying up to 100% of the ‘protein’ requirements of ruminant livestock (depending on the level of production). The rate at which dietary protein is degraded to N in the rumen varies between feed types and level of feeding, which in turn affects the amount of dietary N ‘captured’ by the rumen micro-organisms. Thus the extent of degradation in the rumen significantly affects the nutritive value of a feed, particularly for highly productive ruminant livestock.

As discussed in more detail in Section 9 (page 52), the P in plant feed material is predominantly present as phytate-P. In this form it is largely indigestible by pigs and poultry, and because of this non-ruminant rations are usually supplemented with inorganic mineral supplements containing digestible P. In contrast, phytate-P is well utilised by ruminants because of phytase enzymes produced by the rumen micro-organisms.

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Section 4: Feeds for livestock

A wide range of materials is used as feeds for livestock. Many factors are involved in the selection of feeds - availability and cost are the primary considerations, but as the level of production (e.g. milk yield, liveweight gain) increases so the concentrations of essential nutrients within feeds takes on greater importance for the feed formulator. Both the levels and form of the protein and P in feeds are important factors in determining the suitability of a feed for a particular livestock enterprise, but because ruminants and non-ruminants digest and metabolise these nutrients differently, they have different nutritional values for different types of livestock. These factors also have a major impact on the amount and form of N and P excreted in faeces. Feeds are generally categorised as either concentrates or forages, and these are described separately below.

Forages

Most of the forage fed to ruminant livestock in Britain is derived from grassland. In Great Britain (GB), total land area is ~23 million ha, of which half is defined as agricultural grassland. Of this, 40% is improved grassland, 30 % semi-natural and 30% mountain, heath or bog (DEFRA 2002; LCM 2000; SEERAD, 2003). The areas and estimated yields of dry matter, N and P from these different land types are given in Appendix 5, and are also summarised in Table 5 (below).

In 2002, approximately one-third of the grass DM from improved grassland was conserved as hay or silage, the estimated amounts of, N and P in the conserved herbage being, 290,629 and 35,556 tonnes, respectively. As discussed below, other forages are also conserved as feeds for ruminants, but grass is the main conserved forage, accounting for ~ 80% of the total DM, N and P from all conserved forages in the UK.

The area sown to forage maize has increased steadily over the last 30-40 years, although has tended to plateau out at about 110-120 thousand hectares in recent years, and currently accounts for approximately 9% of the total conserved forage DM and P, and 6.5% of the N. Yields of N and P from forage maize in 2002 were estimated at 23,264 and 3,772 tonnes respectively.

Because of its low digestibility, cereal straw is not a major feed for livestock. Nevertheless it is estimated that ~355,000 tonnes of cereal straw DM was used as stock feed, providing approximately 2,500 and 375 tonnes of N and P, respectively.

Fodder beet, mangolds, kale, cabbage, forage rape, swedes and turnips, totalled approximately 119,600 tonnes in 2002, with estimated N and P yields of 2,870 and 478 tonnes respectively. Around 656,000 tonnes of beans and 6,807 tonnes of forage peas were used for stock feed in 2002, supplying an estimated 18,028 and 2,008 tonnes of N and P, respectively (SEERAD, 2003)

Approximately 30,200 tonnes of forages were imported in 2002; 53% were cereal husks and straw, 15% Lucerne meal or cubes and 30% swedes and mangolds (HM Customs and Excise – Commodities and Food). The total N and P contents of these imports were calculated to be 386 and 2.20t respectively.

From the figures above, the following estimates of forage DM, N and P available to ruminant livestock are given in Table 5.

Table 5. Estimated DM, N and P production (‘000 tonnes) from fresh and conserved forages in GB in 2002.

000' tonnes DM N PFresh herbage 54,440 1,3197 1488

Conserved forages9 15,209 344 44.2Total forage 69,649 1,663 192.427 N yields from different categories of grassland are given in Appendix 7.8 P yields from different categories of grassland are given in Appendix 8.9 See Appendix 9 for details of different categories of conserved forage.

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Although significant quantities of forage are available to ruminants, the utilisation of this forage DM by ruminants is very variable. Agricultural use of unimproved pastures is almost exclusively confined to grazing by sheep and beef cattle, with very little being conserved as hay or silage. Low stocking densities and inaccessibility of some unimproved land results in less than 50% of the available DM, N and P of unimproved pastures being utilised. As a result, estimated intakes of N and P from unimproved grassland were approximately 15% of the total intakes from fresh and conserved grass (Table 6), despite accounting for 60% of the British agricultural grassland area. The proportion of available DM, N and P grazed from improved pasture was estimated to be around 80%, the remaining 20% being ‘wasted’, due to factors including variable herbage palatability and herbage spoilage by excreta or treading. Losses of DM also occur during ensiling due to respiration in the field, (2-5%), fermentation in storage (2-10%), losses at feed-out (10%) and via outflow of effluent (Bastiman and Altman, 1985). Likewise, during haymaking, field losses may be 2-5% whilst mechanical handling of the crop may account for a further 15% loss. If the crop is rained upon, total DM losses may be as high as 30% (Watson and Nash, 1960). As a result, DM losses of herbage cut for conservation may be considerable. These factors have been taken into account in estimating the intake of forages by ruminant livestock.

Table 6. Estimated intakes (‘000 tonnes) of forage-derived DM, N and P by cattle and sheep in GB in 2002.

DM N PFresh grass Temporary grassland 5,406 163 16

Permanent pasture 13,926 428 36Unimproved pasture 7,511 150 18

Other forages 818 24 3Total fresh forage 27,661 765 73Forages – conserved Grass silage 8,667 222 22

Grass hay 2,308 40 7Maize silage 1,310 21 3Straw 320 2 0

Total conserved forage

12,605 285 32

Total all forage 40,266 1,050 105

Concentrate and compound feeds

Non-forage feeds are generally referred to as concentrates. Concentrates may be fed as individual ingredients, loose mixtures of ingredients (also known as ‘blends’), or as compound feeds. Where forages provide insufficient nutrients to meet production by ruminants, rations are supplemented with concentrate feeds. In contrast, monogastric livestock (pigs, poultry) are incapable of digesting forages to any significant extent, and as a result their diets consist almost entirely of concentrate and compound feeds.

A breakdown of the main sources of protein used in the manufacture of compound feeds is given in Appendix 3. In excess of 19 million tonnes of concentrate feeds are fed to livestock in Great Britain each year, providing approximately 290 kt of N and 125 kt P. As illustrated in Figure 2, more than half the N used in the manufacture of compound feeds is derived from oil seed meals. Of this, just over half of this is provided by imported soya bean meal. Cereals (predominantly wheat and barley) account for a further ~21% and cereal by-products (such as maize gluten feed and wheat feed) a further 12%.

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Regrettably, but perhaps understandably, the data on feed use is provided in such a way as to make it impossible to identify the quantities of individual feed types that are fed to the different classes of livestock. As a result, the consequences of changes in the availability or supply of a particular raw material on feed use and production by an individual livestock sector are difficult to estimate.

Ingredient composition: factors of influence

Most of the protein in compound feeds manufactured for high yielding lactating dairy cows is obtained from combinations of soya bean meal, rapeseed meal, maize gluten feed, pulses and cereals. Soya bean meal has a superior amino acid profile, lower rumen degradability and higher protein concentration than most other vegetable proteins10, and therefore would be the protein supplement of choice in most ruminant diets.

The main feature of note is the wide range of raw materials used for livestock feeds, each having their own distinctive nutritional characteristics. The composition of compound feed is determined by three main criteria:

Price of the available ingredient; Nutritional value; Specific requirements of the livestock to be fed.

The price is the most important factor determining which feed ingredients and what quantities are incorporated into a particular feed (within nutritive limits). Hence it is the price of one protein ingredient relative to another protein ingredient that is of key importance. This is not surprising, when about 80% of the cost of an animal feed is accounted for by the ingredients, and feed costs11 account for about 80%-90%, 75%-85% and 70%-80% respectively of total variable costs of production for poultry reared for meat, dairy farmers and pigs. As such, the use of least cost feed formulations12 is a widespread practice in UK feed manufacture. The nutritional composition of feed will vary as any given ration mix serves specific livestock types. Thus it varies by animal type, age of animal and the purpose it is being raised (e.g., eggs, meat, milk).

In terms of preferences for different protein sources, soya bean meal is the most used source and is generally considered as the standard against which alternatives are measured against. General preference for soya reflects

Its high level of protein relative to all other sources (with the exceptions of fish meal and meat and bone meal, MBM);

Abundant and consistent availability; Consistent price competitiveness relative to alternatives – this does, however vary with time; A higher level of lysine (but slightly lower levels of methionine and cystine) than other

vegetable-based products like rapeseed meal. Overall these are the amino acids most deficient in cereals, and hence the desirability for incorporating oilseeds with cereals.

The higher level of lysine in soyabean meal compared to other vegetable proteins means that it is particularly attractive as an ingredient for feeds used in the pig and poultry sectors13. In the ruminant sector, this is less vital and hence other feeds like rapeseed meal tends to be more readily substituted for soya in the ruminant feed sector.

Least-cost ration formulation programmes are extremely sensitive to the nutritional constraints of the ration, the composition of the feeds and their costs. As a result the number of ingredients and their inclusion rate can alter significantly with small changes in the costs of individual nutrients and/or diet specification. A change of just a few pounds per tonne can often make the difference

10 Of the most commonly used feeds, only maize gluten meal has a higher protein content, but it has a lower lysine concentration.11 Including forage costs.12 Using mathematical programming techniques such as linear programming13 Rapeseed meal is also considered by some to adversely affect meat quality (flavour) when used in poultry finisher rations.

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between incorporating an ingredient at its maximum inclusion rate and excluding it completely. This is particularly significant within the context of this study. In the absence of any external pressure to do otherwise, the use of alternative feeds that could potentially improve utilisation of dietary N or P will be determined largely by the cost of the feed, and not any environmental impact that their use may have.

A significant proportion of the concentrates used as livestock feeds are imported. Absolute amounts vary from year to year, depending on price, availability and demand; average values for five years (1998-2002) are given in Appendix 4. This table illustrates the wide range of feeds imported into the UK. Based on typical values for the N and P content of these feeds, it is estimated that imported feeds account for 43% and 28% of the total N and P, respectively, provided by concentrate feeds, and 14% and 15% of total N and P, respectively, supplied by all feeds. It should be noted that this list does not include mineral supplements, which supply considerable amounts of P.

Summary of N and P demand and supply

Using estimates of forages and compound feeds consumed by livestock in Great Britain, and making certain assumptions regarding their N and P contents, a comparison has been made between the supply of DM, N and P (Table 6) and estimates of requirements (Table 4).

Table 7. A comparison of the requirements for N and P with supply from different feed categories (‘000 tonnes).

Supply Requirements “Surplus”'000 tonnes Proportion

NitrogenCompound feeds 296 0.19Concentrates 212 0.13Grain fed on farm 58 0.04Fresh forages 765 0.47Conserved forages 285 0.18Total 1,616 1,331 285

PhosphorusCompound feeds 83 0.35Concentrates 42 0.17Grain fed on farm 11 0.05Fresh forages 73 0.30Conserved forages 32 0.13Total 241 174 67

The supply of N and P are compared with requirements above. Approximately 1,656 kt of N and 238 kt tonnes of P are fed annually, which are 24% and 36% in excess of requirements.

With the exception of forages, which are consumed almost exclusively by ruminants, it has is not possible to assess the proportion of a given feed material that is fed to the different forms of livestock. However, from published data (for concentrate feeds) and estimates of intakes (of forages), the contribution of each feed type to N and P supply has been calculated. Forages make the largest contribution to N and P supply (65% and 44%, respectively).

How ‘robust’ are these comparisons of supply and requirements? Because no national audit of farm feeding practices is undertaken in the UK, the only source of data on feed use is that provided by Defra Economics and Statistics Division. These data only cover the main traded commodities and compound feeds from the major manufacturers. They do not include many co-products sold directly onto farms (e.g. confectionery co-products). Nor do they include the amount of mineral feedingstuffs used either in the manufacture of compound feeds or directly on farms.

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Uncertainty also surrounds the estimates of cereals fed on farm and inter-farm trading. Problems of estimating the amount of forage consumed by grazing livestock have already been alluded to (page 13). Put together, the amounts of N and P supplied by feeds (Table 7) are likely to significantly underestimate what happens in practice, and the true “surpluses” will be greater than indicated above.

In order to retain consistency, 2002 has been used as the base year for comparing livestock requirements with supply, although both sets of data have changed in the intervening period. Changes in livestock numbers are discussed elsewhere (page 9). On the feed supply side, there has been a marked reduction in the quantity of compound feed manufactured; in the last 12 months alone this has declined by about 6.5%. N supply from concentrate feeds has declined from 566 kt in 2002 to 525 kt in 2005. For P, concentrate supply has declined from 136 to 122 kt in the same period. These changes are most likely to reflect the reduction in livestock numbers, but may also reflect improvement in N and P utilisation efficiency; in particular there is some evidence that production of livestock products (milk and meat) from forage has increased slightly over this period.

Despite uncertainties over the precise amounts, excesses on this scale are clearly undesirable, both environmentally and economically. One option for reducing N and P excretion would simply be a blanket reduction in N and P inputs. However, in most situations this would result in lower levels of output for producers, with major economic implications. This report describes strategies for improving the utilisation of these nutrients without adversely affecting the health, production or reproduction of the livestock concerned. But because their digestion and metabolism are so different, they are dealt with in separate parts of the report. Strategies for improving P utilisation are described on page 51.

Feeds used by livestock are typically classified as being either ‘forages’ or ‘concentrates’. The following sections describe characteristics of both these groups of feeds that influence their N utilisation, before discussing (on page 32) feed and management strategies for improving N utilisation. Options for improving P utilisation are described on page 54.

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Section 5: Forages – Optimising N utilisation

Ruminants receive most of their N from grass-based forages. Yet ruminants are particularly inefficient at converting this N into milk and meat protein. On dairy farms, between 20 and 35% of the N consumed by the herd is retained in the protein of the milk and meat produced, with the remainder excreted in manure (Van Vuuren and Meijs, 1987; Charmley et al., 1988; Tamminga, 1992; Dou et al., 1996). Pasture-produced beef has been reported to have an N use efficiency of less than 10% (Hutchings et al., 1996) and sheep typically incorporate 5-10% or 3-15% respectively of ingested N into meat or meat and wool (Henzell and Ross, 1973). The un-retained N is excreted and lost to the environment. Such low nitrogen use efficiency (NUE) is costly both in financial and environmental terms.

This poor utilisation is generally attributed to an imbalance in the supply of fermentable energy and degraded N to rumen micro-organisms. As a result, strategies aimed at improving NUE have tended to focus on ways of reducing this imbalance. Two general approaches have been identified to improve N utilisation. The first is by changing the forage crops, either through plant breeding or processing. A number of technological advances have been made which will allow whole farm NUE of forage crops to be enhanced, without the need for significant changes in current practise, and these are described below. The second approach is by diet manipulation (page), and in particular the choice of forage crop or supplementary feed.

(i) Plant breeding and conservation

Grass

As discussed in more detail on page 20, the utilisation of forage N is significantly influenced by the supply of readily available carbohydrate in the rumen. Therefore, plant breeding programmes have been undertaken to develop ryegrass varieties that express consistently higher water soluble carbohydrate (WSC) levels than conventional varieties. The potential for such ‘high sugar grasses’ (HSG) to improve NUE is high. New perennial ryegrass (PRG) varieties have been produced which accumulate on average 280g WSC/kg DM (range 150-370) which, when evaluated throughout two growing seasons, consistently yielded 3.6% units more WSC than the previous HSG, Aberdart (Table 8). Dry matter and WSC yields were some 15% and 35% greater, respectively, than seen for Aberdart. Similar improvements in WSC content and yield have been noted for newer Hybrid ryegrass varieties. Additional breeding lines are being developed from the same breeding line that produced Ba 13582 which show further potential for increasing the WSC content and DM yield of ryegrass varieties (Wilkins and Lovatt, 2004).

Table 8. Average WSC content, relative DM yield, and WSC yield during 2003 and 2004 of varieties of perennial (PRG) and Hybrid ryegrass developed since 1990.

Variety Year of synthesis

Average WSC content (g/kg DM)

Average Relative DM yield

Average RelativeWSC yield

PRGBa 13582 2000 278 115 135AberDart 1991 238 100 100Hybrid RGAberecho 1994 279 113 135AberExcel 1988 222 100 100

Conventional breeding of new plant varieties can take around 15 years, due to time consuming screening of large numbers of traits. However, marker assisted selection techniques can drastically reduce this time period as significantly improve the precision with which new characteristic combinations can be assembled. Thus molecular fingerprinting techniques are being used to rapidly develop ryegrass varieties with enhanced NUE by grazing livestock. These new varieties maintain yields, but allow a 30% reduction in the amount of fertiliser applied to swards for dairy cattle (Humphreys, 2000). White clover varieties that are better utilised by livestock are also being developed by molecular means (Abberton et al., 2004). The effects on NUE as a result of feeding these high-sugar grasses are described on page 44.

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Forage Maize

To realise the potential of forage maize, it is important that varieties are chosen that are able to complete their development within a given locality. Recent advances in breeding forage maize have produced varieties that are capable of germinating and growing at lower temperatures than previous cultivars. This has resulted in growth and production of acceptable yields in increasingly northern and marginal localities, such that it is predicted that forage maize could be grown in virtually all-lowland areas of England. In areas favourable for growing maize these extremely early varieties may allow double cropping or optimum entry to autumn crops (Maizeology, 2001).

Red Clover

Ensiling is an important method for preserving forages for animal production systems in the UK. A major problem in silage production is the extensive protein degradation that occurs during the ensiling process, resulting in economic losses and negative environmental impacts due to increased animal excretion of nitrogen. Red clover silage retains over 80% of its protein as true protein resulting in improved animal performance. Reduced proteolysis in red cover is correlated with the presence of a soluble polyphenol oxidase (PPO). Breeding programmes aimed at developing Red Clover varieties with enhanced PPO contents have been established. New research has also found the presence of PPO in some pasture grasses including perennial and Italian rye grasses, although none has been found in fescues. It is of note that in preliminary studies protein losses in fescue silages were some 15 % higher than from perennial ryegrass silages. These data may suggest that PPO in grasses could protect grass protein in a similar manner to that of red clover. If this is confirmed, then there is the possibility of breeding grasses with enhanced PPO content and increased protein protection (Kingston–Smith et al., 2004).

Forage conservation

Over 25% of forage N consumed by ruminants derives from conserved forages. When conserving forage crops, there are measures that livestock farmers can take that can help improve forage N utilisation. Mower conditioners fitted with rubber rollers are now available, which permit rapid wilting of the stem without causing undue leaf damage – a particular problem when harvesting legumes - and minimising field losses. Rapid wilting is desirable to reduce losses resulting from plant-mediated proteolysis and metabolism of WSC prior to ensilage. Conditioning with rubber rollers limits proteolysis during wilting by shortening field-wilting time and possibly accelerates release of tannins (Cavallarin et al., 2002b). When wilted to >40% DM, conditioning further improved protein preservation by decreasing proteolysis and amino acid catabolism (Cavallarin et al., 2002b). From an environmental perspective, compared to direct cut silages, the higher DM of those crops that have been wilted reduces the volume of silage effluent, and thus the potential for pollution.

Breakdown of plant protein (proteolysis) commences immediately the crop is harvested, and continues during the ensiling process. As a result, grass silage frequently has low true-protein (TP) and high non-protein nitrogen (NPN) contents. Generally, the higher the TP:NPN ratio, the greater the NUE of the forage. In well preserved, inoculant-treated grass silage the TP:NPN ratio may be 65:35, compared with 20:80 in those that are less well preserved (Winters et al., 2000). Additionally, grass silage is often low in NSC, these being utilised during ensilage (Davies, 1998), further aggravating the poor NSC:N ratio of the original sward. However, a 5.0 % unit differential in WSC content between HSG and control grass silage was sufficient to elicit ca. 30% increase in NUE in steers in vivo (Merry et al., 2005).

During ensilage, a rapid fall in pH is desirable to reduce proteolysis and maintain WSC levels. In the absence of additives or inoculants, reductions in pH can be slow, resulting in grass silage with low residual WSC and high NPN contents. However, a wide range of silage additives is now available that help improve forage conservation and hence N utilisation. Additives may be acids, sugars (e.g. molasses), enzymes (usually fibrolytic) and bacterial cultures, all of which are used to promote a rapid fall in pH during ensilage with consequent preservation of protein, WSC and hygienic status. Several types of bacterial culture are available, most commonly freeze dried cultures of Lactobacillus plantarum. However, although reasonably successful in enhancing silage quality, they appear to be less effective at preserving silage than when freshly cultured

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preparations are used. Freshly cultured inoculants avoid the initial lag experienced with those that are freeze dried, and as a consequence result in silages with enhanced fermentation characteristics and consistently reduced proteolysis and improved preservation of true protein (Cussen et al., 1995; Davies et al., 1998). The major constituents of the WSC fraction of temperate grasses are fructans14, the remaining constituents being the simple sugars, glucose, fructose and sucrose. Very few strains of L. plantarum can utilise fructans - only 2 out of 246 strains surveyed had fructan-degrading activity (Winters et al., 1998). Thus the majority of inoculants can only use a portion of the plant WSC for silage preservation. However, new inoculants containing fructan-degrading strains of L. plantarum (Strain Aber F1) have been developed, and which have improved protein protection over a standard commercially available inoculant and the untreated control by 22 and 30% respectively. Additionally, beef cattle fed silage inoculated with Aber F1 had 30 and 45% higher daily liveweight gain than the commercial inoculant or the untreated control respectively. Clearly, development of such inoculants should aid in addressing some of the inefficiencies associated with the use of grass silage (Davies et al., 2000 a). Use of evolutionary computer models using genetic algorithms has helped identify ‘designer’ silage additives (Davies et al., 2000 b; Johnson et al., 2004). However, as a result of recent changes in EU legislation,15 all silage additives will need to undergo an approval process by October 2011. This will apply both to products currently in use and any new products prior to being marketed16. The approval process, which will include a requirement to demonstrate safety and efficacy, will have significant cost implications for silage additive manufacturers. As a result it is likely to markedly reduce the number of new additives coming on to the market, as well as removing from sale some of those currently and successfully being used.

Animal performance can sometimes be enhanced when inoculated silages are fed. Compared to well preserved un-inoculated control grass silage, inoculated grass silage was reported to improve NUE in lambs (Fraser in Moorby and McConochie, 2003) and increase VDMI and LWG of steers (Davies et al., 2000a).

Forage maize has naturally low levels of N and high WSC contents, and generally a good fermentation can be achieved without the use of an additive. There are reports that dry matter intakes and production may be improved with the use of certain inoculant additives at ensiling, but no evidence that NUE is improved.

(ii) Forage selection, management and supplementation

In ruminant livestock, the rumen microflora provide the animal with a substantial portion of its protein requirements. For efficient microbial protein synthesis (MPS) both a readily degradable source of protein and fermentable energy (in particular rapidly available sugars and/or starch and other non-structural carbohydrates (NSC)) are required. Although up to 85% of forage protein is rapidly degraded in the rumen (Van Vuuren et al., 1990) forages are often low in fermentable energy, resulting in a low ‘capture’ of the rumen degraded protein by the rumen micro-organisms. This results in ammonia accumulation in the rumen, much of which is excreted via urine, and reduced nitrogen utilisation efficiency (NUE). Supplementation of forages with NSC results in greater efficiency of MPS, lower rumen ammonia concentrations and increased MPS (Chamberlain et al; 1993). Thus, NUE increased from 18 to 27% when dairy cows were given NSC-rich forage (Valk, 1994). The effects of an imbalance between rumen-degraded N and fermentable energy become more pronounced as dietary N levels increase. It has been suggested that at dietary N levels greater than 27.4g N/kg DM, rumen N losses become particularly enhanced (Ullyatt et al., 1988; Van Vuuren et al., 1990), yet early season swards often have much higher N contents than this (Waite, 1965).

Strategies to improve NUE of forages include have therefore focussed on ways of improving the supply of fermentable energy relative to degraded N in the rumen and/or reducing the amount of rumen degradable protein that is excess to requirements of the rumen micro-organisms, and these are described below.

14 Polymers based on fructose15 Regulation (EC) No. 1831/2003 of the European Parliament and of the Council.16 All current silage additives will need to have been approved for use as such by 2011.

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Grass

Although supplementation of grass with NSC increases NUE, it may be difficult to achieve appropriate supplement intakes, both temporally and quantitatively, by the entire grazing herd. Use of grasses that accumulate elevated levels of water-soluble carbohydrate (WSC), the so-called ‘high sugar grasses’ (see page 18) can help improve the NSC: N ratio and result in improved NUE without recourse to supplements.

Water-soluble carbohydrates accumulate when the supply of photosynthesis exceeds demands for plant growth and metabolism. Levels range from 20>350 g WSC/kg DM (Wilkins and Lovatt, 2004), with high levels typically present in late spring and autumn, and lower levels mid-season. This pattern is inversely related to sward N content, and application of N fertiliser to swards results in higher N and lower WSC contents. The inefficiencies of N capture from early spring grass, and the effects of seasonal variations in WSC:N ratios of grasses on NUE, have been clearly demonstrated (Ulyatt et al., 1988). Where grass is supplemented with concentrates, appropriate feed selection may help improve NUE.

The generally weak NSC:N ratio in grass suggests that in terms of NUE, it is a poor feed for ruminants. However, strategic grazing management can improve NUE. Dairy cattle turned out in the afternoon when WSC contents were highest yielded more milk, despite having similar feed intakes to those pastured in the morning (Orr et al., 1998). Sheep (Lee et al., 2001a), dairy cows (Miller et al., 2001) and beef cattle (Lee et al; 2001b; 2002) fed high sugar grass (HSG) have all showed positive production and/or NUE responses compared to those fed control swards of lower WSC content. The forage intake of ewes and their lambs, grazing on HSG perennial ryegrass or a control variety were similar, but lamb LWG, production (LWG/ha) ewe carrying capacity and lamb NUE were respectively 12, 23, and 15 and 11% greater on the HSG than the control (Lee et al., 2001). Taken across the trial there was a strong positive correlation between pasture WSC and lamb LWG. In dairy cows, digestibility of HSG was greater than the control grass with HSG eliciting an average increase in milk yield of some 2.5kg/d, and a 24% reduction in urinary N coupled with gains in body protein during early lactation: the control cows lost body protein (Moorby, 2001).

Forage maize and maize silage

Forage maize is now firmly established as a major forage feed for ruminants in the UK, and as described later (page 34) the substitution of grass silage with maize silage can have a marked improvement in NUE by ruminants. The area sown to maize in the UK has increased dramatically over the last 30 years, from about 30,000 ha in the 1970’s to 130,000 ha in 2001, but has been stable for some years. The rapid expansion during the 1990’s was due to a combination of factors, including the introduction of new varieties which were better adapted to UK conditions, warmer weather and the introduction in 1993 of an arable payment scheme under the Common Agricultural Policy. The DM yield of forge maize is greater than that of ryegrass, averaging 12t/ha. Growth of standard varieties of FM is currently confined to warmer lowland parts of England and Wales, due to the vulnerability of the crop to poor weather during establishment. An average crop of forage maize will use 160kg N/ha, while oversupply of N will result in too much leaf, insufficient grain, delayed maturity and lodged crops. As it is very efficient at extracting soil N, no more than 100kg N/ha from fertiliser is normally required. Most of the forage maize in Britain is fed to cattle as whole crop maize silage (Wadswoth, 2003). This has an enhanced NSC:N ratio compared with grass silage due to its low N (1.6gN/kg DM) and high starch content (200-300g/kg DM). Further benefits of maize silage over grass silage include a reduction in both the area required for conservation - due to its high DM yield – and lower requirements for inorganic fertiliser, because its high uptake of N makes it an ideal crop to utilise organic manures. Additionally, it is harvested in one operation (Wadsworth, 2003).

In future, the area under production might be expected to increase if predicted increases in temperatures are realised. The advent of new extremely early varieties, however, that are less susceptible to adverse conditions, will allow expansion of the acreage of FM in the UK, such that most of lowland England should be able to grow the crop successfully (Maizeology, 2001). However, elevated temperatures will favour higher maize yields only where there is sufficient soil moisture. Simulation studies have predicted that higher temperatures accompanied by a reduction in precipitation would result in a reduction in DM yields in the south and south-east of

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England (Cooper and McGechan, 1996; Davies et al, 1996). Since the value of the crop is insufficient to justify irrigation, expansion in the production of maize may be concentrated in the western and northern regions of the UK, which receive higher rainfall but are currently too cool for maize production.

In addition to a larger geographical area suitable for the growth of forage maize, there is no evidence that the yield potential of forage maize cultivars may not have reached its limit (Cottrill, Gooding and Givens, 2005). However, the extent to which this can continue is unclear. As a result of the move to the Single Farm Payment Scheme, the place of maize is in some doubt from a crop margin perspective. This may be particularly so on rented land, which may be affected by the SPS rules because entitlements will generally be owned by the landowner, making the maize less economic to grow, even at very low rents.

Forage legumes

Legumes are generally regarded as being agriculturally beneficial due to their ability to ‘fix’ atmospheric nitrogen, rendering both the plant and the rhizosphere high in N. Indeed, white clover (WC) grass mixes have been shown to support similar levels of ruminant production (Davies and Hopkins, 1996) to that of grass fertilised with 200kg N/ha. The use of legumes therefore provides an opportunity of reducing use of synthetic fertiliser.

The perception that biologically fixed N has less environmental impact than that derived from synthetic fertilisers is unsound, as N losses are related to the total N input rather than its origin. The N pollution emanating from legume forages can be significant. Nitrogen leached from soil beneath stands of red clover (RC) or WC was slightly greater than that from grassland fertilised with 200kg N/ha (Scholefield et al., 2001). When unfertilised grass/clover swards were compared with N-fertilised grass there were little differences in the quantities of leached nitrate (Cuttle et al., 1992). Therefore, the combination of high levels of N leaching from forage legumes and their low NUE by livestock suggests that they may not be suitable as the major portion of the forage ration for ruminant systems designed to maximise NUE and minimise the environmental burden. Their judicious admixture with high WSC/low N forages may be more appropriate in this regard. However, greater NUE can be obtained from legumes containing substances that reduce N degradation in the rumen.

Forage legumes such as birdsfoot trefoil (Lotus corniculatus) and sainfoin (Onobrychis vicifolia) contain condensed tannins that bind to proteins, protecting them from rumen proteolysis. The tannin/protein complex dissociates post-ruminally, rendering the protein available for use by the animal. Thus, tannins in fresh L. corniculatus have been shown to reduce rumen ammonia by 40-50%, increase NAN flow to the small intestine by 40% (Waghorn et al., 1987), increase VFI and milk yield in dairy cows, (Woodward and Reed, 1989), and increase LWG, carcass gains and wool growth in sheep (Wang et al., 1996). Such beneficial affects of condensed tannins are only observed at low levels (10-55g tannin/kg DM) of dietary inclusion; higher levels can reduce both VFI and diet digestibility (Barry and Duncan, 1984; Barry et al., 1986). Low levels of dietary tannins can also prevent bloat, a condition that can afflict ruminants grazing forage legumes such as clover or Lucerne (Mangan, 1988). Lotus and sainfoin are regarded as non-bloating species. However, yield and persistency of lotus (Davies and Fothergill, 2000; Halling et al., 2001) and sainfoin may be poor, particularly in mixed swards.

Although RC does not contain condensed tannins, it contains a protein protectant, polyphenol oxidase (PPO), such that proteolysis of RC protein during ensilage was 7-40% compared with 45- 90% of that of ensiled Lucerne (Jones et al., 1995; Cavallarin, et al; 2002a). The efficiency of MPS in vitro was enhanced when RC silage (RCS) was mixed with grass silage (70:30) by 22% (Merry, et al., 2002). The NUE of RCS for milk has been shown to be higher than from Lucerne silage (Broderick, 2002) and from four forage legumes (Bertilsson et al., 2001), but lower than that of grass silage. Mixing RCS with grass silage raised the NUE for milk by 11-15% compared to when RCS was the sole forage (Bertilsson et al., 2001), whilst maintaining the higher DMI and milk yields observed when RCS rather than grass silage was fed as the sole forage. Likewise, when compared with grass silage, mixtures of RCS and maize silage (25:75) resulted in increased DMI, improved milk yield (7.5 kg/d) with the NUE for milk being raised by 14%. This represented a 35 g N /d reduction in urinary N loss per animal, (Dewhurst et al., 2005) which, for the entire

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2002 British dairy herd, is equivalent to a reduction of 18 677 t urinary N per annum. RC also contains formonetin, a phytoestrogen which has been associated with increased lamb LWG, (Fraser, 2004; Moorby et al., 2004) but may reduce ewe fertility.

A number of other forage crops have also been considered as sources of ‘bypass’ protein. The British acreage of white lupins has increased to ca. 20,000 ha, as it is perceived that they are a valuable home-grown protein source. While most lupins currently being grown will be harvested for their seed, there has been some interest in growing lupins as a forage crop for ensiling, and subsequent use as a feed for ruminants. Some varieties of lupins are susceptible to a fungal disease, Phomopsis stem blight, in which the fungus produces a mycotoxin. Phomopsis was found on at least one crop in the UK last year, although there is no evidence that farm livestock have been affected. There have been a number of reports - particularly from Australia - of ruminant animals dying after consuming forage lupin or lupin stubble that had been infected with this fungus. However, phomopsis-resistant strains of lupins have been developed and livestock may safely graze the stubble from these crops.

Early studies on forage lupins carried out in New Zealand (e.g. Burt and Hill, 1981; Janson, 1984) demonstrated the potential for grazing and inter-cropping. Sheldrick et al (1980) and Sheldrick et al (1995) reviewed the forage potential of Lupinus albus (White lupin) and L. angustifolius (Narrow leaved lupin) and concluded that they were capable of good yields of moderate quality forage under UK conditions. L. albus showed the most promise with yields of about 11 tonne DM ha -1

with a feed quality similar to that of forage peas, but with a substantially increased yield potential. Samic and Ramosevac (1983) referred to the ability of L. albus to produce large amounts of forage in a short period, which made it suitable for forage production in regions with a short growing season. Wilkins and Jones (2000) reviewed recent progress in plant breeding, opening up the possibility for increased use of lupins for forage. Lupin protein has lower rates of degradation in the rumen than peas or beans and could form an effective complement to grass (or maize) silage.

The feed quality of forage lupins is similar to that of peas (15% protein) but DM yields are higher – around 11 t/ha (Sheldrick, et al., 1980, 1985). Furthermore, protein from lupins is less rapidly degraded in the rumen than that from peas, and could form an effective accompaniment to grass silage or maize silage. There is also reduced soil accumulation of N associated with lupins compared with peas (Haynes et al., 1993) and lupins ‘scavenge’ soil P, thus potentially reducing the polluting effects of excess levels of these elements.

Compared to grass, forage peas contain higher levels of N and starch, and milk yields by dairy cows fed pea/ wheat silage and 4 kg of concentrates were equivalent to those fed grass silage plus 8 kg concentrates. However, NUE was lower for the mixed crop silage (Adesogan et al., 2000). Forage peas are a short-lived crop enabling succeeding crops to be grown in the same season, and thus kale may follow peas for autumn and winter feeding, using the excess N in the system. Kale contains significant levels of N and WSC and is highly digestible (Young et al., 1997), but when ensiled is low in residual WSC and trueprotein (Fraser et al., 1999). However, when ensiled as a bi-crop (kale: barley 20:80) and fed to dairy cows, Moorby et al., (2003) reported reduced urinary N outputs and greater milk N contents compared to when grass silage was fed.

Fertiliser used to achieve home-produced inputs

In addition to the N and P supplied from purchased feeds, considerable quantities are imported onto farms in the form of fertiliser. The areas, fertiliser inputs, yields, N contents, utilisation and thus the ‘N balances’ (inputs minus off-takes) and ‘net inputs’ (inputs minus exports) for farming are shown in Appendix 16. Most detail is shown for arable crops; forage crops are shown by way of comparison. Overall, the annual net N input to agriculture is very large (>2 Mt N) compared with N exports (135 kt N). Note that, whilst the estimation of N exports from agriculture in this table is crude, it is generally the case that only a small proportion of N-containing residues from arable crops are exported from agriculture; they are usually returned in feeds. Thus, fertilisers and Rhizobial fixation are much the most important component of N imported into agriculture. N in imported feeds is the other main component of N imports; these are described and quantified in Section 3 (above).

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Rhizobial N fixation is not easy to estimate with confidence, but is undoubtedly much less important than fertilisers in introducing N to UK agriculture as far as arable crops are concerned. Most non-harvested components of crops (straw, haulm, etc.) are either returned to the soil after harvest, or in farm-yard manures after use as animal bedding, so these have not been included in exported N. The N balances thus allow comparison of the immediate influences of individual crops on the N status of the land.

Of the arable crops, wheat is dominant, even if it is considered separately as two crops with different uses: bread making, and feed-seed-export etc. Due to its large acreage and high requirement for fertiliser N, ‘feed’ wheat is responsible for more than a quarter of arable N inputs and a third of net N imports. Although ‘bread’ wheat uses 75% of the fertiliser N that is used on ‘feed’ wheat, it has less than half the effect on net N imports because it is exported as food. The other major crops contributing to net N imports are oilseed rape, feed barley, and field beans. Malting barley and field peas also contribute, but the remaining crops together only contribute 5% of net N imports.

The significance of net N imports is that they must either be lost to the environment through leaching of nitrate, or emission of nitrogen gases such as nitrous oxide (N 2O) or NH4, or they must raise the N status of arable land. The N accumulated by land is almost entirely in organic form. This organic-N can be broken down and release significant amounts of mineral-N, which can be used by crops. However, the mineralisation of OM is often poorly synchronised with crop requirement, especially autumn mineralisation, and much of it is lost as polluting forms of N, mainly NO3.

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Section 6: Concentrate feed selection and management

As illustrated in Table 7, non-forage crops make a significant contribution to N supply to farm animals, either directly or as co-products of manufacturing of food for human consumption: examples of the latter include brewers’ grains, sugar beet pulp, and stock feed potatoes. The major non-forage contributors, however, are the cereals and oilseed meals. Just over 50% of the N used in the manufacture of compound feeds is derived from oilseed meals (Figure 2, page 14). Of this, soya beans (which are not grown in the UK) provide half. In general, cereals are treated primarily as sources of energy, but they also make a significant contribution to the overall N intake of farm animals, particularly pigs and poultry. Approximately 38% of the N in manufactured compound feeds is derived from home-grown cereals and cereal by-products. The remainder of the N is supplied by animal proteins (particularly fish meal), by-products of the food industry, peas and beans, and ‘other’ feeds not listed elsewhere.

Cereals

The small and large-grained cereals are generally low in protein and deficient in a number of the essential amino acids17. However, the potential for correcting these weaknesses is good in some of the cereal grains. Over 90 breeding cycles, strains of maize containing between 4.8 and 32.3% crude protein have been developed. As with most varieties, however, the quality of protein in high protein lines is low.

Wheat is the main cereal fed to livestock in the UK and the main constituent of non-ruminant diets; it will therefore be the main species for discussion here. Wheat is largely valued for it’s energy content and its low cost relative to other energy sources (for instance barley, which has a higher fibre content and so less metabolisable energy, and maize which has to be imported and so is more expensive per unit energy). However, it is also an important source of protein. In typical non-ruminant rations, the N provided by wheat may account for up to 40% of the total dietary N.

Although wheat usage in feeds is large (40% of UK wheat production is used as livestock feed), to date wheat has not been bred specifically for livestock feeding, and given any lack of price differentiation in the market there is little moderation of husbandry to affect feed quality. Less wheat is used for bread than for feed, but the bread market supports a premium for grain of bread making quality so, other than crop yield, wheat breeding has focussed primarily on improving quality for making bread. Bread making requires grain with a significant content of gluten protein, and since wheat breeding programmes are integrated, in the sense that all markets are addressed by the same programme, protein concentration has been regarded generally as a positive attribute of wheat. What is more, the HGCA testing regime, which sets the benchmarks for all wheat breeding programmes in the UK, has adopted super-optimal N fertiliser levels in its testing protocols (by 50 kg/ha N, enough to raise grain protein concentration by 0.5-1.0%). The intention is to fully express all varieties’ potential for protein concentration. Together, the integration of feed and bread-wheat breeding, and the high-N testing regime, ensure that potentials of UK wheat varieties are best expressed at high levels of N nutrition, and grain protein contents are maximised.

Table 9. Comparison of normal amino acid contents of wheat proteins (Dubetz et al., 1979) with those regarded as ideal in pig diets.

Composition of Ideal Proteina

Albumin & Globulin Glutenin Gliadin

Content in wheat protein 31% 29% 40%Amino Acid g/100g proteinLysine 7.0 4.9 1.7 0.7Histidine 2.3 2.4 0.8 1.8Arginine - 6.1 3.9 2.0Aspartate - 7.8 4.7 2.6Threonine 4.2 3.8 2.8 1.7Serine - 4.1 3.9 2.9

17 Lysine, methionine, trpytophan and threonine, depending on the species of plant and animal concerned.

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Glutamate - 23.7 38.4 42.3Proline - 8.6 11.0 15.0Glycine - 4.4 4.4 1.6Alanine - 5.1 3.0 1.8Methionine+Cystine 3.5 4.6 2.7 3.7Valine 4.9 6.2 4.1 4.2Isoleucine 3.8 3.4 3.6 3.8Leucine 7.0 7.2 7.3 6.6Phenylalanine+Tyrosine 6.7 7.6 8.9 8.8

a for pigs, from Fuller and Chamberlain (1982).

In physiological terms, protein deposition in grain occurs at the expense of starch deposition; protein is transferred from the photosynthetic canopy to the grain to form grain protein, and more energy is required to synthesise protein than to synthesise starch (Sinclair & de Wit, 1975). In terms of non-ruminant nutrition, wheat protein is generally low in essential amino acids (EAAs), and the greater the protein concentration, the poorer is the EAA content. Wheat grain proteins can be separated into those from the germ and bran (mainly albumins and globulins) which have modest EAA levels relative to non-ruminant requirements, and those from the endosperm (mainly glutenins and gliadins) which have poor and very poor (respectively) EAA levels relative to non-ruminant requirements (Table 9).

The protein concentration in wheat grain and other cereals is highly dependent on the N supply to the crop, and it is primarily the prolamines (called gliadins in wheat, and hordeins in barley) that respond to crop nutrition (Figs. 3 and 4). Thus the EAA level decreases significantly as crop nutritional status increases. Clearly, the prolamines in cereal grains are acting as storage compounds, in that they respond disproportionately to the crop’s supply of nitrogen, and also they act as a substrate for embryo growth during germination (Folkes 1951). There is a limit to the degree to which prolamines can be reduced without affecting the viability of seed in germination, however, this limit appears to be quite low (Naylor, 1993).

0

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Figure 3. Effect of increasing fertiliser N application on concentration of protein fractions in wheat grain (after Dubetz. et al., 1979).

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Figure 4. Effect of increasing fertiliser N application on concentration of protein fractions in barley grain (Sylvester-Bradley, 1979).

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Figure 5. Responses in grain yield (upper line) and protein concentration (bold line) of winter wheat to increasing levels of applied N (mean of 68 trials on clay soils in East Anglia). Diamonds indicate optima at 170 kg/ha N (N price = 5 x grain price) and 85 kg/ha N (N price = 18 x grain price). Also shown (small circles) is the response of leachable N (soil mineral N), taken from Bhogal et al. (2000)

Using this typical curve, it can be calculated that the price of fertiliser relative to grain would have to triple (or more) if the economic optimum amount of fertiliser N were to be halved. It is estimated that halving of N applications would reduce the mean grain protein concentration from 9.8% to 8.3% (87% DM basis).

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b.

7 9 11 13 15protein content (% in grain at 86%DM)

Figure 6. Frequency of grain protein contents in commercial fields of (milling) varieties of wheat at the harvests of 1988 and 1989.

This analysis indicates that there may be significant advantages to the livestock industry of reducing the protein concentration of feed wheat. Low protein contents should not only relate to increased energy contents, but also to greater concentrations of EAAs in the protein. It seems probable that protein contents of feed wheat could be reduced, hence also reducing that of the total feed, without reducing livestock performance and hence the value of the grain. (In addition, there is no reason to believe that use of wheat by ruminants would be adversely affected by a higher starch and reduced protein content.) There are several ways in which protein content of feed grains might be reduced:

a) The total quantity of fertiliser N applied to cereals could be constrained, by regulation, taxation or the like. This would be commercially damaging since grain yields would be significantly restricted on most land. The response of wheat yield and N content (grain protein = grain N x 5.7) to fertiliser N is shown in Figure 5.

b) Imprecision in the use of fertiliser N could be exploited by feed compounders, if they used N analysis on intake to discriminate between high and low protein lots. An example of the large variation in protein content between commercial samples of wheat is shown in Figure 6. (This figure shows variation for milling varieties; variation for feed varieties is likely to be at least as large because there are no market criteria for protein.) This might be adopted by a minority of feed mills on a short-term basis at little extra cost (except in the logistics of grain analysis and supply). However, once demand for low protein grain (= high-energy grain) became significant, a price differential would develop, and could not be sustained unless tangible commercial advantages became available to the feed industry.

c) It has proved possible, for instance by mutagenesis, to markedly reduce the capacity of new genotypes of maize and barley to form prolamines, and thereby to increase the proportion of EAAs in grain protein (Mertz, 1964; Munck 1972). These rather crude attempts at grain protein manipulation have been associated with disruption of normal endosperm formation and thus reductions in grain yield. Now that more accurate genetic analysis is possible, it seems likely that new genotypes could be developed with reduced capacity to form prolamines but without the deleterious effects on grain yield that were found previously. There do not appear to have been such attempts to reduce grain protein in wheat thus far. However, with the dominance of wheat over other feed cereals in the UK, the challenge appears to be one of genetically reducing protein contents of the grain storage tissues without affecting their capacity to store starch.

d) Breeding for reduced protein is clearly a long-term option, and one for which the full environmental benefit would not accrue unless the same varieties were also bred to take up significantly less N into their canopies; about 90% of final N uptake in conventional wheat

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varieties occurs before grain formation. It is initially used to form the photosynthetic canopy of stems and leaves, and is only subsequently redistributed to the grain when the canopy senesces. Thus a reduction in grain protein content would not, of itself, reduce requirements for fertiliser N; the two traits of low grain protein and low canopy N must be combined in the same genotype if major benefits are to accrue.

Oats have traditionally been used for feeding to cattle and sheep, although their lower energy value relative to barley or wheat has tended to restrict their use in intensive systems of production. A report commissioned by MAFF, Scottish Office, MDC and MLC highlighted oats and naked oats amongst the cereals as having important potential for improving protein supply (ENTEC, 1997). The quality of oat protein is superior to that of wheat and barley, and complements that of peas and beans. As much of the protein is in the form of globulins, increasing protein does not depress levels of essential amino acids as occurs in wheat and barley. Recent oat breeding programmes, funded by Defra and the HGCA, have focussed on developing oats with higher energy and protein contents, but it remains to be seen whether these can compete with other cereals.

Rapeseed meal

Oilseed rape (OSR) is now the third most important arable crop in the UK after barley and wheat, with >500,000 ha under cultivation. Most U.K farmers grow the higher yielding winter crop. It is grown principally for the oil contained in the seed, which is used in cooking oils or margarine, with the meal being used for animal feed. Current varieties of rapeseed are low in erucic acid and glucosinolates (also known in N America and Australia as Canola meal). According to marketing specifications, it must contain 35% protein, a maximum of 12% crude fibre, and a maximum of 30 moles of glucosinolates per gram. There is increasing interest in the use of rapeseed oil for industrial purposes, including the growing of high erucic acid rape (HEAR). The principal end use erucic aid is as a lubricant in injection-moulded plastics and polythene manufacture. There is no evidence that meal derived from HEAR is any less nutritious than conventional meal provided that extraction of erucic acid has been satisfactorily achieved.

The amino acid content of the meal is similar to that of soybean meal, and to an extent it can therefore replace some of the soybean meal in livestock diets. However the main reason for the dominance of soyabean meal as a protein ingredient is its relatively high protein content of 44-46%. In contrast, rapeseed meal has a lower protein level (34-38%); this is particularly important in formulating diets for high producing stock, when nutrient concentration takes on greater importance. It also has a higher fibre content, which means that it has a slightly lower level of energy content relative to soyabean meal. Rapeseed meal is also considered by some to adversely affect meat quality (flavour) when used in poultry finisher rations.

OSR meal accounts for about 10% of the N in compound feeds. Most of this is from UK-grown, although small quantities are available from imported rapeseed crushed in the UK.

It is now recognised that compared with burning fossil fuels, the use of biofuels can contribute towards reducing emissions of carbon dioxide. A report by Sheffield Hallam University18 found that net savings of 71% in carbon dioxide emissions could be realised by replacing ultra low sulphur diesel with biodiesel produced from oilseed rape. Agronomists have suggested that up to 1.6 m ha of oilseed rape could be grown, representing an increase of almost 400% on current levels. Using current production practices, expansion on this scale could have major environmental implications. Oilseed rape can theoretically be grown using certain “modified practices” (Mortimer et al., 2003) including reduced applications of fertilisers and burning the straw to provide heat at the processing plant. Rigorous application of these practices could double the energy efficiency of this process, and reduce the impacts of cultivation on natural resources, although it would result in lower yields. However, it is reasonable to assume that the amount of rapeseed meal available for use as livestock feed would increase substantially if biodiesel production increases.

18 Evaluation of the comparative energy, global warming and socio-economic costs and benefits of biodiesel, N. D. Mortimer, P. Cormack, M. A. Elsayed and R. E. Horne, Sheffield Hallam University, January 2003.

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Peas and Beans

The UK production of peas (Pisum sativum) and beans (Vicia faba) is about 770 kt grain (containing about 40 kt N), compared to the 1 500 kt of imported soya (containing about 110 kt N), and the 15 Mt home-grown cereals used in feed (providing about 247 kt N). They are used predominantly in compound feeds, where they contribute <2% of the protein in these feeds. They therefore currently make only a small contribution to the N supply to UK livestock.

The protein concentrations of peas (22%) and beans (26%) are relatively low compared to soya beans (37%) and lupins (35%). There have been problems in breeding for both improved yield and improved protein content in peas: yield and protein appear to be negatively correlated (Slinkard, 1980). Legume grain protein quality is better than cereals, but still is open to improvement (Millerd, 1975). Because of their lysine content, peas are a good complement to cereals. However, they are deficient in sulphur amino acids and tryptophan.

The incorporation of new agronomic traits such as topless type, hybrid vigour and winter adaptation into new cultivars of beans, and the elimination of both tannin and glucopyranosides, have provided a crop and product that is more attractive to growers and the animal feed industry. A large EC-funded research project19 is currently in progress to identify opportunities for increasing grain legume production and utilisation in Europe, and in particular develop new genetic, genomic, post-genomic and bioinformatic tools to improve and sustain grain legume seed production and quality. The project is due to be completed in 2008

Linseed meal

Linseed meal is obtained after grinding the flakes, cake, or chips that remain after removal of oil from flaxseed by mechanical or solvent extraction. It is palatable, mildly laxative, and contains somewhat less energy than soybean meal and is higher in fibre (ADF). It is a relatively high N feed (~50 g N/kg DM) with degradability similar to soybean meal. There are generally not thought to be any limits to the amount that can be fed, other than those imposed by total protein and protein degradability specifications. However, Mansbridge (1997) reported that intakes by high yielding dairy cows receiving compounds containing 17% linseed meal were lower than for other protein supplements, suggesting that the cows found the diet containing linseed to be less palatable and/or digestible.

There are no data available from official statistics on the amount of linseed meal used in the manufacture of animal feeds, but quantities are likely to be very small in relation to other protein sources. Lupins

Lupins (Lupinus spp.) are grain legumes, the seeds of which contain relatively high protein contents (30 to 40% DM). Wild lupins, and those used in horticulture, are poisonous, containing high levels of toxic alkaloids. Other potentially toxic constituents include enzyme (trypsin) inhibitors and biochanin A.

Recently, determinate varieties have been bred which are both low in alkaloids and are suited to cultivation under UK conditions. In the UK, the species with the greatest potential protein yield is white lupin Lupinus albus L. More recently dwarf determinate genotypes have been developed which have superior over-winter survival (Milford and Huyghe, 1996).

Current lupin production in the UK comes from c.7, 000 ha (mostly spring sown) producing 17,500 tonnes, and equivalent to about 17,000 tonnes of soya meal. Siddons et al. (1994) calculated that 130,000 ha were available annually for lupin production in England and Wales. This area is only slightly smaller than the average annual total area of peas and beans.

Lupins are characterised by proteins that are poorly protected against microbial protein in he rumen, and are therefore of relatively moderate biological value. Studies funded by MAFF and the MDC have confirmed that lupins may be used as an alternative to soyabean meal for beef

19 EC Framework 6: The Grain Legume Integrated Project

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cattle (Moss et al., 1997) and growing lambs (Kung et al, 1991). However, Allison et al. (2001) reported that complete replacement of soya bean meal with lupin meal in compounds for high yielding dairy cows resulted in a reduction in dry matter intake and milk production. For pigs and poultry, the nutritional value of lupins is limited by their content of non-structural polysaccharides. However, enzyme supplementation can improve the nutritional value of the feeds, and enzyme-treated lupins have been fed successfully to broilers as the sole feed. However, the relatively low energy content of lupins limits their inclusion in non-ruminant rations to about 5%.

The economics of growing spring lupins for combining is questionable unless yields can be improved and initial seed costs reduced (Landrock-White, 2003). The value of the crop varies with the price of soya, ranging from about £105 to £130/tonne in 2002 for feed use, with premiums being paid for seed crops. The removal of area aid payment is likely to make the economics of growing the crop even more tenuous. Even in 2002 (with area aid payments) most farmers growing winter lupins decided that they were not economic to grow because of the number of crop protection chemicals required.

Summarising the options for modifying the non-forage crops fed to livestock, wheat appears to offer the best prospect of making a significant impact. There are inherent reasons why husbandry or market manipulation would be counter-productive economically. Thus breeding offers the best approach, targeting jointly low protein and high energy content with maintained yield. A research project with these objectives was initiated in 2004 under the Sustainable Arable LINK scheme; it is entitled ‘Genetic Reduction of Energy use and Emissions of Nitrogen through cereal production: G R E E N grain’ (Project LK0959). In this project it is envisaged that the resultant grain will have a protein content and composition similar to those from crops which have received no fertiliser N i.e. about 8% on a dry basis; fertilised feed wheat varieties currently have about 11% protein on a dry basis. It is expected that varieties identified, or varieties that are bred from the materials developed, will both provide end-users with grain of enhanced value, and also growers with better returns. This is partly because availability of high-energy varieties will expand the market for UK wheat, particularly for bioethanol production, partly because high-energy wheat will need less fertiliser (and other inputs) than conventional wheat, and partly because on-farm energy use and downstream pollution will be reduced. It is expected that there will also be significant benefits to the distilling and livestock industries, both in terms of cost savings, and reduced N pollution.

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Section 7: Feed selection and management strategies

Since the amount of N excreted in by livestock is a reflection of the imbalance between requirements and supply, the most effective strategies for improving N utilisation will be those that match the supply to demand. Because of the differences between ruminants and non-ruminants both in their requirements for and digestion of protein, different strategies to reduce N excretion have had to be devised for each species type, and these are described below.

Pigs and poultry

Nitrogen utilisation efficiency (NUE) by pigs and poultry is generally low. In growing pigs, only 30 to 40% of dietary N is converted into lean tissue (Jongbloed and Lenis, 1998; Lee at al., 1998, Han et al., 2001), while for laying hens NUE of 35-38% has been reported (Leclercq, 1996). Utilisation efficiency varies with physiological status, age and gender of animal, and the energy supply. For example, average efficiency for N retention is the lowest in sows (23%) intermediate in growing pigs (34%) and the highest in weaners (48%) (Dourmad et al., 1999). Whittemore et al., (2001) have estimated that more than a quarter of these N excreted may be attributed to a failure to maximise production and to optimise efficiency by correctly matching dietary protein quantity and quality to those required by the pig as it grows.

A number of feed and livestock management strategies have been identified for improving N utilisation and reducing N excretion by pigs and poultry. Their potential for reducing N excretion have been summarised for poultry (Table 10) and pigs (Table 11).

Table 10. Estimated reduction (%) in N in manure by manipulating the diet and the feeding program in broilers (Mateos, 2005)

Use of synthetic amino acids 20-25Phase feeding 10-15Reduce safety margins 10-20Selection of highly digestible ingredients 5Reduce feed wastage 2-8Formulate on digestible amino acids 2-5Enzymes (carbohydrases) 2-5Growth promoters & additives 2-5

Table 11. Measures to reduce the excretion of N by pigs (Hemke, 2002), based on 1995 levels.

Effect on N excretionKg N/sow/year Kg N/growing pig/year

Average level 1995 30.8 13.1Intake (sow/year) – 100 kg 10%Piglets/sow/year +1 1%Average daily gain +10 g/d +1.5Feed conversion –0.1 - 5%3-phase feeding - 4%Rearing by separate sexes - 2%

Many of these measures have been adopted UK pig and poultry producers, although the extent to which they are used is unknown since there is no national survey of feeding practices (as there is for fertiliser use). However, it may not be unreasonable to speculate that the greatest

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improvement in N utilisation is likely to come from the use of synthetic amino acids to provide an optimum amino acid balance.

The use of industrially produced amino acids in animal feeds is not new. DL methionine was produced by chemical synthesis in the 1950s and 1960s for inclusion in poultry feed, while L-lysine production by fermentation began in the 1960s in Japan, followed by L-threonine and L-tryptophan in the late 1980s. The adoption of modern production techniques has revolutionised the manufacturing process, and has significantly reduced the costs of amino acid production. More recently, the use of genetically modified microbial strains has substantially improved production efficiency and competitiveness. The economics of production has therefore changed dramatically, providing much greater opportunities for synthetic amino acid use.

On of the underlying objectives of this study is to examine how improvements in protein use from animal feeds may enhance feed N utilisation. The increased substitution of synthetic amino acids for plant protein could provide greater efficiency and effectiveness of protein utilisation, but the cost effectiveness of their use needs to be continually assessed.

It has been estimated that the incorporation of one tonne of L-lysine hydrochloride could replace 33 t of soybean meal. Or, if 550,000 t of L-lysine hydrochloride is used globally, it could replace 18 million tonnes of soybean meal, representing about half of the USA soybean meal production (FAO, 2002)20. There is therefore potential for considerable impact on current protein supply trade and the types of protein currently used. It is also argued that greater synthetic amino acid use could reduce nitrogen pollution from animal wastes, as a result of better and more efficient nutrient utilisation. Future developments of synthetic amino acid production are likely to include synthetic isoleucine, valine and arginine, thus extending the range of amino acids available for use in feeds. The degree of use would be mainly determined by the increased in productivity relative to the cost of the synthetic amino acids.

The development of feeding techniques for improving N utilisation, and in particular the use of synthetic amino acids, will only be effective where both the amino acid content and availability in other feedstuffs is known, and where the amino acids requirements for the particular growing stage or physiological status are well defined. Modelling techniques to describe the amino acid requirements of growing pigs, broilers and layers have been established, and estimates of the amino acid requirements obtained (NRC, 1998; Whittemore et al., 2003; van Milgen et al. 2005). However, possible adverse effects of low protein diets on carcass composition remain a concern, particularly in the pig industry, and further research is necessary to provide producers with the necessary confidence to implement such a strategy.

There can be considerable variation in the protein and amino acid content of feeds. Although the technology exists to measure the amino acid content of feeds, it is an expensive and time-consuming analysis. As a result, many feed formulations are based on average values, often with a safety margin added to ensure that the amino acid requirements are met. The net effect of this is that many diets are formulated that provide more N than required, with the surplus N being excreted.

Control of feed wastage is obviously an important consideration when trying to optimise utilisation and minimise environmental pollution. Wasted feed typically mixes with excreta to increase nutrient content. In systems with poor design or management of feed presentation, wastage in excess of 10% is not uncommon, and attention to this issue is the most cost-effective way to both improve feed efficiency and reduce nutrient loss. Certain systems such as the feeding of meal result in large increases in feed wastage when compared to pelleted feed (Vanschoubroek et al. 1971).

Ruminants

As discussed in Section 5 (page 18) the NUE by ruminants is generally low, and usually less that 30%. A number of measures have been identified that may contribute to an improvement in NUE and reduction in N excretion.

20 www.fao.org/ag/aga/workshop/feed/execsummary.pdf

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Feeding according to protein requirements

The protein requirements for dairy cows have been published by a number of authorities (e.g. AFRC, 1993; NRC, 2001). These are usually described in terms of rumen-degradable and digestible undegradable protein. A number of factors determine the ability of a diet to meet these requirements, the main ones being the rate and extent of protein degradation in the rumen and the supply of energy to the rumen micro-organisms to utilise the degraded N. Despite considerable research effort, rapid and reliable methods for quantifying these characteristics in individual feeds or complete diets are imprecise. Improvements in predicting feed protein degradability and microbial protein synthesis would significantly improve the scope for diet formulation to improve NUE.

Given the importance of protein in maximising the feed digestibility in the rumen (Oldham, 1984), and the fact that increasing dietary protein above apparent requirements is frequently associated with increasing DM intakes, dairy farmers are understandably reluctant to reduce dietary protein contents.

Protein requirements change through the course of the lactation, reflecting the needs for milk protein synthesis, foetal growth, and replenishment of body protein that may have been mobilised during early lactation to supply additional nutrients. In practice, dairy cows are usually managed in groups, based on stage of lactation or milk yield, and in this context many dairy farmers practice ‘phase feeding’ similar to that used for non-ruminant livestock production. However, within groups there may be significant differences between individual cows in their requirements for digestible protein.

Substitution of grass silage with alternative forages.

As described above, the main reason for the low utilisation of grass silage-N appears to be an imbalance in the supply of degraded N relative to energy supply to the rumen micro-organisms (Beever et al., 1986). An associated problem with silages is that the ensiling process effectively converts most of the readily available energy (present as carbohydrates) to lactic and volatile fatty acids that yield little energy in the rumen for microbial synthesis. This, coupled with the changes in the N fractions as a result of ensiling, results in a very low efficiency of microbial protein synthesis, particularly when compared with other forages. Givens and Rulquin (2004) have reported mean efficiencies of microbial protein synthesis21 for maize silage of 48.4 g microbial N/kg OMADR, compared to a value of 30.1 for grass silage. The higher efficiency on maize silage is most likely due to improved energy supply in the form of the starch present in maize silage. This may explain the production responses observed in the ‘MiDAS’ study, in which maize-based diets were the most effective strategy to reduce N excretion from the dairy cow. Whole crop cereal silage, on the other hand, was not a satisfactory alternative to maize in these studies (Withers et al., 1999). The use of alternative forages (to grass and grass silage) to improving NUE is considered below.

Maize silage

The inclusion of maize silage in grass-silage based diets for lactating dairy cows has been shown to increase food intake, milk yield and milk protein content (Pain & Phipps, 1975; Phipps et al., 1988; Phipps et al., 1995). Moreover, replacing grass silage with good quality maize silage (containing 200-250g starch per kg/DM) has the potential for increasing NUE, and there appears to be a strong correlation with starch levels up to 30%. An improvement in NUE from 29.9 to 32.3% in dairy cows fed a 3:1 maize and grass silage mix was associated with a decreases in urinary N output, which was linearly related to forage starch content (Cammell et al., 2000). Comparing grass silage with maize silage as forages for lactating dairy cows, Valk (1994) observed improvements in NUE (N milk/N intake) by 50%, from 0.18 (grass silage) to 0.27 (maize silage). It was concluded that the improved NUE from maize silage was most likely due to an improved NSC:N ratio. Delaby et al., (1995) calculated that a dairy cow producing 6,000 kg milk/annum would lose 13.3 and 18.2 kg N/kg milk N produced on maize and grass silage based diets respectively. Extrapolated to the entire British dairy herd, this would equate to a reduction in

21 Expressed as g of microbial N synthesised per kg organic matter fermented in the rumen.

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N excretion of approximately 213 kt N annually if maize silage rather than grass silage were fed. On the basis of a review of research on the potential of maize silage as a feed for dairy cows, Fitzgerald et al. (1998) concluded that a 50:50 mix of maize and grass silage is about the optimum for dry matter intake and milk production.

Incorporation of maize silage into beef cattle diets can enhance production. Beef cattle finished on iso-nitrogenous diets based on maize silage had improved DMI, daily liveweight gains, better feed conversion ratios, a 28% improvement in NUE (N carcass/N intake) and finished 44 d earlier when fed the maize silage compared to the grass silage diet. Furthermore, killing out percentages, carcass weights, muscle accretion rate and depth were all significantly enhanced for the steers fed the maize silage diet (Bryant and Beever, 2000).

Whole crop cereals

There has been increasing interest in recent years in harvesting cereal crops at an immature stage and conserving them as silage, as an alternative or in addition to grass or maize silage. In order to improve the digestibility of the crop, particularly for more mature crops, sodium hydroxide or urea may be added at the time of ensiling. For health and safety reasons, the latter is to be preferred. While much of the urea N is lost to the atmosphere when the silage is fed, the urea N that remains in the silage contributes to the provision of rumen degradable N. Although the efficiency of microbial protein synthesis on whole crop cereal diets is better than for grass silage the conversion of urea-N to product (milk or meat) is likely to be low (Givens and Rulquin, 2004).

Forage legumes

A number of studies have examined the role of legume forages – either as the sole forage or in conjunction with grass silage. An EU-funded study22 concluded that forage legumes could play an increasing role in developing more sustainable farming practices. Because they capture nitrogen from the air, they reduce the need for inorganic fertilisers. In addition, using these crops as silage can also reduce the need for high-protein concentrate feeds on the farm. The results of this study have confirmed that silage made from legumes, or from legume-grass mixtures, outperforms silage made from grass alone, and that using silage made from forage legumes can significantly increase the profitability of dairy systems. At a farm level, therefore, the use of forage legumes may improve NUE. However, N intakes on legume-based diets tend to be higher than on grass silage-based diets, resulting in lower NUE when calculated at an animal level (Dewhurst et al., 2003). In a study involving four different forage legumes, the NUE for milk from four forage legumes were significantly lower than that from grass silage. Mixing legume silages with grass silage resulted in NUE intermediate to those of the pure legume silages (Bertilsson et al., 2001). When WC silage (WCS) was combined with maize silage (MS) (WCS20:MS80) higher milk yields and 17% lower N excretion was observed compared with grass silage. However, when fed at a ratio of 40WCS:60MS, N outputs were 10% higher compared to a ration containing grass and maize silage in a 60:40 ratio (Dewhurst, 2004). Clearly the balance of forages is critical in achieving optimum NUE.

The combination of high levels of N leaching from forage legumes and their low NUE by livestock suggests that they may not be suitable as the major portion of the forage ration for ruminant systems designed to maximise NUE and minimise the environmental burden. Their judicious admixture with high WSC/low N forages may be more appropriate in this regard. However, greater NUE can be obtained from legumes containing substances that reduce N degradation in the rumen, as described above (Section 5a(iii)).

Supplementation with synthetic amino acids

Optimising the supply of individual amino acids by using synthetic amino acids has been common practice in the poultry industry for over 35 years and in pig nutrition for the last 25 years. Attempts to identify requirements for, and responses to supplementary synthetic amino acids have been the subject of a number of reviews (Buttery and Foulds, 1985; Rulquin and Verite, 1993; Sloan, 1997). It is generally accepted that methionine and lysine are the most limiting for milk synthesis (Clarke,

22 Legumes for silage in low input systems of animal production (LEGSIL)

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1975; (NRC, 2001), and attention has therefore focussed on the increasing milk protein synthesis by supplementing diets with these synthetic amino acids.

Due to problems in predicting the extent to which dietary proteins are degraded in the rumen, it has been difficult to identify situations in which positive and cost-effective responses to supplementation with synthetic amino acids will be achieved. Since synthetic amino acids are themselves subject to degradation in the rumen, methods have been developed to protect the amino acids from this degradation. Even with rumen-protected amino acids, however, responses to supplementation have been variable. A number of studies (reviewed by Sloan, 1997) have shown that supplementing with methionine and lysine on grass or maize silage-based diets resulted in increases in milk protein synthesis. However, results of other studies have been less conclusive (Polan et al, 1991).

Diet supplementation with readily fermentable carbohydrate

Rumen micro-organisms require a readily degradable supply of N and energy to maximise EMPS. The energy needs to be supplied in the form of rapidly available sugars and/or starch and other non-structural carbohydrates (NSC). As discussed above, use of HSG can help improve the energy:N ratio and result in improved NUE without recourse to supplements.

The inclusion of maize silage in the diet also has the effect of improving the energy:N ratio due to its low N (1.6 g/kg DM) and high starch (200-300 g/kg) contents. The inclusion of maize silage has been shown to improve NUE utilisation in beef cattle (e.g. Cottrill, 1981; Bryant and Beever, 2000) and dairy cows (Valk, 1994; Fitzgerald et al., 1998a, b; Cammel et al., 2000).

The effectiveness of sugars and starch-rich concentrate feeds is less clear. In theory, supplementation with these should enhance EMPS, and there is some evidence that it does (eg O’Mara et al., 1997). However, the effects have not been consistent; Broderick and Radloff (2004) recently reported that with increasing levels of sugar (as molasses) in the diet there was a linear increase in dry matter and digestibility of dry matter, but no effect on yield of milk or protein. It appears that diets providing higher concentration of rumen fermentable fibre, rather than NSC, are most likely to enhance transfer of degraded N and microbial N into milk protein (Hristov and Ropp, 2003).

Microbial protein synthesis is a dynamic process, and therefore a logical extension to this theory is that NUE should be improved where there is a synchronous delivery of rapidly degradable protein and energy to the rumen. A number of studies have been undertaken to test this theory (e.g. Johnson, 1976; Sinclair et al., 1993). However, results from studies to date have been equivocal (e.g. Witt et al., 2000; Richardson et al., 2003). Nevertheless, there is some evidence that ad libitum feeding of total mixed rations rather than meal feeding improves NUE (Chamberlain and Choung, 1995) because it prevents significant asynchronous supply of N and energy to the rumen. If this is so, then many UK dairy farmers are already making a contribution to improving NUE since complete diet feeding is now widely practised.

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Section 8: Scenarios for improving dietary N utilisation by livestock

This section attempts to quantify, through a series of scenarios, the effects on dietary N utilisation and excretion that might be expected as a result of adopting some of the strategies described above.

(i): Scenarios for improving dietary N utilisation by pigs and poultry

(a) Using an ideal protein approach

Lee & Kay (2003) describe an experiment in which the protein content of diets fed to growing and finishing pigs is altered from conventional (mean 23.3%) to medium (mean 21.7%) and low (<20%) levels, whilst levels of essential amino acids (EAA’s) are maintained from synthetic sources. N excretion was markedly and significantly reduced by both low protein treatments, but livestock performance was also reduced by the lowest protein treatment. The conventional and medium diets have therefore been adopted here to quantify the impacts on a whole farm basis of adopting ‘ideal protein’ diets (Table 12).

Table 12. Effects of dietary manipulation, according to Lee & Kay (2003), on N emissions and net farm balances, both nutritional and financial. The hypothetical farm has 200 ha arable land growing wheat and oilseed rape, and 5,000 pig places.

Nitrogen (kg/ha) Costs & returns (£/ha)Normal Scenario Normal Scenario

effect effectAtmospheric input 50 0Fertiliser inputs 191 2 £63 £1Crop exports 93 -6 £331 -£22Imported feed 144 -48 £288 -£76Animal exports 104 -2 £2,194 £0Nitrate leaching 54 0Manure emissions

Housing 6 -2Storage 6 -2Spreading 65 -16

Total emissions 131 -19Net farm balance 58 -19 £2,174 £53

Considering the conventional scenario, the N inputs to the farm are fertiliser, imported feeds, and atmospheric deposition; these total 385 kg/ha N. Crop & stock exports total 197 kg/ha N, and N emissions total 131 kg/ha N. The remaining 58 kg/ha N contributes to the N status of the soil. The main outcome of manipulating the pigs’ diet is to reduce the amount of N in imported feeds; when translated through manure output, this benefit is shared equally between reduced N emissions and a reduced effect on soil N. On a financial basis, the majority of the farm’s income comes from livestock sales. The net effect of dietary manipulation is positive by £53/ha, largely because the reduced expense on imported feeds was greater than the reduced crop sales.

(b) Replacing wheat with maize

The second scenario examines the effect of replacing home-grown wheat with imported maize (Table 13). Clearly the cost of imported maize is greater, so the financial effect (-£122/ha) could not be sustained under current commercial conditions. However, the point of this scenario was to explore the effect of including a higher energy / lower protein cereal than wheat in the ration: the wheat here was assumed to have 10.9% protein whilst the maize was assumed to have 8.6% protein. Feed formulation only gave slightly different protein contents for the two scenarios (21.2% & 20.3%), averaging the contents for growers and finishers. Because of this, the effects on N excretion and N emissions were small.

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Table 13. Effects of feeding maize, rather than home-grown wheat on N emissions and net farm balances, both nutritional and financial. The hypothetical farm has 200 ha arable land growing wheat and oilseed rape, and 5,000 pig places.


effect effectAtmospheric input 50 0Fertiliser inputs 192 0 £63 £0Crop exports 70 57 £247 £197Imported feed 112 51 £275 £319Animal exports 90 -3 £2,194 £0Nitrate leaching 54 0Manure emissions

Housing 6 0Storage 5 0Spreading 62 -2

Total emissions 127 -3Net farm balance 66 0 £2,102 -£122

Clearly the most effective way of reducing N emissions through feeding will be to achieve the greatest reduction in total dietary protein, without affecting livestock performance.

(c) The Low N Grain concept

The third scenario (Table 14) assumes that the Low N Grain concept will be realised: fertiliser N inputs to wheat can be halved and wheat protein content can be reduced from 11% to 8% without affecting grain yield.

Feed formulation for pigs using these two wheat types gave mean (of growers and finishers) dietary protein contents of 17.3% and 16.8%. Fertiliser inputs were not quite halved, largely because fertiliser inputs for the quarter of the farm in oilseed rape was unchanged. Crop exports and feed imports were increased because less wheat could be included in the diets with Low N Grain. Nitrate leaching due to cropping was decreased by 20% and the effect on soil N was marked because of the lower fertiliser usage, but N emissions from manures are little affected because the protein in the diet was only marginally reduced. Thus the main environmental (and financial) benefit of feeding Low N Grain to pigs arises through the reduced use of fertiliser rather than through reduced manure production.

Table 14. Effects of genetically halving fertiliser requirements of wheat and reducing grain protein from 11 to 8% (the Low N Grain concept) on N emissions and net farm balances, both nutritional and financial. The hypothetical farm has 200 ha arable land growing wheat and oilseed rape, and 5,000 pig places.


effect effectAtmospheric input 50 0Fertiliser inputs 193 -82 £64 -£27Crop exports 49 -3 £177 £17Imported feed 90 19 £273 £30Animal exports 101 0 £2,194 £0Nitrate leaching 54 -11Manure emissions



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A feed formulation for broilers was also undertaken using these two wheat types (Table 15). This gave dietary protein contents of 21.5% and 20.4% respectively. Once again crop exports and feed imports were increased and N emissions from manures were not much affected because the protein in the diet was only marginally reduced. Also the main benefits arise through the reduced use of fertiliser rather than reduced manure outputs.

In describing the Low N Grain scenarios it became evident that the principal issue governing the successful reduction of environmental effects was in the assumptions made in least-cost ration formulation. The programmes used to do this were highly sensitive to small changes in the composition of ingredients, yet the data used for composition was taken from standard tables and often these were known to be subject to significant variation, due both to growing conditions and to genotype. For example, in the case of broilers, the reduced level of protein in Low N Grain was compensated by increased inclusion of soya. But because soya is relatively deficient in sulphur-containing amino-acids, synthetic methionine was required, at significant cost.

Table 15. Effects of genetically halving fertiliser N requirements of wheat and reducing grain protein from 11 to 8% (the Low N Grain concept) on N emissions and net farm balances, both nutritional and financial. The hypothetical farm has 200 ha arable land growing wheat and oilseed rape, and a unit producing 60,000 broilers per cycle.


effect effectAtmospheric input 50 0Fertiliser inputs 191 -82 £63 -£27Crop exports 76 -13 £295 £4Imported feed 127 5 £460 £14Animal exports 71 0 £1,763 £0Nitrate leaching 54 -11Manure emissions



(d) Discussion

It is almost axiomatic in the way that our model was set up (viz. the assumption that livestock performance does not change with diet) that N emissions will be almost entirely dependent on protein intakes. The experiments by Lee & Kay (1993) showed that this assumption underestimates the effect of protein level on N excretion. Not only was there a reduction in the amount of N excreted, but the proportion of urinary N was reduced and the volume of the N excreted was also reduced.

The modelling exercise has clearly shown that, in seeking to reduce protein intakes by UK non-ruminant livestock, one of the main issues is in the confidence, or otherwise, that livestock nutritionists have in reducing the protein contents of livestock diets. Confidence does not appear to be strong because:

The number of possible permutations in feed formulation is huge and, because livestock feeding trials are very expensive, few of these formulations have been tested experimentally.

The precision of measures of livestock performance is only modest, and less than the differences that affect commercial performance in modern, large and intensive production units.

There are bound to be differences in requirements between livestock types (different strains, ages, management systems, products, etc.) which add to the uncertainty. To an extent, known differences in performance-attributes of livestock outputs (e.g. meat vs. milk) can be

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used to predict differences in their nutritional requirements. However, differences in efficiency of digestion and feed conversion are less easy to predict.

There are more essential amino acids (EAA) provided in feed proteins than have been thoroughly tested for livestock responses; major EAAs (lysine, methionine-cystine, threonine) have been tested, but there is uncertainty about requirements for some of the less important EAA’s, and possible effects of deficiencies on growth.

Because of the cost and time associated with amino acid analysis of feeds, many commercial feed manufactures rely on ‘book values’ for the AA content of feeds or direct predictions from the N content. Because of the variation that is known to exist, formulator’s tend to err on the side of caution in their estimates of the AA content of feeds.

It should be remembered that the so-called ‘protein feeds’ are also a valuable source of energy. Thus, other than the environmental effects, which have slight commercial significance, the greater price of high protein ingredients is the only incentive to minimise protein. The response of feed formulators to the uncertainty surrounding both requirements and supply is to allow considerable oversupply of protein, so that the risk of under-performance is minimised.

For any nutrient, there is a degree of uncertainty surrounding both the composition of the feed materials and the requirements of livestock. Uncertainty relating to feed composition has been reduced considerably in recent years with the development of more rapid, accurate and cost effective methods of analysis. Attempts have been made to develop near near-infrared reflectance (NIR) and near infrared transmittance (NIT) spectroscopy calibrations for amino acids. NIR can give useable estimates of the major amino acids in most feed stuffs evaluated; these estimates are not as accurate as the standard methods of analysis, but may be acceptable for feed formulation. It is not clear to what extent these are used in the UK. More frequently, the amino acid contents are predicted from total N content of the feed or book-values are used.

There is also some debate over the N requirements of pigs and poultry. In particular, there is uncertainty over what constitutes the ‘ideal protein’. Yet least-cost diet formulation on an ideal protein basis can be influenced significantly by the ratios used (Baker, 1996). Defra, through the British Society of Animal Science, has contributed to the development of quantitative descriptions of protein required by the growing pig (Whittemore et al., 2001, 2003), but requirements for fattening pigs and sows in particular need further refinement.

The response of nutritionists to these uncertainties is to allow considerable oversupply of protein, so that the risk of under-performance is minimised. Nutritionists vary in their attitude to risk and thus to minimum protein contents. Feed formulation is very sensitive to prices of ingredients, so there may be scope for gradually imposing downward pressure on protein inclusion by taxing protein.

(ii) Scenarios for improving dietary N utilisation by dairy cows

(a) Reducing N intake

There is ample evidence that reducing N intake results in a reduction in N excretion and an increase in NUE by dairy cows. This is illustrated (right) using data from over 500 dairy cow measurements on a wide range of grass silage-based diets (Patterson, Yan and Hameleers, 2004). Similar observations have been reported by others (e.g. Kebreab et al., 2001; Broderick, 2003; Hristov, Price and Shafil, 2004).

However, reducing dietary protein content frequently results in a reduction in dry matter (DM) intake and milk yield (Gordon, 1980; Twigge and Van Gils, 1984;Christensen et al., 1993;Cunningham et al., 1996; Wu

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and Satter, 2000; Broderick, 2003; Patterson, Yan and Hameleers, 2004). For dairy farmers with a fixed milk quota intent on maintaining farm milk output, a reduction in milk yield per cow will necessitate an increase in cow numbers. The economic effects of this are illustrated below, for a dairy farmer with a milk quota of 600,000 litres (Table 16).

Table 16. Estimates of responses to changes in dietary protein, based on production data of Cunningham et al. (1996) and estimates of N excretion (Kebreab et al., 2001). Number of cows 81 85 91Annual yield (kg/cow) 7,440 7,040 6,560Dietary protein level 18.5 16.5 14.5Relative N intake 100 88 77Milk yield (kg/d) 37.2 35.2 32.8N excretion (g/day) 371 329 293Relative N excretion 100 89 79Change in profit (£)a -4,154 -9,658

a includes costs for land, labour, machinery and finance associated with additional cows (Budgeting data from J. Nix, 2004)

Although there is a 21% reduction in N excretion as a result of reducing dietary protein from 18.5% to 14.5% when calculated on a per cow basis, the reduction at the farm level is only 11% due to the extra number of cows required to maintain quota. This simple calculation also takes no account of the additional young stock that will be required. There seems to be little financial incentive for farmers to reduce the dietary protein content for cows on grass silage-based diets.

(b) The effect of energy source on NUE

A number of studies have examined the effect of different types of energy supplement on NUE, principally comparing fibre and starch-based energy sources. Based on data from these, Kebreab et al. (2001) have developed a number of equations to predict N excretion (Figure 7). These suggest that the type of supplement may influence the partitioning of excreted N between faeces and urine but has little effect on the overall amount of N excreted, or by extrapolation on NUE. They also confirm the overriding effect of total N intake on NUE. Similar studies in Sweden have shown that concentrate energy source has little effect on NUE; however, reducing dietary N content from 27.2 to 21.2 g N/kg DM (170 to 135 g CP/kg DM) increased NUE from 34% to 43% (Frank and Swensson, 2002).

(c) Changing the concentrate protein source

Section 6 (page 29) described a number of protein crops that will grow under UK conditions. The proteins in these feeds tend to be more rumen degradable than fish meal and soyabean meal (Moss and Givens, 1994), although heat treatment has been shown to reduce rumen degradability of protein without reducing intestinal digestibility in some situations (Bertilsson et al., 1994; Herland, 1996). Allison et al., (2001) concluded that fish meal and soyabean meal could be replaced with either heat treated rapeseed meal, heat treated beans or a combination of rapeseed meal, lupins and beans without any reduction in feed intake or milk yield. Feeding heat-treated lupins alone as the major source of protein led to a reduction in dry matter intake and milk protein concentration. This and similar studies (e.g. de Sousa et al., 2001) clearly demonstrate the potential for achieving lactation yields of 9,000 litres with grass silage-based diets supplemented with these home-grown proteins. To achieve similar yields with these alternative proteins, however, the overall protein content of the diet needs to be increased, resulting in a reduction in

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NUE. Moreover, before high levels of these home grown proteins can be used in dairy cow diets reliable information is required on the variation in protein quality between sources, and the effects of varieties, seasons and crop husbandry on protein quality and degradability.

Can the choice of protein feed influence NUE? Santos et al (1996) reviewed 108 feeding studies that had examined the effects of replacing soya bean meal with other protein supplements. Although most studies did not include a specific examination of protein source on NUE per se, these authors concluded that only substitution with fish meal or rumen-protected soya bean meal were likely to have any beneficial effects on NUE. No consistent improvements in milk yield or composition – and by extrapolation NUE - were obtained by replacing soya bean meal with other conventional protein sources. Most of the studies in this review were undertaken in the USA, and involving forages not commonly used in the UK. Here, a number of studies have been reported which have compared the effects of replacing soya bean meal with other protein supplements on grass silage-based diets (Mansbridge, 1997; Alison et al., 2001; Shingfield et al., 2003). These results confirm the conclusions of others (e.g. ENTEC, 1997), that it is possible to replace most or all of the soya bean meal with alternative protein sources without compromising milk production. However, in all cases the overall protein concentration of the diets was higher than in the control (soya) diets, and NUE was lower as a result of replacing soya bean meal with alternative protein feeds. Where protein degradability has been reduced without increasing the protein content of the diet, there has been little effect on the utilisation with which diet N is converted into milk N (Kebreab et al., 2001). In this study, however, reducing dietary protein degradability resulted in a significant repartitioning of N from faeces to urine as the degradability increased. These authors calculated that in the UK alone, this change due to reduced protein degradability would reduce ammonia volatilisation from dairy cows by as much as 12 kt/year. Thus, although changing protein degradability may not improve N utilisation, there may be environmental benefits from this strategy.

(d) Using synthetic amino acids

Few studies have looked specifically at the potential for reducing dietary N in combination with protected amino acid supplementation to improve efficiency of dietary N utilisation or N excretion. In one study, supplementing with rumen-protected methionine and lysine allowed protein intake to be reduced by more than 150 g/cow/day (Dinn et al., 1998). Diets were fed to high yielding dairy cows receiving a complete diet in which the forages consisted of grass and maize silages. As a result of reducing dietary crude protein content and supplementation with amino acids, the efficiency of dietary N utilisation for milk protein synthesis increased by between 14 and 18%, while N excretion was reduced by between 17 and 26%. As in the study of Kebreab et al. (2001), the main effect was that the proportion of urine N in the total N excretion declined from 63% (control) to 52% (supplement 2). ). Similar responses have been reported in other studies (Leonardi et al., 2003; Noftsger and St-Pierre, 2003) but these have tended to be short term studies involving mid-lactation cows, and their effectiveness with high yielding cows in commercial dairy herds over long periods is uncertain. If these results could be repeated consistently, the supplementation of low protein diets with rumen protected lysine offer the potential for improving dietary N utilisation and reducing N excretion. However, such benefits do not come without a cost. The present product cost:milk price ratio in the UK is currently such that it is difficult for farmers to justify the inclusion of protected amino acids in the diets of dairy cows.

Robert et al. (1989) have suggested that any marginal reduction in milk yield will be offset by the positive effect of amino acid balance on milk protein production. However, since most milk contracts in the UK do not include payment for protein, the use of synthetic amino acids would not confer any financial benefit in this respect. Moreover at low dietary crude protein contents more attention would need to be paid not only to lysine and methionine but other potentially limiting amino acids (Sloan, 1997).

It appears that caution also needs to be applied when supplementing diets with protected amino acids, since an oversupply of as little as 140 to 150% for lysine or methionine has been shown to have a negative effect on milk production by dairy cows (Robinson et al., 2000).

(e) Synchronising energy and protein supply to rumen micro-organisms

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Synchronisation of rumen available protein and energy is considered as one method to increase the efficiency of N-utilisation and to decrease N-excretion by ruminants. Sinclair et al. (1993) reported that the formulation of diets that are synchronous for energy and nitrogen release in the rumen have resulted in an increase in the efficiency of dietary N utilisation. Since then, many studies have been undertaken to examine the potential for enhancing rumen microbial protein synthesis. The concept is attractive, but the experimental results regarding synchronisation of energy and protein in the rumen have been inconsistent.

(f) Use of alternative forages – forage maize

Reference has been made to the potential improvement in NUE as a result of substituting grass silage with maize silage in dairy cow rations (page 34). Figure 8 illustrates the potential reduction in N excretion by the UK dairy herd as a result of increases of between 5 and 20% in the amount of maize silage used in dairy cow diets. As discussed previously, improvements in NUE vary and so NUE’s of between 0.30 and 0.36 are given (a baseline of 28%, typical of grass silage-based diets, has been adopted). This calculation assumes that all the extra maize silage produced from the additional area of forage maize is fed to dairy cows over a 180-day winter, and that maize silage represents 50% of the forage in the diet, thereby maximising the improvement in NUE. A 10% increase in the area of forage maize would provide sufficient maize silage to feed 123 000 dairy cows. Depending on the NUE achieved, the reduction in N excretion may be expected to be between 215 and 862 tonnes over a 180-day winter. The maximum reduction in N excretion in this scenario is 1 700 tonnes N per year, but to achieve this will require a 20 % increase in the forage maize area and a 30% increase in NUE. While the latter is technically feasible, it will require maize silage with a consistently high starch content, a feature that is largely influenced by the weather conditions during the growing period. This reduction in N excretion as a result of improving NUE contrasts with an estimated annual N excretion by dairy cows in the order of 168 000 tonnes, i.e. about a 1% reduction in N excreted by the UK dairy herd.

(g) Use of alternative forages – sugar grass

Recent studies at IGER have shown that when grass with a high-sugar content is fed to dairy cows, the utilisation of the grass proteins increases. In one study cows consuming high-sugar grasses excreted 7% less N than those on conventional grass (Moorby et al., 2001). In other studies with mid/late lactation animals improvements in NUE and reductions in N excretion of up to 24% have been observed. In a further study, zero-grazed dairy cows in early lactation receiving high–sugar grass containing 50g/kg more WSC than the control variety, excreted 52g less N/d (a 17% reduction) than the controls. If 20% of the 2002 dairy herd were grazed on pastures with similar elevations in WSC content compared with standard varieties, and assuming a 52 g/d reduction in excreted N, annual reductions in excretory N of 3,238 t could be expected. This is equivalent to a 2% reduction in current N excretion by the UK dairy herd. The results of studies with high sugar grass (receiving 65 kg N/ha) have been compared with those in which different levels of fertiliser N have been applied (Peyraud and Faverdin, 1997; Keady and Murphy, 1998; Keady et al., 1998; Moorby et al. 2001). The NUE on the high sugar grass was 38% (Moorby et al., 2001) which compared with 35% on pasture to which no fertiliser N had been applied (Keady and Murphy, 1998). On ryegrass pasture receiving similar levels of N (60 kg/ha), NUE was only 26% (Peyraud and Faverdin, 1997), and declines still further as more N is applied.

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In addition to the change in NUE, these studies together illustrate the effect of forage type and level of fertiliser N application on the pattern of excretion, with both the amount and proportion of N excreted in urine increasing with N fertiliser application (Figure 9). While the amount of N in faeces of cows receiving the sugar grass is higher than other treatments, urine N is similar to that where no fertiliser N has been applied. The use of ‘sugar grasses’ therefore provides the opportunity of both increasing NUE by lactating dairy cows and reducing the proportion of N excreted in urine.

(h) Adopting management strategies to increase NUE

A recent study in the USA used milk urea nitrogen data from commercial dairy farms to examine the effect of different feeding and management strategies on NUE (Jonker, Kohn and High, 2002). It concluded that the efficiency of N utilisation by dairy herds was highly variable from farm to farm, and that most of this variation could be explained by the level of N feeding relative to recommendations, i.e. the main differences were diet related. Twenty five percent of the variation in NUE could be explained by the variation in milk production per cow. Ironically, management strategies employed to improve the accuracy of N feeding (forage analysis, ration formulation) appeared to have little impact. Strategies to increase production per cow (including the use of the growth hormone bovine somatotrophin, 3 times a day milking and photoperiod manipulation) appeared to increase N utilisation efficiency the most.

In summary, the most effective strategy for improving NUE by lactating dairy cows is a reduction in N intake, either as a result of reducing the N contents of the concentrate or forages in the diet, or both. Either approach, however, is likely to result in reduced milk yields per cow. While these approaches may reduce feed and fertiliser costs, the costs associated with purchasing and maintaining the extra cows needed to achieve quota will more than offset any reduction in feed and fertiliser costs. Thus the use of high sugar grasses provide an opportunity of both improving NUE and reducing fertiliser costs.

(iii). Scenarios for improving the NUE of forage-fed sheep and beef cattle

Imbalances in readily available carbohydrate and protein in the rumen, and the high solubility of forage N, particularly when intensively fertilised, have been identified as the key factors leading to poor nitrogen utilisation efficiency (NUE) of fresh and conserved grass. Scenarios using high sugar grasses (HSG) or maize silage (maize silage) are explored, as these have been consistently reported to improve the efficiency of utilisation of dietary N in various cattle and sheep enterprises. Although the use of legumes with naturally protected proteins, such as Lotus spp. or sainfoin are highly attractive, uncertainties surrounding their establishment and persistence in the UK make it difficult at present to base scenarios on such crops. Use of red clover with high contents of the enzyme polyphenol oxidase (PPO) shows considerable promise and this crop grows and yields well in many parts of the UK, including marginal land. However, data regarding beneficial effects on NUE are at the moment equivocal, possibly due to lack of information on the PPO content of the experimental red clover, making it currently difficult to produce meaningful scenarios based on this crop.

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(a) Sheep finished on High Sugar grass (HSG)

This scenario is based on recent data from an upland sheep farm study where ewes and their lambs grazed either HSG or control (standard WSC accumulating variety, CG) swards. When averaged across the entire study (184 days), lambs raised on the HSG grew 14% more rapidly than their counterparts raised on the CG swards (Evans, unpublished). Such enhanced production of lambs grown on HSG vs. CG has been reported in a number of other studies (Lee et al, 1999; Lee et al, 2001a). The estimated NUE of lambs raised on the HSG was 11% greater than for those grazing CG (Appendix 10). When extrapolated to the entire UK flock of lambs under 1 year old, this would result in a reduction of 1,731 t N ‘lost’ from the lambs grazed on HSG relative to those on CG over the 184 period. However, if grown on to the same weight as the HSG-raised lambs (assuming that they maintained their average growth rate of 0.196 g/d), GC grown lambs would need a further 26 days to attain the same finished LW as those raised on HSG. This would result in a further 11,719 t N being ‘lost’ by the entire UK flock. Thus, raising and finishing the UK lamb flock on HSG as opposed to CG would result in an overall reduction in N loss of 13,450 tonnes; a reduction of some 14% (Appendix 10).

Ewe carrying capacity was ca. 15 % higher on HSG than CG during the growing season (Lee and Scollan, 1999). If the entire breeding flock were grazed on HSG, there would be a corresponding reduction in the area of grassland required for breeding ewes. This would be accompanied by a similar proportional decrease in N fertiliser use, and if applied at 50-150kg N/ha, this would equate to a reduction of between 3,574 and 10,721 t N per annum.

If HSG were adopted for the entire UK flock of breeding ewes and fattening lambs, then a total reduction in the environmental burden of N from reduced excreta emissions and fertiliser application could be as high as 24,171 t N per growing season.

If 10 % of the UK fat lamb flock were raised on HSG, the reduction in N burden could be 2,417 t N per grazing season, or a reduction of 12,085 t N if 50 % of the fat lambs were grazed on HSG compared to conventional varieties.

While 98% of the HSG–raised lambs achieved marketable carcass composition, only 68% of those fed CG finished, realising £38 per head with 32% sold as stores at £32 per animal. If extrapolated to the UK flock, this would equate to a margin of £31 million of the HSG lamb sales over those grazed on CG. In terms of margin per hectare, when considered alongside the additional carrying capacity of the HSG sward, the margin per hectare over a control variety was calculated to be £344. The 15% reduction in fertiliser N use when HSG swards were used would result in a saving (assuming a cost of £390/t N) of approximately £1.4- £4.2 million. The cost of re-seeding UK pasture land with HSG for the entire flock of ewes would be equivalent to £72.3 million which could theoretically pay for itself within 3 years after establishment.

(b) Beef finished on HSG

In a study with Charolais cross beef steers finished on either HSG ryegrass, a standard control variety of ryegrass (CG) or permanent pasture (PP), it was found that growth rates were similar for those grazing HSG or PP, but significantly lower for those grazing the CG (Davies et al., unpublished). The N contents of the CG and HSG were similar, but that of the PP was ca. 30% higher. The NUE of the HSG was 23 and 28% higher than those of the CG or PP swards respectively. The combination of reduced HSG sward N content compared to PP and enhanced growth rate of HSG–grown animals, relative to those raised on CG, resulted in overall reductions of N ‘loss’ of 21 and 24% for HSG animals compared to those grazing CG or PP respectively when grown to the same live weight. The increase in returns from use of HSG versus the CG variety has been calculated as £96/ha. When extended to the entire UK herd of finished beef cattle in 2002, reductions in N ‘loss’ through grazing HSG would be in the order of 18,200 and 22,150 t of N per finishing period, for CG and PP-fed animals respectively (Appendix 11).

If it is assumed that the NUE observed for the finishing cattle would also apply to beef cows and in-calf heifers, then the reductions in N ‘loss’ from the UK finishing beef and breeding herd during a 180 day grazing season from grazing HSG - as opposed to PP - would be in the order of 54,100 t N (Appendix 12).

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The supply of excess N over requirements from HSG would be approximately half of that from PP (Appendix 13). If the entire UK beef herd was to be grazed on HSG for 180 days per annum, then approximately 1.1 million ha. (approximately one-fifth of the British improved grassland area) would need to be re-sown with HSG, at a cost of approximately £155 million.

HSG can be grown in any area where ryegrass thrives, particularly the wetter west of the country. NUE by growing lambs and beef cattle grazing HSG has been shown to be enhanced by some 11 and >20% respectively compared to those grazing conventional swards. If HSG were grazed by the entire UK flock of breeding ewes and lambs (under 1 year old), together with the entire breeding and growing beef herd, the improved NUE would be reflected in reductions of N excretion of ca. 69,000 t N/year. This compares to conventional swards or 78,355 t N if the beef herd were grazed on permanent pastures of similar N content to those in the study. It may be unreasonable to assume total conversion of UK grassland to HS grass. However, if 10 or 50 % of the combined beef and sheep flock grazed HSG reductions could respectively equal 6,8785 or 34,400 t N per grazing season, compared with CG, or 7,836 or 39,177 t N compared with sheep grown on CG and beef on permanent pastures.

A >3.5 % point differential in WSC content between HSG and conventional grasses is required to elicit an improvement in NUE. HSG performs well agronomically, but the genetic potential of currently available HSG varieties to accumulate high levels of WSC is not always expressed due to strong environmental interactions (Halling et al., 2004). Therefore, under some circumstances HSG may have similar levels of WSC to the best control varieties; however the development of ever-higher HSG varieties (see page 18) may well eliminate this effect.

(c) Maize silage for beef cattle.

A number of studies have been undertaken that have demonstrated improved production and N utilisation by beef cattle when fed maize silage-based diets. Bryant and Beever, (2000) reported that compared to grass silage fed-beef cattle, those fed maize silage as the sole forage had 35% increased DLWG. As a result, they finished 44 days earlier than their grass silage-fed counterparts. They also required 15% less feed, despite being fed iso-nitrogenous diets, achieved by feeding 2 kg per day of concentrates differing in N content. The NUE of the maize silage fed cattle was 10.14% compared to 7.94 for those fed grass silage. It was suggested that the 28% improvement in NUE was due to a combination of increased DMI and better balance of energy and protein supply to the rumen from the high starch maize silage. This in turn resulted in more rapid growth and hence a lower proportion of N being required for maintenance. The authors concluded that use of maize silage resulted in substantial financial benefits, such that despite higher growing costs of maize silage, maize silage was some 11% less expensive in terms of energy supply. This, coupled with the improved animal performance, resulted in 13 and 20% reductions in the cost of live weight and carcass gains respectively.

The NUE of maize and grass silage mixes in the ratios of 33:67 and 67:33 by beef cattle were 9.2 and 9.8 respectively, some 16 and 24 % greater than that of those fed grass silage as the sole forage (Bryant and Beever, 200). Extrapolating these results, reductions of N loss for the entire UK finishing beef herd fed maize or grass and maize silage mixtures (ratios of maize to grass silage of 33:67, 67:33 or 100% maize silage) would be in the order of 6,500, 9,150 or 10,250 t N per finishing period, respectively, compared to those animals fed grass silage as the sole forage (Appendix 14). The NUE observed with the finishing beef is a conservative estimate of that of maize silage alone, due to the diluting effect of the concentrate portion of the diet. Nevertheless, if the improved NUE observed for the steers is assumed to hold good for the other categories of cattle in the beef herd (cows and in-calf heifers) then this would result in a reduction in N excretion from the entire herd of at least 18,000, 30,000 and 38,000 t/N if maize and grass silage were fed at 33:67, 67:33, or 100:0, respectively, compared to an all grass silage diet. These values represent reductions in N excretion of 11, 19 and 24 % compared with grass silage. In terms of oversupply of N, feeding maize and grass silage in 2:1 ratio would result in ca. 66% reduction in the excess supply of dietary N above animal requirements (Appendix 15).

Uptake of diets containing maize and grass silages in the ratio 67:33 by 10 and 50% of the entire beef herd would result in reduction of N ‘loss’ of 3,010 and 15,010 t/N respectively.

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From a financial perspective, a 12% reduction in costs per kg carcass gains through feeding maize silage: grass silage at 67:33 would equate to a saving of £133 million for the total home-fed production of beef in 2002. Although compared to feeding grass silage, feeding 100% maize silage plus 2kg concentrate was calculated to reduce the excess of dietary N by 87.5 %, it is unlikely that 100% maize silage would be fed in all forage-based systems, due to the necessity of supplementation with additional protein.

The land area in the UK on which forage maize will grow imposes constraints on the amount of maize silage available for beef production. If the whole beef herd was to convert to maize silage, at a ratio of 67:33 maize and grass silage, approximately 5.6 million tonnes (DM) would be required over the 180 d housed feeding period. This would necessitate a near 4-fold increase in the area of forage maize currently grown in the UK. The advent of extremely early varieties of forage maize, which thrive at a maize heat unit (MHU) index of 1200-1249, will allow the crop to be grown in much of lowland Britain. This compares to conventional, 2nd early varieties with an MHU index of 1300-1345, which are largely confined to the coastal regions of Southern England and Wales. Quadrupling of the forage maize is possibly achievable with extremely early varieties, but may not necessarily be desirable from an environmental or aesthetic perspective. Although the area under production might be expected to increase if predicted increases in temperatures are realised, elevated temperatures will favour higher maize yields only where there is sufficient soil moisture. Simulation studies have predicted that higher temperatures accompanied by 0.10 reduction in precipitation would result in a reduction in DM yields in the south and South-east of England (Cooper and McGechan, 1996; Davies et al, 1996). Since the value of the crop is insufficient to justify irrigation, expansion in the production of maize may be concentrated in the western and northern regions of the UK, which receive higher rainfall but are currently too cool for maize production.

(d) Fertiliser: improved management and reductions in application

‘Background’ levels of soil mineral N (nitrate and ammonium) are substantial. For example, they have been reported to be ca. 185kg/ha in Ireland (Ryan, 1976). This represents an important source of N for sward uptake, and addition of fertiliser should therefore be regarded as augmenting soil N to achieve a desired target. Monitoring soil mineral N throughout the growing season and adjusting fertiliser applications accordingly resulted in average reductions in fertiliser application and nitrate leaching by 28 and 40% respectively in on-farm trials (Brown and Scholefield, 1998). Such an approach can be further refined by use of computer models that determine plant N requirements for any given site and conditions to meet set targets, which may be production or N-loss-based. Integrating information on soil N status with using these models provides information on the timing and levels of fertiliser to be applied at a given site to achieve the desired crop response with minimum environmental impact (Brown and Scholefield, 1998). Use of such methods is invaluable to farmers in nitrate vulnerable zones, and has the potential to reduce the all-too-common practise of applying ‘insurance’ amounts of N fertiliser.

The Nitrate Directive requires that measures be implemented to control agricultural practises, if the maximum acceptable concentration (MAC) of 50mg nitrate/l. of water is exceeded. In Britain, the Directive has been applied by dividing the country into nitrate vulnerable (NVZ) and non-vulnerable zones. In NVZ, the Nitrate Directive restricts the timing and rate of fertiliser and manure applications, with whole-farm organic-N loading (animal excreta) being limited to 210kg/ha for the first four years and 170kg/ha thereafter should there be no improvement in water nitrate status. These restrictions are calculated to equate to stocking rates of dairy cows yielding 6000 l/annum of 2.2 (210 kg/ha) or 1.8 (170 kg/ha) animals/ha/year. Corresponding values for beef cows are 3.5 or 2.8 (extrapolated from data in Humphreys et al., 2002; NAEI, 1997). Such stocking densities will clearly reduce the need for synthetic fertiliser in many cases. Indeed, when stocking densities were reduced from 2.5 to 2.1 LSU/ha, whole farm NUE was increased from 21% to 30%, largely due to a halving in the amount of N fertiliser used (Humphreys et al., 2002). In a survey of farms in New Zealand, where N fertiliser application averaged 40kg/ha, whole farm NUE was 30%, compared to 16% for farms in the SW of England where fertiliser application was 250kg/ha (Ledgard et al., 1997). Thus, NVZ legislation on its own has the potential to substantially improve whole-farm NUE, and by definition N utilisation by ruminant livestock. A number of other EU states have applied the NVZ restrictions countrywide, an approach, which, if

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adopted in the UK, could significantly reduce N losses throughout the British farming industry. Indeed, if all dairy farms adopted a maximum stocking density of 2.2 cows, the vast majority of their annual DM requirement may be met from ryegrass swards fertilised with 160 kg N/ha, some 20-30 kg less than the average amount currently applied to dairy pastures (Rush et al, 2001). Additional benefits of reducing the level of N fertiliser inputs are the decrease of herbage N and increase in WSC that would ensue.

(e) Discussions

It is clear that balancing the supply of NSC:N to the rumen and reducing oversupply of N are key factors in improving NUE by ruminant livestock and whole farm NUE can be substantially enhanced through use of tactical fertiliser application. These key issues can be addressed by:

Provision of fresh and conserved forage with inherently high contents of NSC and comparatively low N contents e.g. HSG or maize silage,

Raising the protein content of high NSC maize silage up to, but not above, the protein requirements of the animal by appropriate mixing with legume or grass silage

Reducing stocking densities, allowing reduced fertiliser application, resulting in raised NSC, reduced NPN, with consequent increases in NUE

Targeted application of fertiliser to match supply with sward requirements, through soil monitoring and use of computer models.

Use of forage legumes such as red clover with protected protein both for grazing and ensilage will undoubtedly become important when more research data becomes available.

Use of forage legumes with protected protein, both for grazing and ensilage, will undoubtedly become important in strategies to improve NUE. Their justification would be enhanced when (a) more research data becomes available for crops such as red clover with known PPO levels, and (b) more consistently yielding and persistent varieties of high-tannin crops such as sainfoin or Lotus sp. are developed or identified.

(iv): Impact on N emissions

The effect of some of the scenarios described above on ammonia emissions and nitrate leaching are given below.

Ammonia

Table 17. Impacts of scenarios described above on national ammonia emissions.

Livestock Scenario NH3-N reduction,t x 103

% reduction of UK NH3

emissions from agriculturePigs EAA 8.293 3.3

Wheat based 1.469 0.6maize based 2.677 1.1Normal grain 7.313 2.9Low N Grain 9.109 3.7

Broilers Low N Grain 1.495 0.6

Sheep High-sugar grass 0.359 0.2

Beef steers High-sugar grass 4.549 2.5

Beef herd 100% grass silage (GS) - -67% GS, 33% MS 6.467 2.933% GS, 67% MS 11.170 5.1100% MS 14.109 6.4

Adoption of the proposed diets for pigs and poultry was predicted to reduce NH 3 emissions by between c. 1.5 and 9 t x 103 NH3-N. This is equivalent to reductions of between 0.6 and 3.7% of

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total agricultural NH3 emissions in 2000. However, it should be borne in mind that pig production accounts for only c. 10% of total NH3 emission from agriculture. Hence, while the reductions reported above appear modest, the best options for pig production represent a substantial reduction of the baseline emission from the pig sector.

For ruminants, the small reduction arising from this measure for sheep reflects the relatively small emission that arises from grazing. If it were assumed that the NUE observed for the finishing cattle would also apply to beef cows and in-calf heifers, then the reductions in emissions of 9.897 t x 10 3

NH3-N could be achieved. The adoption of a greater proportion of maize silage in the diet in place of grass silage has the potential to reduce NH3 emissions by up to c. 6%, depending on the proportion of maize silage currently in use. However, in view of the comments below, (see table 20) about the feasibility of sufficient land being suitable for conversion from grass to forage maize, the larger reductions reported above may not be achieved in practice.

Nitrate

Table 18. Impacts of scenarios described above on estimates of nitrate leaching.

Livestock Scenario Reduction in nitrate leaching, t x 103

Reduction in nitrate leaching (%)

Pigs EAA 0.773 0.19Wheat based 0.137 0.03maize based 0.250 0.06Normal grain 0.682 0.17Low N Grain 0.849 0.21





These diets were estimated to reduce the amount of nitrate-N (NO3-N) following manure spreading by between c. 0.1 and 0.9 t x 103 NO3-N, < 1% of the national total. This small impact is to be expected as losses following the spreading of manure account for only c. 5% of total NO3-N leaching. Much bigger reductions would be expected from reducing N excretion from cattle, not only because cattle produce c. 70% of N excreted by livestock, but also because they typically spend half the year grazing, and NO3-N leaching from grazed pastures is a bigger proportion of the total NO3-N leached. Hence the large-scale replacement of grass silage by maize silage in beef production may reduce leaching by c. 3-4%. This may also seem a disappointing reduction but, in this study, it was only possible to make estimates of changes to NO3-N leaching from the application of manures or deposition of excreta to land in the year of application. Over time the reduction of application of N to land will lead to reductions in the amount of N cycling within soil and hence to further reductions in NO3-N leaching.

Nitrous oxide

Table 19. Impacts of scenarios described above on estimates of nitrous oxide emissions.

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Livestock Scenario Reduction in nitrous oxide, t x 103

Reduction in nitrous oxide (%)

Pigs EAA 0.540 0.39Wheat based 0.692 0.50maize based 0.665 0.49Normal grain 0.162 0.12Low N Grain 0.522 0.38





Again, impacts on emissions of N2O are small. Bigger impacts are reported from cattle due both to the greater amounts of N excreted and the greater emissions of N2O from grazed pastures.

(b) Dairy cows

Ammonia

The scenario developed above (page 43) considered an increase in the maize acreage from 0 to 15%. Hence the number of dairy cows that could have their diets amended with this extra maize could only be c. 2-7% of the national herd (Table 20). The incorporation of more maize into the diet to would be expected to increase NUE from the current 28% (for grass silage) to between 30 and 36%. Several scenarios were therefore investigated of different combinations of the increase in area of maize and consequent increases in NUE from the greater use of maize in the diets.

Table 20. Dairy cows – impacts of changes in dietary-N intake on ammonia emissions

% increase in maize area

Number of cows fed with extra maize

% of national herd

Nitrogen Use Efficiency

% change in winter N excretion

decrease in NH3-N

emissions(t x 103)

5 51,944 2.22 0.30 0.972 0.035 51,944 2.22 0.32 0.944 0.065 51,944 2.22 0.36 0.889 0.1210 103,889 4.45 0.30 0.972 0.0610 103,889 4.45 0.32 0.944 0.1210 103,889 4.45 0.36 0.889 0.2415 155,833 6.67 0.30 0.972 0.0915 155,833 6.67 0.32 0.944 0.1815 155,833 6.67 0.36 0.889 0.36

At NUE of 30%, the use of additional maize in the diet is only expected to reduce N excretion during the winter housing period by c. 3%. It should be noted that winter N excretion is no more than 40-50% of annual N excretion by dairy cows housed for around 6 months of the year. In consequence of this small reduction in N excretion, and the potential applicability to only a small proportion of the UK dairy herd, if NUE increases to only 30% the measure will have only a negligible impact on national NH3 emissions, ≤0.1 t x 103 NH3-N. This represents no more than 0.05% of national NH3 emissions. Should the use of additional maize lead to an increase of 36%, then NH3 emissions may be reduced by approximately 0.4 t x 103 NH3-N, or about 0.14% of national NH3 emissions. The major limitation to this approach is the likely amount of maize that can be grown to feed a small proportion of the UK dairy herd.

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Impacts on nitrate leaching and nitrous oxide emissions

For the reasons outlined above, any reductions in nitrate leaching and nitrous oxide emissions from reductions in N excretion by dairy cows due to the increased maize acreage of up to 15% are likely to be nugatory.

(v): Summary and conclusions

There is potentially scope for improving NUE by both ruminant and non-ruminant livestock, by more closely matching the amino acid (in the case of pigs and poultry) or N (for cattle and sheep) requirements. For non-ruminants, considerable reductions in N excretion have been achieved in the recent years. These have arisen from better definitions of requirements and changes in feed selection and livestock management. For the future, the use of synthetic amino acids to more closely match requirements is likely to provide the greatest potential for improving NUE and reducing N excretion. However, there are costs associated with this, and given the current financial state of these industries there is unlikely to be a marked increase in their use while soyabean protein meal prices remain relatively low. Steps aimed at increasing the confidence of farmers and feed formulators in both the amino acid content of feeds and requirements of livestock would also be likely result in diets that more closely matched requirements and improvements in NUE.

For ruminants, improvements in NUE are most likely to result from more closely matching the N and energy supply to the rumen micro-organisms. The use of maize silage or high sugar grasses has been shown to do this, but the future expansion of areas sown to these crops is unclear. However, even a substantial increase in the size of the forage maize crop is only likely to have a small impact on ammonia emissions.

Section 3 (page 9) described possible changes in livestock numbers in response to external factors, including market demand and financial support. It was suggested that there would be reductions in the numbers of suckler cows and finishing beef (-12%), breeding ewes (-4%) and dairy cows (-9%) as a result of changes in CAP. Based on recent trends, pig numbers were also expected to decline, while poultry numbers are expected to increase. The effects of these changes on the environmental impact of livestock are difficult to quantify. As discussed elsewhere in this report NUE increases as productivity increases. Therefore, a reduction in N excretion as a result of a decline in beef and sheep numbers may be offset, at least in part, if a greater proportion of beef and sheep are reared on extensive production systems. Milk, on the other hand, is likely to be produced by fewer cows on more intensive systems of production. Whether this results in more efficient use of N (or P) is not clear, since efficiency is only increased if the longevity of cows is not reduced. A reduction in the number of lactations per cow will necessitate an increase in the number of replacement stock required, and result in an overall reduction in NUE at a farm level. For all livestock, estimates of the effect of changes in numbers on environmental impact are confounded by the extent to which the strategies described above are adopted. In the absence of reliable intelligence on current use of these strategies, estimating the possible effects of further uptake of these strategies is not possible.

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Section 9: Phosphorus

Phosphorus is an essential element. It is located in every cell of the body and has more known functions than any other mineral element in the animal body. It is required for processes including bone formation and maintenance, lean tissue growth, energy metabolism, fatty acid transport, phospholipid synthesis, amino acid metabolism, and protein synthesis. It is a component of nucleic acids, and as such is involved in cellular metabolism, enzyme systems, and buffer systems. It is also an important constituent of milk, and is therefore required in large amounts by a high yielding dairy cow.

Although the mechanism for digestion of phosphorus varies substantially between pigs and poultry, excess phosphorus to that needed for optimum production and growth is deposited in the skeleton where it benefits skeletal integrity. When animals are exposed to short term P deficiency they are able to reabsorb it. Phosphorus not required for metabolism, product or bone storage is excreted. In ruminants, regulation of P metabolism is complex, and involves regulation of absorption from the gut, mobilisation from bone, and secretion in saliva. Phosphorus is absorbed in the small intestine as phosphate, and P in the bloodstream is either retained in meat, milk, or bone, or secreted through saliva back to the digestive tract. Ruminants secrete large quantities of P in saliva, and this is a key component of P regulation. Absorbed P not used for growth, deposited in bone, or secreted in milk is returned to the rumen in the saliva and then excreted in the faeces.

Society is becoming increasingly concerned about the environmental impact of nutrients in livestock manure. Excretion of P in manure is of interest because of its effects when applied to land in excess of crop requirements, on water quality. Livestock utilise P inefficiently, excreting 60-80% of that consumed. Therefore, the majority of P brought on to the farm in feed stays on the farm (Knowlton et al., 2004). This Section examines the sources of dietary P, requirements by livestock for P, and strategies that are being and may be adopted to bring supply and requirements more into line.

Dietary sources of phosphorus

Cereals contain relatively uniform P concentrations (2.7-4.3 g P/kg DM), and vegetable protein sources even more (5-12 g P/kg DM). In contrast, the P concentration of forages varies widely, and is primarily influenced by the phosphorus status of the soil, the stage of maturity of the plant and the climate. Average P content of fresh grass in the UK is c. 3 g/kg DM, although values between 1.7 and 6.6 g P/kg DM have been reported (MAFF, 1990). Forage maize generally has a lower average P content (2.6 g/kg DM) but a similar range. Estimates of P supply from concentrates and forages are given in Appendix tables 3, 8 and 9.

In addition to P in vegetable feeds, additional supplementation – where it is necessary - is usually provided in the form of inorganic phosphate. Most phosphates used for feed are derived from natural rock phosphates, principally found in Africa, northern Europe, Asia, the Middle East and the USA. In their natural form they are unsuitable for direct use in animal feed, but following chemical treatment the phosphorus they contain is changed into the orthophosphate form, which is highly digestible.

Livestock P excretion and the environment

Phosphorus not required for metabolism, growth, production or storage is excreted. Phosphorus losses in runoff from farmland are an environmental concern mainly because the P promotes algal growth in watercourses following eutrophication. Relatively small amounts of P (c. 2 kg P/ha; Haygarth et al., 1998) are lost to water from land under intensive dairy production under ‘average’ conditions, causing high environmental impact at the catchment level through eutrophication of rivers, estuaries and lakes. Defra is committed to taking action on diffuse water pollution (including P) to meet a number of national, European and international commitments on water quality, and legislation to regulate P concentrations for good water quality is expected under the Water Framework Directive (2000/60/EC). It is generally accepted that P from livestock manure applied to land is one of the major sources contributing to soil P accumulation, and that P excretion in manure largely depends on the level of P intake (Ternmouth, 1989; Metcalf et al, 1996; Khorasani

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et al., 1997). In the UK, approximately 90 million tonnes of livestock manure containing c. 120,000 tonnes of P are recycled to land each year. Agriculture contributes about 43% of P inputs to surface waters in the UK, of which ~30% comes from livestock manures. Therefore, accurate and precise management of phosphorus nutrition is crucial to optimise performance and health of dairy animals, while minimising any adverse environmental impact arising out of P excretion.

Meeting the phosphorus needs of livestock

In order to meet the P requirements of livestock in the most sustainable and cost effective manner, it is necessary to know both the requirements for P of the livestock concerned, and the bioavailability of the P.

Requirements for Phosphorus

Requirements by different livestock for P have been published by a number of national authorities, including AFRC in the UK, NRC in the USA, INRA in France. In addition, many of the breeding companies publish requirements for specific strains of livestock. However, estimates of requirements vary between authorities.

For pigs and poultry, a factorial approach is taken to calculate P requirements of pigs. This method is based on the measurement of the retention of P in the body, foetus or milk, its obligatory losses and its digestibility. Requirement for growth corresponds to body P retention. However, many approximations are still made, particularly for breeding sows, since the way in which P stores (in bones) are managed through lactation and gestation is still almost unknown. This lack of accuracy probably results in higher P recommendation in sow diets than are necessary and excessive P excretion via urine (Poulsen et al., 1999).

For poultry, the NRC (1994) has established a non-phytate P requirement of 4.5 g/kg for broilers from 0 to 21 d, declining to 3.5 g/kg from 21 to 42 d and to 3.0 g/kg from 42 to 56 d of age. However, companies supplying poultry recommend up to 5.0 g/g available P for starter feeds (0 to 21 d), 4.5 g/kg for grower feeds (22-37 d) and 4.2 g/kg from 38 days to market (Ross, 2000; Arbor Acres, 2005). There is a tendency within the industry to match, where possible, genetic guidelines. As a result, there can be significant differences in the target levels of dietary P.

Similar variation exists in estimates of requirements for ruminants. Some of these differences are illustrated in Table 21 for dairy cows at three different milk yields.

Table 21. Recommended P intakes of P by dairy cows (calculated from AFRC, 1991 (UK), GfE 1993 (Germany), NRC 2001 (USA) and Valk and Beynen 2002 (The Netherlands)).

Milkkg/d

DMIkg/d

Recommended P supply (g/d)UK Germany USA The Netherlands

15 17 56 46 51 4025 20.3 77 65 65 5545 26.9 121 103 96 83

These differences are due mainly to different methods of calculating net maintenance requirements and absorption coefficients, but they clearly have implications for providing advice to farmers on the extent to which P intake may be reduced.

The bioavailability of dietary phosphorus

It is well known that phytic P, which is the main storage form of plant feedstuffs and accounts for 50 to 80% of P in these materials, is poorly available to monogastric animals. In contrast, it is well utilised by ruminants because of phytase enzymes produced by the rumen micro-organisms. Strategies for improving the availability of feed P are discussed below, but it is clearly necessary

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to know the extent to which the P in feedstuffs – either with or without processing – will be digested and contribute to meeting the animals requirements.

For many years nutritionists involved in non-ruminant nutrition have examined the relationship of various in vitro solubility tests of feed phosphates with their biological value (BV), as estimated by poultry chick studies. While relationships between BV and solubility in certain substances have been reported, no in vitro tests have been identified that are able to adequately estimate P bioavailability in animal feeds. Until one is developed, bioassays will remain the main method for evaluating bioavailability. However, these studies are both expensive and time consuming to do undertake. It is not surprising, therefore, that where uncertainty exists as to the bioavailability of P that farmers and feed formulators will err on the side of caution and provide more P than may be necessary.

Strategies for improving P utilisation by farm livestock

Strategies for improving the utilisation of dietary phosphorus (P) and reducing the phosphate content of manure of farm livestock have been the subject of many reviews (e.g. Tamminga, 1992; Jongbloed and Lenis, 1998; Lee, 1999; Withers et al., 1999; Hemke, 2002; Verstegen and Tamminga, 2002; Tamminga, 2003; Cerosaletti, Fox and Chase, 2004). Some of the strategies considered to offer the greatest scope for improving dietary P utilisation by pigs and poultry are described below. Because of differences between ruminants and non-ruminants in the digestion and metabolism of P, they are discussed below separately.

(i) Pigs and Poultry

Typically, between 50 and 80% of the P present in the main feeds for pigs and poultry (cereal grains, oil seed meal, and by-products that originate from seeds) is present as Phytate-P. This is the principal storage form of phosphorus in these feeds, but it is generally not available to non-ruminants because they lack the digestive enzyme, phytase, required to separate phosphorus from the phytate molecule23. Because pigs and poultry are unable to digest P in this form, it is excreted, increasing the amount of phosphorus in the manure. Several important consequences of the inability of pigs and poultry to utilise phytate-P may be noted. First, expense is incurred when inorganic phosphorus (e.g., dicalcium phosphate, defluorinated phosphate) or animal products (e.g., meat and bone meal, fishmeal) must be added to meet the pig's requirement for phosphorus. Second, phytate can bind to a number of minerals (calcium, zinc, iron, magnesium, copper) in the gastrointestinal tract, rendering them also unavailable. A number of strategies have been identified that may improve the utilisation of dietary P.

Feed processing

Lee (1999) reviewed the effects of feed processing on improving P availability in pigs. These principally involved either pelleting or soaking, and improvements were due to the presence of phytase activity naturally present in the feed. For both methods, improvements in digestibility were variable, due largely to the type of feed involved and the level of phytase activity present at the time of processing. Soaking feeds is a time consuming and labour intensive and only suited to small pig units. Commercial pig fed production usually involves pelleting, and consequently improvements in availability may be expected as a result of this process. However, due to the natural variation between feeds both in their P content and phytase activity, and the lack of a rapid method of measuring these, manufacturers are unlikely to modify diets or levels of P supplementation based on these criteria.

Selection of feeds with higher P availability

Traditionally, the P requirements of pigs and poultry have been met by supplementing with inorganic P, with the non-digested phytic-P and any excess supplementary P is excreted in the faeces. Because some feedstuffs are high in phytate, and because there is some endogenous phytase in certain small grains (wheat, rye, triticale and barley), there is wide variation in the bioavailability of P in feed ingredients. For example, the P in maize grain is only 12% available

23 Phytase enzymes have been isolated in small amounts from the small intestines of broilers and laying hens (Maenz and Classen, 1998).

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while the P in wheat is 50% available. The P in dehulled soybean meal is more available than the P in cottonseed meal (23 vs. 1%), but neither source of P is as highly available as the P in fishmeal (93%) or dicalcium phosphate (90-95%). Similarly, P availability in different forms of dicalcium phosphate can vary from 89 to 100% compared to monocalcium phosphate (Jongbloed et al., 2000). The choice of feed material and/or source of supplementary P can therefore have a significant impact on the amount of P absorbed or excreted by non-ruminant livestock. The variability in P availability between fed types is illustrated in Table 22.

Table 22. Digestibility of phosphorus of vegetable and animal origin24.

P content Phytate P Digestibility of total PPigs Poultry

g/kg % total P % %Barley 3.6 70 30 38Maize 2.9 70 20 30Wheat 3.4 65 26 38Rape seed meal 10.8 75 27 33Soya bean meal 6.5 70 39 42Tapioca 0.9 20 10 66Wheat middlings 10.9 85 20 27Maize gluten feed 8.8 70 20 40Meat meal 31.1 2.6 59 65Fish meal 23.8 2 72 74Bone meal 74.4 4.3 64 59Meat/bone meal 59.4 6 69 66

As illustrated above, a greater proportion of P is present as phytate-P in vegetable rather than in feeds of animal origin.

The use of feedstuffs with high intrinsic phytase activity in diets in order to release P from other feedstuffs has been proposed as a means of improving P utilisation (Pointillart, 1991). However, the variability of phytase activity encountered within feedstuffs is large (Eeckhout and De Paepe, 1994) and in the absence of rapid, reliable and cost-effective means of measuring phytase activity of feeds it is unlikely to be a reliable approach. Since the enzyme is susceptible to heating, this approach will only be effective where feeds are not exposed to high temperatures during manufacture.

A number of plant breeding programmes are in progress to breed plants containing low levels of phytate P. Mutations that reduce phytic acid levels throughout the plant have been isolated in maize, barley and rice, and varieties of maize (corn) with reduced phytate are currently available in N America. An alternative approach to over-coming the effects of phytic acid is through synthesis of phytase in the seeds of transgenic plants. Recently, genetic modification of soya beans has resulted in seeds with higher phytase contents, but it has not been able to withstand the processing temperatures necessary to inactivate the anti-nutritional factors present in soya beans.

Use of exogenous enzymes

Pressure to reduce phosphates in animal manure in Europe and the USA provided the impetus to develop exogenous phytase enzymes that allowed the animal to digest significantly more of the plant P, and thus reduce reliance on inorganic sources of supplementary P. Levels of P in pig and poultry diets - and manure - have been reduced significantly as a result of including phytase enzymes in pig and poultry diets. It has been calculated that the inclusion of exogenous enzymes in diets of growing/fattening pigs and sows has reduced annual P intake by 16% and 33%, respectively (De Boer et al., 1997). For poultry also, it has been suggested that P excretion can be reduced by up to 70%, and manure volume by up to 14%, as a result of using dietary phytase (Graham et al., 2003). Since the excess would have been excreted in manure, this represents the reduction in excreted P that might have been expected. Responses to the addition of microbial

24 Source: Centraal Veevoeder Bureau (CVB), The Netherlands

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phytase appear to be curvilinear, with the maximum P digestibility approximately 60-70%, even at high levels of phytase supplementation (Jongbloed and Lenis, 1998).

While phytate P itself is not readily available to pigs and poultry, there appears to be some variability in the digestibility of phytate P when phytase is added to the diet. This is mainly due to a wide variation in the phytase activity remaining in the plant material, which is influenced by feed type (Eeckhout and Paepe, 1994, Bedford, 2000) and factors such as method of feed processing. Responses to phytase are also known to be influenced by the age of the animals, dietary content of calcium, phosphorus and vitamin D in the ingredients used (Bedford, 2000). Thus, responses to phytase supplementation are not always predictable.

Four microbial phytases are currently authorised for use in the in European Union as additives in pig and poultry diets. Including phytase enzymes in the diets is usually cost-neutral. Industry sources suggest that phytase is incorporated into approximately 90% of pig diets, 90% of layer feeds and 40% of broiler rations (AIC, 2005) manufactured in the UK. The main reason for the lower levels of inclusion in certain diets is that the enzyme is not stable at temperatures used in some plants for the manufacture of compounds for growing/fattening pigs and sows. For these, the enzyme has to be added in solution, post-pelleting. New compound manufacturing plants are likely to include facilities for application of enzymes post-pelleting, which should facilitate the use of more enzyme. Based on current use of phytase in Great Britain, AIC (2005) have estimated that the current saving in dicalcium phosphate use is in the order of 19,400 tonnes per annum, which represents a saving of some 3,490 tonnes of P. The addition of phytase enzymes in 50% the remaining broiler diets that currently do not include it would provide a further saving of 10,240 tonnes of dicalcium phosphate, or 1,843 tonnes of P.

Diet supplementation with inorganic P

Although it is often assumed that inorganic feed phosphates have high phosphorus availability, research has indicated that there are significant differences in available phosphorus content between different types of phosphate, as well as between the same phosphates from different sources. Investigation of 20 commercial dicalcium phosphates demonstrated differences in availability, compared to a highly available phosphorus source, of as much as 30% (Waibel et al. 1984). These variations were explained by the different compositions and chemical structures of the phosphates tested. This information is clearly important in order to formulate diets for pigs and poultry, and reinforces the need for an effective means of estimating the P availability in livestock feeds.

Reducing dietary P concentrations

A straightforward reduction in dietary P concentration may be expected to improve P utilisation and reduce P excretion. Phosphorus requirements have been published by a number of national expert bodies. These are designed to take into account performance levels, age and genotype. These are usually expressed as digestible phosphorus in the case of pigs and available phosphorus in the case of poultry. Dietary allowances are normally calculated to meet the animal’s requirement, but with a safety margin added to take account of genetic differences between individuals in a herd or flock, fluctuations in feed intake and variability in feed composition. The safety margin is usually 5-10% of requirements, although this is not fixed and may exceed this where a producer believes this is necessary to maintain the health or productivity of his stock. In other words, diets may be over-formulated to provide a measure of security. While the importance of the safety margin should not be underestimated, there may be scope for some reduction in some flocks and herds.

Persuading producers to reduce dietary concentrations of phosphorus may therefore provide a means of increasing efficiency and reducing P excretion by pigs and poultry. However, this approach needs to be handled with caution. Legislation in The Netherlands in the 1990’s to reduce phosphorus waste resulted in a reduction in the total amount of dietary phosphorus permitted in compound feeds. However, field observations showed that reductions in phosphorus levels of the order of 20% - 25% had an adverse effect on the performance of broiler breeding stock during the rearing and production stages, as well as on broilers and commercial layers (van Tuijl, 1998). Among the effects were increased mortality, a greater number of leg problems,

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including bone breakage in layers, poorer egg quality in layers and breeders and reductions in uniformity in broilers and young broiler breeding stock. Increasing the dietary phosphorus levels by 10-15% on the farm, combined with improved management conditions and a reduction in disease pressure, resulted in animal performance returning to normal levels. This experience illustrates the necessity for any reduction in mineral levels in the feed, including phosphorus, to be closely monitored under field conditions.

With increasing age, the quantity of P required by growing pigs and poultry increases. However, due to increased levels of feed intake, the P concentration of the diet necessary to meet requirements decreases (NRC, 1998). The more frequently a diet is reformulated, the more accurately the nutrient needs of the animal will be met, and the increased efficiency of utilisation will result in a reduction in nutrient excretion. Phase feeding has therefore been proposed as a management tool for reducing nutrient excretion. Using estimates of the P requirements of pigs during the growing and finishing period, and published estimates of feed efficiency, Knowlton et al. (2004) calculated that the use of a three phase feeding system would result in a reduction of 12.5% in P excretion, relative to a single level set to meet the needs of the youngest pigs (0.5% P). However, phase feeding is widely practised both in the pig and poultry industries, and it is not clear what scope there is for further reductions P intake/excretion using this approach.

Livestock breeding

Research groups in the USA have developed transgenic pigs capable of synthesising phytase enzyme in the salivary gland (Golovan et al., 2001; Forsberg et al., 2003). The phytase excreted in the saliva of the transgenic pigs releases phytate P from animal feed, reducing the need for dietary phosphorus supplementation and reducing P excretion. True P digestibility using soybean meal as the sole source of P was approximately 50% in normal pigs and nearly 100% in the transgenic pigs. In addition, there was a 75% reduction in total phosphorus content of faecal matter between normal and transgenic phytase pigs (Golovan et al., 2001). Using computer simulation, Forsberg et al., (2003) estimated that 33% less land would be required to spread manure from transgenic phytase pigs, and if the diet were modified to decrease crude protein, even less land would be required. While transgenic technologies that improve nutrient efficiency are possible, many technical, ethical, and consumer acceptance issues remain to be resolved. The extent to which consumers of pig meat, livestock producers and the public in general, will accept this technology is not clear. Further research is needed both in the country of origin and in countries to which the product is to be exported to ensure that they do not have a deleterious effect on human health and/or the environment. Consumer surveys, in N America at least, suggest that transgenic technology directed towards issues involving environmental sustainability and food safety would receive greater support than has been shown to date for transgenic research.

In addition to developments described above, developments in breeding of genetic lines of pigs and poultry with higher growth rates and feed conversion efficiencies have resulted in improved P utilisation and reduced P excretion, compared to older, slower growing genetic lines. These reductions have come about primarily through reduced time to market age, and therefore reduced maintenance requirements.

(ii) Ruminants

In contrast to pigs and poultry, ruminants have a digestion system in which micro-organisms in the rumen produce enzymes capable of making the phytate P of plant material available to the host animal. Phosphorus from these sources is therefore better suited to ruminants, although as a general rule is still utilised by the animal to a lesser extent than the phosphorus provided from inorganic sources. The ruminant’s nutritional requirement is therefore dictated by both the needs of the animal and the needs of the microbial population in its rumen. The main source of P for rumen microbes is that which is recycled in saliva. If the P supply is insufficient, cellulose digestion by the rumen bacteria is affected, causing a decrease in the feed digestibility, reduced feed intake and lower production.

Phosphorus supplementation of ruminant diets is essential for profitable and sustainable livestock production. However, there is evidence that the levels of P in dairy cow diets is significantly higher than recent research would suggest necessary (Valk and Sebek, 1999; Wu and Satter, 2000).

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Reasons for this have recently been reviewed (Satter, 2002), but include concerns over the variation in P contents of feeds and uncertainties associated with P availability in mixed diets. Strategies for reducing P intake by ruminants need to address these concerns.

Assumptions on the availability of dietary P

In recent years there has been a trend towards using available P rather than total P in formulating diets for ruminants. This has had the effect of reducing the dietary P concentrations by about 0.1 percentage units (e.g. from 0.5% as recommended by AFRC (1991) to 0.4% (NRC, 2001) for a cow yielding 40 kg milk/day). As a result of this there has been significant reductions in the use of dicalcium phosphate in dairy cow diets. Prior to 2000, it was not uncommon for dairy compound feeds to be supplemented with dicalcium phosphate at a rate of 2.5 kg/tonne. Today, dicalcium phosphate supplementation in dairy compounds has virtually ceased, This, it is estimated, has resulted in a saving of about 5 650 tonnes of dicalcium phosphate, equivalent to 1 017 tonnes of P (AIC, 2005).

In ruminants, most of the phytase consumed is hydrolysed and generally only trace amounts appear in the faeces (Morse et al., 1992). For this reason, many nutritionists have assumed that the availability of organic P n the diet is a constant. Yet despite the high degree of phytase activity in the rumen, there appear to be considerable differences in apparent P availability from both forages and concentrates (Valk et al., 1999; Bravo et al., 2003). Phosphorus availability in concentrate feeds may vary from 0.33 (formaldehyde treated rapeseed meal) to 0.85 (wheat). Reasons for these differences are not clear, and warrant further examination. If confirmed, laboratory methods for assessing P availability in feeds for ruminants may be justified, as they are for non-ruminant livestock.

Other studies in Europe and the USA have also indicated that P availability may not be constant in ruminant diets, but may be affected both by feed type (Aguerre et al., 2002), and by level of feeding and stage of lactation (Kohn et al., 2002). Further research is required to determine the true availability of phosphorus in feed, particularly for high yielding dairy cows. In conjunction with this, a rapid and reliable method of determining the P availability of feeds is necessary.

Use of exogenous phytases

As described above, micro-organisms resident in the rumen of cattle and sheep secrete sufficient phytase enzymes such that phytic P is usually completely digested in the rumen. Therefore, there appears to be little scope for improving dietary P utilisation through using exogenous enzyme supplements added to ruminant diets.

Reducing levels of supplementary P

In dairy cows, dietary P is ‘excreted’ in milk, urine and faeces. Milk P concentration appears to be correlated to milk protein content, but is generally less than 1 g P/kg milk, while urine P concentrations are small even on high P diets (Wu et al, 2000). Therefore, faeces provide the main route for excretion for P that is not utilised, and as P intake increases, so the amount of P excreted in faeces increases (Wu et al., 2000; Satter, 2002, Dou et al., 2002; Chapuis-Lardy et al., 2004). This is illustrated in Figure 10 for a dairy cow yielding 45 kg milk/d and consuming 24 kg/d of DM with 66.7% digestibility (Wu et al., 2000). Increasing P intake is reflected in increasing P excretion. The range in P intake (60 -132 g/day) is equivalent to dietary P concentration of between 2.5 and 5.5 g/kg DM. The upper end of this range is typical of many diets for dairy cows being fed in the UK today. However, studies in Europe (Kirchgeßner,

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1993; Valk and Sebeck, 1999; Lopez et al., 2004) and N America (NRC 2001; Satter, 2002) suggest that dietary concentrations of 3.2-3.6 g P/kg DM are likely to meet the requirements of most lactating dairy cows, equivalent to ~80 g P/day. Based on the data in Figure 9, a reduction in dietary P concentration from 5.5 to 4.0 g/kg DM would result in a 38% reduction in P excretion.

Because there is no national survey of feeding practice in the UK, the extent to which high levels of P are fed in the UK are not known. However, a survey of ~600 dairy farmers in the United States revealed a wide range of dietary P concentrations for lactating cows, from 3.6 to 7.0 g/kg of feed DM. The mean was 4.4 g/kg, which was 34% above the level recommended by the NRC for 27.9 kg milk/d, the mean milk yield in the survey (Dou et al., 2003). Higher P concentrations in diets were not associated with higher milk yields; however, higher dietary P led to higher P excretion in faeces. On 84% of the farms surveyed, professional nutritionists rather than producers formulated the ration; as a result most producers were feeding more P than cows needed because the consultants recommended it. These authors concluded that ration formulation is a critical control point in reducing excess dietary P and P excretion. If P levels in the diets of dairy cows are to be reduced, it is the professional nutritionists and feed formulators, rather than dairy farmers, who need to be persuaded of the benefits of doing so, and to have confidence in data for dietary P supply.

As part of a recent Defra-funded study25, data were obtained on the milk produced and feed purchased on 46 dairy farm in England and Wales. This study showed that purchased feed P supplementation increased on average by 2.2 g/kg milk produced (Figure 11). This compares with a recommended rate of increase of 1.6 g/kg of milk produced by high yielding dairy cows (NRC 2001). Similar high levels of supplementation have also been reported from The Netherlands (Valk and Sebek, 1999).

The impact of reducing surplus P inputs in purchased feeds and fertilisers on milk and forage production was investigated in a comparison of three dairy farm systems on chalkland soils in southern England over a 3-year period (Withers et al, 1993). The ‘control’ treatment (system 1) represented production in accordance with current commercial practice, which accumulated an average annual surplus of 23 kg P/ha. Progressive reductions in purchased feed and/or fertiliser inputs into systems 2 and 3 decreased surplus P to 17 and 3 kg/ha, respectively, without apparently limiting either milk or herbage dry matter production. The estimated reduction in faecal P output from system 3 cows fed a low P diet compared to system 1 cows fed a high P diet was 26%. The results indicate there is scope to reduce surplus P on commercial dairy farms without sacrificing production targets, at least in the short term.

Since there is evidence that current levels of dietary P exceed requirements, why should dairy farmers feed P in excess of requirements, particularly when this has feed cost implications? The main reasons, reviewed by Satter (2002), appear to be:

a) Uncertainty over the total and available P content of feedsb) Uncertainty over requirements for productionc) Concern that lowering dietary P content will adversely affect dairy cow fertility.

a) Reference has been made (above) to the variability of P in ruminant diets. The development of a rapid and cost effective means of estimating P availability would allow producers to formulate diets that more closely matched requirements.

25 NT2402: Impact of nutrition and management on N and P excretion by dairy cows

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b) One of the reasons frequently given for recommending higher dietary P concentrations is the discrepancy between different authorities in estimates of requirements. Table 21 illustrates shows the amounts of P recommended in four different countries over a range of milk yields. The supply of P is calculated according to AFRC (1991), GfE (1993), NRC (2001) and Valk and Beynen (2002) for UK, Germany, the USA and The Netherlands, respectively.

For a high yielding dairy cow, there is a 40% difference in estimates of P requirements between the lowest (NL) and highest (UK) estimates. The main reason for the differences in P requirements is differences in estimating net maintenance requirement and absorption coefficients. When total P excretion is expressed per kg milk produced, it is clear that when milk yield increases, P in the manure decreases, reflecting the lower influence of maintenance P at high milk P outputs. In the UK and US systems, low producing dairy cows offered more P result in higher excretion per kg milk produced compared to the systems used in Germany and The Netherlands. More information is needed to define P requirement more precisely at low and high milk production levels. However, caution is required when recommending very low dietary P concentrations. Using the NL system and the DMI levels of NRC (2001), a cow producing 15 kg milk needs about 2.4 g P per kg DMI which level is likely to be too low for the rumen microbial need of P. At this level of feeding, it is possible that the rumen microbes need more P than the host.

Although there may be uncertainty as a result of the differences in ‘national’ standards, the NRC (2001) recommendations have been validated across a wide range of diets and production systems (Weiss and Wyatt, 2004), and would provide a sound basis for recommendations in the UK.

c) The third concern, namely that of possible adverse effects on fertility, may be more difficult to resolve. Although that the association between P intake and fertility was established on very low-P diets, many dairy farmers remain concerned that dairy cow fertility may be compromised if levels are reduced to those proposed by researchers. Largely because of the high cost of doing so, few long-term, multi-lactation studies have been undertaken to examine the effects of reduced P (to levels proposed by the research from the Netherlands and the USA) on fertility. However, there is no research data to show that cows benefit from feeding P in excess of requirements (Brodison et al., 1989; Brintrup et al, 1993; Wu et al, 2000). In a review of N American research studies, Wu and Satter (1999) showed that dietary P in excess of 3.2-4.0 g/kg DM had no effect on any of the fertility parameters examined when compared with 4.6-5.2 g P/kg DM. More recently, Lopez et al (2004) confirmed that a dietary concentration of 3.7 g/kg DM had no adverse effect on fertility. If UK dairy farmers are to be persuaded to reduce dietary P concentrations, data of this sort requires greater publicity, particularly to those responsible for formulating dairy cow diets.

One final reason why P is fed in excess of requirements is the inclusion of feeds in the diet that are naturally high in P. Many by-product feeds are high in P, most notably the cereal-based feeds (e.g. maize gluten feed, maize distillers’ grains, cereal by-prodycts). These are increasingly popular feed supplements for beef and dairy cattle because of the protein and energy they supply, and their cost relative to other feeds. However, inclusion of these feeds in higher amounts often increases the dietary P content beyond the animal’s requirement. The popularity of these high-P by-products is likely to continue, and there is no easy solution to the problem of the resulting elevated dietary P. In the short term, farmers using these feeds should at least remove unneeded supplemental inorganic P from diets, although currently little supplementary P is added to ruminant compound feeds26. Therefore to reduce the P content of current ruminant diets would require the selection of alternative feed materials, which would have cost implications. In the long run, the true cost of the use of these high-P feeds should be carefully considered. If the inclusion of these by-products will cause significant nutrient imbalance in the livestock operation and lead to difficulty meeting environmental regulations, then these feeds may not be as inexpensive as they appear.

Purchased feed has been identified as the single largest source of imported P on dairy farms (Cerosaletti et al., 2004; Laws et al, 2004). Consequently, dietary management should be taken as the first defence against P build-up on farms (Chapuis-Lardy et al., 2004). In the UK study

26 With the exception of calf compound feeds.

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referred to above27, feed P accounted for 65% of total P brought onto the farm. Similar levels have been reported in the Netherlands (Valk et al., 2000) and the USA (Klausner et al, 1998). In a recent study in the USA, a reduction in dietary P intakes on dairy farms, from 153% to 111% of estimated requirements (NRC, 2001) resulted in a 33% reduction in faecal P concentration and a 49% reduction in whole farm mass P balance (Cerosaletti et al., 2004). In the UK, reducing dietary P resulted in a 26% reduction in P excretion and in total farm P surplus (Withers et al., 1993). These studies confirm that dietary P management, particularly for dairy cows, can play a key role in reducing P imports on dairy farms, P excretion in manure and the build-up of P in soils (Kuipers et al., 1999; Valk et al., 2000; Powell et al., 2001).

Phosphorus losses in runoff following land application of manures have been linked to the solubility of P in manures (Suzanne et al., 1998; Sharpley. and Moyer, 2000; Kleinman et al., 2002). As a result of this, dietary effects on manure P solubility have also been examined. It appears that as P intake increases, the proportion of P that is soluble in water (PO 4), and therefore most susceptible to loss in the environment also increases (Dou et al., 2002; Chapuis-Lardy et al., 2004). Studies in the UK have also indicated that the nature of the forage in ruminant diets can influence the relative proportions of water soluble P in faeces (Shah, 1999). While the proportion of water soluble P in faeces of lactating dairy cows was < 25% on a grass silage based diet, there was a three-fold increase in water soluble P when whole crop cereal silage was included in the diet (at 60 % of the forage dry matter). Further studies are necessary to establish the reasons for these differences and confirm these effects under different dietary and management systems, but these results indicate some further potential for influencing both the total amount and form of P excreted by dairy cows.

The apparent over-supply of P is usually justified on the basis of uncertainty over the availability of P in mixed diets. Hemmingway (2000) has proposed that if consideration were to be given to reduce current levels of phosphorus used in practice, it would be essential for all feeds to be analysed in advance to determine available P concentrations. This is clearly not a practical option, since there is currently no rapid, non-invasive and reliable method for routine determination of the available P content of feeds. The P contained in fresh and conserved forage accounts for half or more of the total P intake of high-yielding cows, and both total and available P in forages is influenced by a number of factors including forage type and maturity, fertiliser application and the method of conservation. Failure to account for this variation could result in serious under-provision of P, which could be detrimental to health, production and reproduction. An alternative approach would be to develop a rapid, reliable and non-invasive in vivo test of nutritional adequacy. This is discussed in more detail below.

Conclusions

For non-ruminant livestock, the use of exogenous enzymes is likely to offer the greatest scope for matching dietary P content with requirements, thereby reducing P excretion. Development of crops with low phytate-P contents assist in reducing dietary P concentrations, but the use of transgenic pigs and poultry capable of secreting phytase enzymes is unlikely to be acceptable to consumers of pig and poultry meat and eggs, at least in the short to medium term.

The most effective means of increasing P utilisation and reducing P excretion by ruminants is to reduce the P content of their diets. There is evidence that diets for dairy cows in the USA and The Netherlands exceed apparent requirements, and anecdotal evidence would suggest this is the case in the UK also. Currently, however, the high levels of P are the result of the choice of feed ingredients, rather than the use of supplementary P, and to reduce dietary P levels would have cost implications for producers.

If lower dietary P contents are to be achieved, farmers, veterinarians and nutritionists need to be persuaded of the need for, and feasibility of doing so. Any adverse effects of P deficiency may not be seen for some years, and so a long-term programme should be established to monitor fertility and production of dairy cows on lower P diets (Hemmingway, 2000). The development of a simple indicator of nutritional adequacy (such as the faecal-P indicator) would provide farmers with greater confidence to reduce dietary P levels.

27 NT2402: Impact of nutrition and management on N and P excretion by dairy cows

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Despite small differences between authorities, dietary concentrations recommended by NRC (2001) would appear to provide a sound basis for P supply. In practice, dietary P levels as low as those recommended for The Netherlands (Valk and Benyon, 2002) may be hard to achieve, due to the relative high P concentration in forage crops and cereal by-products. Therefore, any increase dietary P utilisation by reducing diet P content needs to be accompanied by a strategy to reduce the amount of inorganic phosphate fertilisers on grasslands. Finally, because runoff is related to the water-soluble faecal P fraction, more information is needed about the relationships between level of P intake and feed composition on one hand, and faecal P fractions on the other.

The livestock feed industry in the UK has made considerable progress in reducing the amount of P added to compound feeds and livestock rations in recent years. The amount of P fed to livestock in the form of compound feeds and blends declined from 96,320 tonnes in 1999 to 76,728 tonnes in 2005, a reduction of 19,591 tonnes. Part of this reduction was a consequence of reduced livestock numbers and concentrate feeds sold, but AIC28 have estimated that adopting the nutritional strategies outlined in this report accounted for a reduction in P use of 10,099 tonnes.

Nevertheless, there are potential further reductions that can be made. In identifying strategies for improving P utilisation and reducing P excretion it is necessary to recognise that there are cost implications, which must be considered in a global food market. For example the inclusion of feed materials that have lower phosphorus content can significantly increase ration prices. Conversely there are reductions in phosphorus inputs that could be adopted both in the broiler industry and on dairy farms, which would have a positive impact on the environment and overall profitability when appropriately adopted. These situations should form the focus of the further reduction in phosphorus inputs to livestock units.

28 Impact of Improved Nutrition upon Nitrogen and Phosphorus supply to livestock from 1999 to 2005. Report from the Agricultural Industries Confederation (AIC)

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Section 10: Indicators of nutritional adequacy

Many producers supply N and P well in excess of the dietary requirements, but as indicated in this report they frequently do so because of uncertainty of supply in order to ensure sufficient intake. In effect, this is an insurance policy, and given the costs associated with under-provision it is one that most are prepared to pay for. These are, however, expensive nutrients and livestock farmers might be persuaded to reduce levels of N and P supplementation if sensitive and reliable indicators of nutritional adequacy were available. Two such indicators have been proposed.

Urea is a by-product of protein degradation and digestion and, because it diffuses readily into body tissue it is present in milk. A number of studies have shown that dietary N – or more specifically rumen degradable N - fed in excess of requirements results in elevated levels of milk urea N (MUN) (Jonker et al., 1998, Kauffman and St-Pierre, 2001; de Boer et al, 2002; Monteny et al., 2002). Moreover, there appears to be a direct and quantifiable relationship between the level of MUN and urinary N excretion (Kauffman and St-Pierre, 2001; Nousiainen et al., 2004). For example, in the study of Kauffman and St-Pierre (2001) the following equation is proposed to predict urinary N (UN) excretion based on MUN concentration and liveweight: UN (g/d) = 0.0259 liveweight (kg) x MUN (mg/dl).

It has been proposed, therefore, that MUN may be used to identify those farms where dietary N utilisation is low, and where changes in the amount or form of dietary N and energy supply may be an effective means of remedying these conditions. In the USA, the National Dairy Herd Improvement Association (DHIA) now offers MUN analysis along with the more familiar measurements of milk, and the information is used by farmers and their advisors to formulate diets in order to maximise dietary N utilisation. Data on milk urea content is also available to most UK dairy farmers. However, because diets fed to dairy cows in Europe differ significantly from those in North America, clarification of the relationship between diet and MUN concentration under European conditions is necessary.

The uncertainty that surrounds the estimates of requirements and the availability of P in feeds has been used to justify higher dietary P concentrations. One way of addressing these concerns would be to develop a test of nutritional adequacy, which would provide a farmer with reassurance that the P requirements of cows were being met. Water-soluble P in faeces has been shown to be highly correlated to total P in faeces and to P intake (Powell et al., 2001), and this has led researchers in the USA to propose the concept of a ‘faecal P indicator’ of P adequacy (Dou et al., 2002). Based on data from a number of feeding studies, they have identified a quantitative relationship between readily soluble P concentration in faeces and dietary P concentration. Using this relationship, these authors propose an empirical P benchmark, expressed as readily soluble P in faeces, of 1.73 to 2.00 g/kg faecal DM for diets containing 3.3 to 3.5 g P/kg DM. For each increment in dietary P concentration of 0.5 g/kg DM, they predict that readily soluble P in faeces would be expected to increase by 0.69 g/kg DM. This relationship has been derived from a limited number of studies carried out in North America, and clearly needs to be tested more rigorously if it is to be recommended for use in the UK conditions, particularly with forages used here. However, the development of a ‘Faecal P Indicator’ would have a number of advantages over simply relying on feed analysis and ration formulation to reduce P intake and excretion by dairy cows. In particular, it has the potential for diagnosing situations in which P is being unnecessarily added to dairy cow diets. Reducing dietary P levels in a way that does not compromise the health, production or reproduction of dairy cows would reduce feed costs for dairy farmers, help conserve P minerals from non-renewable resources and reduce potential environmental losses.

Also in ruminants, the amount of P excreted in faeces is closely related to the amount of P consumed. Moreover, water-soluble P in faeces has been shown to be highly correlated to total P in faeces and to P intake (Powell et al., 2001), and this has led researchers in the USA to propose the concept of a ‘faecal P indicator’ of P adequacy. This is based on measurements of soluble P in faeces (Dou et al., 2002), and a benchmark of approximately 2 g P/kg faecal DM has been proposed. Researchers in N America have suggested that this approach provides a simple management tool with which farmers are able to assess the adequacy of P intake of dairy cows. However, this requires further refinement, particularly to relation to livestock diets in the UK.

No similar non-invasive measures are available for non-ruminants.

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Section 11: Discussion and Conclusions

Considerable variation exists within the literature for N and P retention in useful food products. Much of the variation can be attributable to feeding of different ingredients, ages, or health status. In broilers, for example, N and P retention each had a range of 30 percentage units (Table 23).

Table 23. A summary of peer-reviewed publications (1985-2003) summarised for nitrogen (N) and phosphorus (P) retention by poultry (from Applegate et al., 2003)

Species Average % N retention Minimum Maximum Number of reports Broiler 60.2 44.0 73.5 11 Turkey 56.8 47.8 75 8 Duck 65.7 54.6 78.1 4 Laying hen 45.6 30 75.0 5

Average % P retentionBroiler, < 32 days 49.3 34 64.1 22 Broiler, > 32 days 41.0 36 51.0 5 Turkey 48.0 33.9 56 9 Duck 46.4 - - - - - - 1 Laying hen 29.1 13.6 44 20

Similar inefficiencies have been reported for pigs and for ruminants, and it is clear that there is scope for further improvements in N and P utilisation by all categories of livestock.

Nitrogen

Livestock, and particularly non-ruminant livestock, receive a significant proportion of heir feed N in compound feeds and concentrates. In the period 1999 to 2005 the amount of N provided in compound feeds declined from 400,523 to 344,976 tonnes. It has been estimated that 22% of this reduction in N use is the result of adopting some of the strategies described inn this report 29, while the remainder may be attributed to reductions in livestock numbers. Further numbers in livestock numbers described in Section 3 may be expected to result in further reductions in N input in livestock feeds.

Two general strategies have been proposed to improve N utilisation and reduce N excretion. The first is to improve animal productivity. As more milk, meat, or eggs are produced per animal, the maintenance requirement of protein per unit of production is reduced. Thus, the animal product can be produced with less N consumed and excreted. For example, present commercial poultry strains are more efficient in utilising nutrients and the present commercial feeds are better formulated to meet the requirements of the rapidly growing bird. Thus N and P excretion per kg live weight was 55 and 69% less, respectively from a 1991 commercial broiler strain versus a 1957 commercial broiler strain when fed the same diet (Havenstein et al., 1994).

The other way to improve utilisation is to improve the match between the quality of protein fed and that required by the animal. This will result in both lower dietary N contents and N excretion. Although improved productivity can increase N use efficiency, greater improvements are generally obtained through strategies that improve utilisation of dietary N, and these have been the focus of this study.

The N consumed by livestock is derived from a wide variety of feed materials. While it has not been possible to apportion amounts of feed (or N) consumed to the individual classes of livestock with any great accuracy, it is estimated that the total N consumed by the main farm livestock species is in the order of 1.62 million tonnes per annum. Almost two thirds of this is obtained from forages, either fresh or conserved, which are consumed almost entirely by ruminant livestock.

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However, there are real problems in estimating the amount of N consumed by livestock – in particular forage N intake by ruminants (page 13) – and it may be reasonable to assume that total N intake is greater than this.

Based on the number of livestock in Great Britain and using current estimates of requirements, total N requirements are in the order of 1.33 million tonnes. If all livestock diets were formulated according to these requirements, there would be a potential reduction of at least 290 kt N excreted by farm livestock. In fact the reduction is likely to be greater than this, since intakes of N intake are likely to be underestimated.

Conservation of N in animal production must begin by improving the N use efficiency of the animals. On dairy farms today, 20 to 30% of the N consumed by the herd is in the protein of the milk and meat produced (Dou et al., 1996). Pasture-fed dairy animals are at the lower end of this range, and pasture-produced beef may have an N use efficiency of less than 10% (Hutchings et al., 1996). In poultry or pig production, where the protein needs of the animals can be more closely met, this efficiency may average 30 to 35% and even approach 40% (Lee et al, 1998; Lenis and Jongbloed, 1999). While some of the remainder is retained in body tissue not consumed as food30, most is excreted in faeces and urine. By using the various management techniques described in this report, these utilisation efficiencies can be increased. It is worth noting, however, that although the maximum possible efficiency varies with animal species, age, stage of lactation, and so on, the theoretical limit is about 50% (Rotz, 2004).

This review has indicated that feeding strategies can be modified relatively easily, with quite dramatic effects. In the USA, the use on MUN data on dairy farms has allowed farmers to more accurately match protein supply with requirements, resulting in more efficient use of dietary protein and reductions in N excretion. In pigs and broilers, closer matching of amino acid supply to requirements by phase feeding or the use of synthetic amino acids has been shown to improve N utilisation. In practice, many integrated broiler producers and larger pig rearing companies already practice phase feeding and use some synthetic amino acids, although the exact numbers that do so are not known. Consequently, the scope for further reductions at a national level is not clear. A number of EU Member States undertake surveys of farm feeding practice, and the information gained allows them to target both research and technology transfer at those strategies that will provide the greatest improvements in NUE and reductions in N excretion at a national level. In the UK, Defra sponsors an annual survey of fertiliser practice, which provides information on fertiliser use and changes in fertiliser practice. In order to establish the scope for reducing N excretion by livestock in the UK, it is recommended that a similar survey of livestock feeding practice should be undertaken.

It is too early to attempt to quantify, with any degree of confidence, the effects on livestock numbers as a result of changes in CAP support. What does appear likely is that there will be an increase in extensive livestock production in the uplands, accompanied by some substitution of beef with sheep. For reasons discussed above, this is likely to reduce the overall efficiency of N utilisation. Undoubtedly some lowland livestock systems will intensify, with associate improvement in N utilisation, but whether this will offset the increase in extensive livestock production is not clear.

As has been demonstrated in a number of situations, strategies to improve N utilisation efficiency at a farm level may not always be synonymous with improvements at an animal level. For example, the use of forage legumes may improve N utilisation at a farm level. However, N intakes on legume silage diets tend to be higher than on grass silage diets, resulting in lower NUE when calculated per animal (page 34). The development of low protein wheat (page 38) or increasing use of home-grown proteins such as lupins, peas and beans (page 41) are unlikely to improve N utilisation by the animal, although may improve N utilisation on the farm as a result of lower fertiliser N use. It is clearly important to establish the criteria for assessing N utilisation. To improve utilisation at a farm level requires a whole-farm approach, since reduced loss from one component may be easily negated if all other components are not equally well managed. Animal excretion of manure N can be reduced by adopting the strategies outlined in this report, but poor manure collection, storage or application can easily negate any benefits gained from improved feeding practice.

30 Including certain offals, blood, bones, hair and hide.

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Many of the strategies for improving N utilisation efficiency by livestock and poultry have already been adopted by livestock farmers. AIC31 have estimated that in the period 1999 to 2005 the amount of N provided in manufactured compound feeds and blends declined from 400,523 to 334,976 tonnes. While a large proportion (0.78) of this reduction could be accounted for by reductions in livestock numbers, the nutritional improvements alone would have reduced nitrogen input by 12,232 tonnes.

Further reductions in N excretion by pigs and poultry could be achieved by enhancing the digestibility, availability and amino acid profiles of dietary proteins. In ruminants, improvements in N utilisation of 10-15% or more might be possible with more attention to protein degradability and digestibility. These improvements could be achieved through a combination of technical innovations aimed at:

a) The production of enriched microbial protein sources derived from waste productsb) The development of cheap sources of synthetic amino acidsc) The breeding of cereals, oil seeds and pulses with enhanced protein quality and quantity

characteristics.d) The breeding of forage crops that provide a better fermentable energy:degradable protein

ratio for ruminants.e) The development of methods to assess the protein degradability and fermentable energy

content of feeds for ruminants.

Taken as a whole, these developments could have a major impact on both protein self-sufficiency and the environmental impact of livestock in the UK. A number of projects have already commenced, aimed at addressing some of these objectives. However, in the short term the very cheap and plentiful supply of soyabean meal and other protein-rich by-products on world markets provides only limited incentive for industry to invest in projects aimed specifically at improving the utilisation of domestically produced proteins. Increasing use of rapeseed oil as a biofuel will result in even more oilseed protein available for use as a livestock feed. Yet prices of these commodity feeds usually bear little regard to the environmental costs of using them in intensive production systems. Consequently, the true cost of feeding large amounts of these proteins in the production of milk, meat and eggs is seriously underestimated. This situation is unlikely to improve markedly until some form of economic (e.g. pollution tax) or legislative control is applied. Only then would livestock farmers be encouraged to use better quality proteins in smaller amounts, thereby reducing import demands and N excretion. It would also set clearer targets for the industries involved in the provision of feed for animal production.

Phosphorus

Although much of the P in feeds is in a form that is largely unavailable to pigs and poultry, enzyme supplements have been developed that considerably increase the organic P utilisation. These are now widely used in non-ruminant feeds, largely because their inclusion in compound feeds is generally cost-neutral. Further developments in the efficacy of commercially available phytase enzymes and stability under a wider range of manufacturing processes is likely to see a continued reduction in P excretion by pigs and poultry. However, the potential for further reductions in P excretion by pigs and poultry is difficult to quantify because of discrepancies in estimates of the amount of phytase enzymes currently being used (Haygarth, 2004; AIC 2005). Better definition of the P requirements and the digestibility of the non-phytate P could result in further reductions in P excretion by pigs and poultry.

In contrast, ruminants are capable of capable of utilising most of the organic P in feeds. Supplementation of dairy compound feeds with inorganic P has virtually ceased, yet diets frequently provide more P than is necessary. The main reasons for this appear to be uncertainty regarding the P requirements (particularly for lactating dairy cows) and the use of high P-containing feeds.

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There is still a firmly held belief amongst dairy farmers and their advisors that reducing dietary P concentrations to levels advocated in N America and will result in reduced conception rates and fertility in dairy cows. Effects on fertility as a result of adopting lower P diets may take some years to be seen, and so further long-term research and monitoring may be necessary if dairy farmers are to be persuaded to reduce dietary P concentrations. The results of a long-term study in N Ireland are expected to show that reducing dietary P concentrations form 5.3 to 3.8 g P/kg DM can produce a 45% reduction in faecal P excretion, without compromising the health, production or reproduction of the cows (Ferris et al., 2005). As for N (above), a survey of feeding practice would provide information that could be used to estimate the scope for further reductions in P intake.

Levels of P applied to grassland (as fertiliser and manure) are generally in excess of the crops’ requirements (Withers, 2004), and there is scope for reducing fertiliser P application, with commensurate reductions in the P content of herbage. Many of the cereal-by products used in dairy cow diets also contain naturally high P contents, but their substitution with low-P feeds may incur additional expense. As with N, the market prices of these feeds take no account of their potential environmental impact.

As discussed elsewhere, many of the strategies described in this report have already been adopted by at least some producers. The decline in livestock numbers has also resulted in reductions in the amount of P fed to livestock. The annual input of P in compound feeds and blends declined from 96,320 tonnes in 1999 to 76,728 tonnes in 2005, a reduction in phosphorus input of 19,591 tonnes. AIC32 have estimated that the uptake of strategies outlined in this report alone would have reduced phosphorus input by 10,099 tonnes, equivalent to 52% of the total phosphorus saving from 1999 to 2005, with the remaining 48% of the saving due to reduced livestock numbers.

As recent report to Defra (Haygarth, 2004) concluded, there as a growing mass of information showing the potential to reduce fertiliser and feed inputs of N and P, as well as utilising manure nutrients more effectively. However, a sustained campaign of technology transfer would be necessary to achieve a voluntary uptake of some these measures. The alternative is to wait until economic or legislative controls are imposed.

32 Agricultural Industries Confederation, personal communication

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Appendices

Appendix 1. Defra-funded studies that have addressed issues related to this project include:

NT2402 Impact of nutrition and management on N and P excretion by dairy cows

WA0309 Phase feeding of pigs to reduce nutrient pollution

WA0310 Update on available knowledge of pig diets to reduce pollution and estimate costs of reducing NH3 emissions

WA0311 Modelling nitrogen and phosphorus utilisation in dairy cows

WA0314 A literature review of the effect of dietary protein level and type on fertility in dairy cows

WA0315 A review of European phosphorus requirements for dairy cows

WA0316 Synchronising ruminal supply of energy and nitrogen to decrease the production of waste nitrogen in dairy cows

WA0317 Phase feeding pigs to reduce nutrient pollution

WA0320 Development of a decision support system to evaluate methane, nitrogen and phosphorus outputs from dairy cows

WA0321 A review and Workshop to agree advice on reduced nutrient pig diets

WA0322 A review of nitrogen utilisation efficiency in the dairy cow, and what milk producers can do now to improve it

ES0201 Reviewing the Potential for Reductions of Nitrogen and Phosphorus Inputs in Current Farm Systems: A Specification of Project Requirements

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Appendix 2. The calculation of protein and phosphorus requirements.

The principle used to estimate the theoretical protein requirements for livestock in England and Wales was to calculate the daily requirement according to AFRC (1993) and NRC (2001, 1998, 1994, 1985) for an individual animal as defined in the DEFRA livestock numbers survey. The daily estimates were scaled according to total animal numbers and their typical life span if shorter than 1 year. The following assumptions were made to relate calculations of requirements to the DEFRA livestock numbers survey:

Dairy animals:Mature milking cows were assumed to be 600kg in weight and to yield 6400 litres of milk over 365 days. Mean milk quality was assumed to be 3.25% protein, 3.8% milk fat and 4.75% lactose. The typical cow was assumed to be 55 days pregnant. Heifers in calf over 2 years old were described as 540kg in weight and 130 days pregnant, gaining 0.3kg daily in addition to pregnancy.Heifers in calf between 1 and 2 years old were described as 350kg in weight and 50 days pregnant, gaining 0.7kg daily in addition to pregnancy.Heifers not pregnant but over 2 years old were assumed to be 540 kg in weight and gaining 0.2 kg daily.Heifers not pregnant between 1 and 2 years old were assumed to be 350 kg in weight and gaining 0.7 kg daily.Calves less than 1 year old were assumed to be 100 kg in weight and gaining 0.6 kg daily.

Beef Animals:Mature beef cows were assumed to be 550kg in weight and to yield 1825 litres of milk over 365 days. Mean milk quality was assumed to be 4% protein, 5% milk fat and 4.75% lactose. The typical cow was assumed to be 55 days pregnant. Heifers in calf over 2 years old were described as 470kg in weight and 130 days pregnant, gaining 0.2kg daily in addition to pregnancy.Heifers in calf between 1 and 2 years old were described as 350kg in weight and 100 days pregnant, gaining 0.5kg daily in addition to pregnancy.Heifers not pregnant between 1 and 2 years old were assumed to be 340 kg in weight and gaining 0.5 kg daily.Calves less than 1 year old were assumed to be 125 kg in weight and gaining 0.75 kg daily.

Sheep:Mature lactating ewes were assumed to be 55kg in weight and to yield 2kg milk daily in the first month of lactation followed by 1.7, 1.05 and 0.4 in months 2, 3, and 4 respectively. Lambs for meat production were assumed to have a 6 month lifecycle with a finishing weight of 45kg.

Pigs:The mean daily crude protein requirement for lactating sows was assumed to be 852 g/day for a 6 week lactation. The mean daily crude protein requirement for gestating sows was assumed to be 233 g/day for the entire pregnancy. Non-pregnant animals including boars were assumed to require 395g CP daily.

Poultry:Layers were assumed to require a 16% crude protein diet at 80g daily dry matter intake. Broilers and other poultry were described as requiring a 21.5% protein diet at 170g/day daily intake. Turkeys were described as requiring a 21% protein diet at 570g/day daily intake.

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Appendix 3: Raw material usage in the production of animal feedingstuffs in Great Britain in 2002, and estimated supply of nitrogen (N33) and phosphorus (P) ('000 tonnes).

Source: Defra Statistics

Tonnes N P

Barley 728.6 12.3 2.51Citrus and other fruit pulp 63.4 0.7 0.06Confectionery by-products 125.4 2.2 0.22Distillery by-products 204.8 9.1 1.75Dried Sugar Beet Pulp 181.8 2.9 0.25Field Beans 102.1 4.1 0.8Field Peas 62.2 2.3 0.3Fish meal 149.1 15.8 4.1Maize gluten feed 475.1 15.1 4.2Minerals 404.6 0.0 27.8Molasses 284.8 2.4 0.3Oats 23.5 0.4 0.1Oil and fat 227.5 0.0 0.0Oilseed rape cake and meal 520.8 28.6 5.5Other cereals by-products 162.0 3.5 1.0Other materials 276.2 4.8 1.4Other meal 7.0 0.6 0.3Other oilseed cake and meal 453.0 22.3 3.6Poultry meal 3.1 0.3 0.0Protein concentrates 19.7 1.1 0.3Rice bran extractions 26.2 0.6 0.4Soya cake and meal 1 010.1 76.4 7.3Sunflower cake and meal 272.3 14.6 2.9Wheat 2 758.5 51.2 8.3Wheat feed 886.1 21.3 9.1Whole and flaked maize 79.5 1.1 0.2Whole Oilseeds 60.2 3.8 0.3

Total used in the manufacture of compounds and blends

9 567.8 297.4 82.9

Straight concentrates (a) 5 925 140.8 26.7Non-concentrates (b) 525 11.7 1.4Inter/intra farm sales 3 071 59.7 13.8Total 'other concentrate feeds' 9 521 212.2 41.9

Total all purchased feedingstuffs 19 089 509.6 125

(a) i.e. cereals, cereal, offal, proteins and other high energy feeds(b) Non-concentrates expressed in terms of equivalent tonnage of high-energy feeds).

NB: This does not include cereals fed on farm

33 N content calculated from typical crude protein concentrations/6.25

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Appendix 4: UK imports of Animal Feedingstuffs (‘000 tonnes): average per year for the period 1998 - 200034.

Product type Tonnes % of total

Product description Tonnes % of product

type

Oil cake Total 2 491 58.3 Soya beans 1 404 56.4Sunflower 493 19.8Palm nut or kernels 300 12.0Rape seed 144 5.8Coconut or copra 50 2.0Cotton seeds 42 1.7Groundnuts 24 1.0Linseed 4 <1.0Other oil seeds and oleaginous plants

31 1.2

Compound feeds 914 21.4Flours, meals and pellets derived from animals, fish and birds, unfit for human consumption

261 6.1 From fish, crustaceans, molluscs or other aquatic invertebrates

245 93.9

Meat or meat offal (including tankage); greaves

17 6.1

Vegetables residues and by-products

178 4.1

Residues of brewing and distilling

174 4.1

Residues of starch manufacture

86 2.0

Brans, sharps and other residues

80 1.9 Wheat 59 73.7Other cereals 12 15.0Maize 9 11.2Legumes 0.3 <1.0Rice 0.2 <1.0

Hay and fodder 55 1.3 Lucerne meal and pellets

23 41.8

Cereal straw and husks 20 36.4Swedes, mangold and other forage crops

12 21.8

Residues of sugar manufacture

29 0.7

Total 4 274

34 Data prepared by Statistics (Commodities & Food) Accounts and Trade, ESD, DEFRA

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Appendix 5. Area of British grassland by class type.

‘000 ha

Class/sub-class England Wales Scotland Great Britain

Improved grassland 3196 774 1033 5003

Permanent pasture 2375 644 712 3731

Temporary leys <5 years old 643 128 321 1092

Set aside 178 2 0.5 180

Semi-natural grassland 1656 631 1519 3806

Neutral grass 500 135 441 1076

Acidic grass 279 318 851 1448

Calcareous grass 788 147 129 1064

Bracken 71 29 98 198

Fen, marsh swamp 18 2 0.1 20

Mountain, Heath and bog 482 145 3079 3706

Dense dwarf shrub heath 133 58 516 707

Open dwarf shrub heath 132 55 1685 1872

Bog (deep peat) 106 6 402 514

Montane habitats 0 0 397 397

Inland bare ground 111 26 79 216

Total 5334 1550 5631 12515

Footnote: adapted from the data of the Countryside survey LCM (Land Coverage map), DEFRA 2002; SEERAD 2003.

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Appendix 6. Estimated annual dry matter (DM) yields from British Grasslands.

‘000 tonnes

Class/sub-class DM yield (t/ha)

England Wales Scotland Great Britain

Improved grassland 24 054 5 920 8 516 38 490

Permanent pasture 3-12 (7 ) 1 6625 4 508 4 984 26 117

Temporary leys (<5years) 4 -15 (11)

7 073 1 408 3 53112 012

Set aside 1-3 (2) 356 4 1 361

Semi-natural grassland 4 024 1 561 3 928 9 513

Neutral grass 2-6 (3.5) 1 750 472. 1 543 3 765

Acidic grass 1-4 (2.5) 697 795 2 127 3 620

Calcareous grass 2.0 1 576 294 258 2 128

Bracken - - - - -

Fen, marsh swamp 1.5 27 3 0

Mountain, Heath and bog 742 238 5 405 6 386

Dense dwarf shrub heath 1.5-3 (2) 266 116 1 032 1 414

Open dwarf shrub heath 1.5-3.5 (2)

264 110 3 370 3 744

Bog (deep peat) 2.0 212 12 804 1 028

Montane habitats 0.5 0 0 199 200


Total 28 820 7 719 17 849 54 389

Values in parenthesis = assumed averagesReferences: Permanent pasture; Morrison et al., 1980, Hopkins et al., 1990, Baker, 1986, Munro and Davies 1974?) based on fact that most old Permanent Pasture receives less than optimum fertiliser, and most is for grazing rather than conservation. Values for Temporary leys: Hopkins et al., 1995; Munro and Davies, 1974; Frame and Newbold , 1984; Corrall, 1984;Hopkins, 2000; Morrison et al., 1980 , based on average fertiliser application to temporary leys in England and Wales being 200kg/ha (Hopkins, 2000; Hopkins et al., 1984; Morrison et al.,1980) and that of 40% of old sward more than 20 years old being <50kg/ha (Hopkins, 2000; Baker, 1986; Hopkins and Hopkins.,1994, Morrsion et al., 1980) Rough grazing, (Rawes, et al. (1961) Davies and Munro, (1974), Milton and Davies, (1940)

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Appendix 7. Estimated annual N yield from British grassland

‘000 tonnes

Class/sub-class N content (tN/tDM)

England Wales Scotland GB

Improved grassland 611.19 150.43 225.55 987.168 Permanent pasture 0.024 399 108.19 119.62 626.832Temporary leys (<5years)

0.03 212.2 42.24 105.93360.39

Semi-natural grassland

87.66 31.20 79.89 198.75

Neutral grass 0.025 43.75 11.80 38.58 94.15

Acidic grass 0.017 11.85 13.52 36.16 61.52

Calcareous grass 0.02 31.52 5.88 5.16 42.56

Bracken - - - -

Fen, marsh swamp 0.02 0.54 0.06 0.00 0.62

Mountain, Heath and bog

15.37 4.99 112.50 132.86

Dense dwarf shrub heath

0.021 5.59 2.44 21.67 29.715

Open dwarf shrub heath

0.021 5.54 2.31 70.77 78.645

Bog (deep peat) 0.02 4.24 0.24 16.08 20.56

Montane habitats 0.02 0.00 0.00 3.98 3.98


Total 714.22 186.61 417.94 1318.78

Nitrogen content : Davis and Munro (1974), Grant (1971), Milne and Grant (1977), Milton (1940), Rawes (1961), NRC Nutrient Requirements of Horses (1989) MAFF (1992)

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Appendix 8. Estimated annual P yield from British grassland

‘000 tonnes

Class/sub-class P content (tP/tDM)

England Wales Scotland Great Britain

Improved grassland 65.51 15.96 23.55 105.2 Permanent pasture 0.0026 43.23 11.72 12.96 67.91

Temporary leys (<5years)

0.003 21.22 4.22 10.59 36.04

Set aside 0.003 1.07 0.01 0 1.08

Semi-natural grassland

9.71 3.44 8.97 22.13

Neutral grass 0.003 5.25 1.42 4.63 11.30

Acidic grass 0.0018 1.25 1.43 3.83 6.52

Calcareous grass 0.002 3.15 0.59 0.52 4.26

Bracken - - - -

Fen, marsh swamp 0.002 0.05 0.01 0.00 0.06

Mountain, Heath and bog

2.23 0.79 17.91 20.92

Dense dwarf shrub heath

0.003 0.80 0.35 3.10 4.25

Open dwarf shrub heath

0.0038 1.00 0.42 12.81 14.23

Bog (deep peat) 0.002 0.42 0.02 1.61 2.06

Montane habitats 0.002 0.00 0.00 0.40 0.40

Inland bare ground 0.00 0.00 0.00 0.00

Total 77.45 20.19 50.43 148.07

Phosphorous content references, as for Nitrogen.

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Appendix 9. Estimated DM, N and P production from conserved forages in GB in 2002.

000' tonnes

DM

N % of total N P % of total P

‘000 tonnes ‘000 tonnes

Grass silage 9 630 246.5 72 28.9 65

Grass hay 2 564 44.1 12.8 7.6 17

Maize silage 1 454 23.3 6.7 3.8 8.6

Straw 355 2.5 0.66 0.4 0.9

Whole crop silage 163 2.5 0.66 0.4 0.9

Other forage crops 1 043 25 7.3 3.1 7.6

Total conserved 15 209 343.9 44.2

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Appendix 10. Theoretical reductions in N loss from ewes and lambs on ‘high sugar’ grass (HSG) compared with conventional (CG) ryegrass swards*

Sward type HSG CG

DMI (kg/d) 0.840 0.840NI (g/d) 30.64 30.64NI over 184d 5.638 5.638Lamb DLWG (kg) 0.224 0.196Total lamb N gain (g/d) 5.1 4.58N ‘loss’ (g/d) 25.54 26.06NUE (%) (lamb N gain/N intake) 16.6 14.9N ‘loss’ (kg)over 184 days 4.7 4.8N ‘loss’ UK flock (t/per 184 days) 81 357 83 088Difference in N loss (UK flock) (CG-HSG )(t) 1 731% reduction in N loss over 184 grazing trial by feeding HSG

2.1%

Additional N loss from CG grazed lambs 1

Difference in live weight at end of 184 d between HSG and CG lambs HSG-CG (kg)

5.07

No of days at DLWG of 0.196kg/dFor additional 5.07 kg of LWG by CG lambs

26

N ‘lost ‘ (kg) in 26 days per lamb at a loss of 26.06g N/d

0.677

N ‘lost’ by UK lamb flock in 26 days (t) 11 719

Total difference in N ’loss’ (t) from HSG and CG lambs at same final live weight (UK flock)

13 450

% reduction in total N loss from animals grazing HSG

14.2

*Based on unpublished data of Evans et al , of a trial run over 184 days with ewes and lambs grazed on HSG or CG swards from 31st March until 29th June, and then the weaned lambs grazed on the two swards until September 30th Data is for the lambs only, averaged over the 184 day trial. N contents of both of these varieties grown in experimental plots managed for grazing averaged over the season were 3.65%, and are used in the calculation of N intakes and outputs. Assumed DM intakes of lambs to be 3.5.% of LW ( as DM) /d.(AFRC 1993)., and was assumed to be the same for the two swards, as has been reported elsewhere (Lee et al;2001) Average N gain calculated from standard equations (AFRC 1993) Total UK lamb flock under 1 year old in 2002, 17.31 million, breeding ewes, 17,628 million (DEFRA 2002).

1. 98% of the HSG lambs finished by the end of the trial, whereas only 68% of those fed CG were finished, with 32% being sold as stores. The estimated extra N ‘lost’ from CG animals being grown to the same weight as the HSG lambs is given in this and subsequent rows of this table.

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Appendix 11. Theoretical reduction in N loss from feeding finishing beef steers on high sugar grass (HSG) a control grass (CG) or permanent pasture (PP).

Sward type

HSG CG PPDMI (kg/d) 7.5 8.04 7.98

NI (g/d) 180 191 252

Steer DLWG (kg) 1.12 0.95 1.2

Total steer N gain (g/d) 20.93 18.02 22.83

N ‘loss’ (g/d) 159 173 229

NUE (%) (steer N gain/N intake) 11.6 9.42 9

NI over 180d (kg) 32.4 34.38 45.36

N ‘loss’ (kg)over 180days 28.62 31.14 41.22

N ’loss’ to same live weight per steer1 31.164 39.44 41.22

N ‘loss’ by UK herd to same live weight 68 654 86 895 90 808

% reduction in total N loss from steers grazing HSG 21 24

1 The growth rate of the HSG steers was slightly lower than that of the PP fed animals (0.08 kg/d) whereas that of the CG –grazed animals was substantially reduced compared with the PP (0.25kg/d). A further 16 and 48 days were required by steers grazing HSG and CG, respectively, to attain the same finished live weight as those grown on PP. Therefore the calculations in this and subsequent rows on the table are for the extra N loss that would accrue from growing the HSG and CG animals on to the same finishing weight.

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Appendix 12. Theoretical reductions in N ‘loss’ to the environment from the 2002 beef herd from grazing High Sugar Grass (HSG) vs. Permanent pastures (PP).

Animal category (‘000 head) Total N Loss (t) over 180d.

Reduction in N loss through feeding HSG

(t/180d)HSG PP

Finished beef1 (2203) 84 991 109 269 24 278

Beef cows2 (1673) 77 359 104 043 26 684

In-calf beef heifers (>2 yr.) 3 (75) 7 247 9 548 2 301

In-calf beef heifers (<2 yr.) 4 (95) 3 225 4 147 922

Total N Loss 172 822 227 007

Total reduction in loss (t) - - 54 184

Total % reduction in N loss 24

1. Data extrapolated from unpublished data of Davies et al on spring calved beef steers finished off HSG swards or permanent pastures giving the same production response (ca. 1 kg LWG/d). NUE from this study used for the other categories of beef cattle. Assumed to average 460 kg over the 180d, and fed at 2% of BW as DM/d. N required = 162 g N/d.

2. Assumed to average 600kg, fed at 2%BW (as DM)/d. N requirements of 220g/d, (NRC, 1996), to be a 50:50 mixture of’ ‘average’ and ‘high’ yielding cows

3. Assumed to average 520 kg N req. 167g/d, fed at 2.2% BW (as DM) /d, ( NRC, 1996)4. Assumed to average 400 kg, N req. of 116g/d, fed at 2.2% BW (as DM)/d, expected to gain

650g/d before calving and 200g/d post-calving. (Adapted from NRC 1996)

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Appendix 13. Theoretical reductions in excess supply of N to the 2002 UK beef herd, when high sugar grass (HSG) sward was grazed vs. permanent pasture (PP).

Number of head (000) Excess to requirements.(t N) % Excess to requirements

HSG PP HSG PPFinished beef1 (2203) 30 930 54 723 48 85

Beef cows2 (1673) 20 478 46 979 31 71

In-calf beef heifers (>2yrs)3 (175) 1629 2531 82 227

In-calf beef heifers (<2 yrs) 4 (95) 2689 4768 47 184

Total N excess 55 726 109 001 40 79

Total requirement 137 739 -

Total % reduction in N excess 51

1,2,3,4 details as for Appendix Table 3

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Appendix 14.. Theoretical reductions in N loss from the 2002 UK beef herd, when grass silage (GS) was substituted with 33, 67 or 100 % Maize silage (maize silage) when offered to finishing beef steers (424-570kg) or to the remaining beef-herd for 180d.

Animal category (‘000 head)

Total N Loss (t) over 180d.

GS 100 GS 67 MS 33 GS 33 MS 67 MS 100

Finished beef1 (2203) 61 270 54 810 52 122 51 021

Difference 6 -6 460 -9 148 -10 249

Beef cows2 (1673) 86 443 76 255 66 280 62 0805

Difference -10 188 -20 163 -24 363

In-calf beef heifers 3 (>2yrs) (175) 8 550 7 672 6 599 5 716

Difference -828 -1 851 -2 834

In-calf beef heifers 4 (<2 yrs) (95) 3 599 3 175 2 758 2 373

Difference -424 -841 -1 226

Total N Loss 159 862 141 912 129 759 121 190

Total reduction in loss (t) - 17 950 30 103 38 672

Total % reduction in N loss 0 11 19 24

1, 2, 3, 4 details as for Appendix Table 3.5. MS diets unable to meet lactating beef cows protein requirement when fed at 2% BW a further 2

650 t N required by the beef cow herd for MS silages containing 11 %CP. Thus these cows would need , 0.5 kg 30% CP concentrate per day per animal and 11.5kg MS/d.

6. Difference = GS- MS:GS mix, or GS-MS

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Appendix 15. Theoretical reductions in excess supply of N to the 2002 UK beef herd, when grass silage is substituted with maize silage.

Assumptions: 33, 67 or 100 % Maize silage (MS) when offered to finishing beef steers (424-570kg) or to the remaining beef-herd for 180d.

Animal category (‘000 head) Excess N to requirements.GS 100 GS 67 MS 33 GS 33 MS 67 MS 100

Finished beef 1 (2203) 28 551 19 738 10 927 2 996

Beef cows 2 (1673) 27 705 17 668 7 395 3 012

In-calf beef heifers 3 (>2yrs) (175) 1 928 1 510 1 080 663

In-calf beef heifers 4 (<2 yrs) (95) 4 353 3 175 2 072 1 109

Total excess N (t) 62 537 42 091 21 474 7 780

% Excess relative to requirements 45 30 16 5.6

1,2,3,4 details as for Appendix Table 3

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Appendix 16. Annual N balances for arable and forage crops in the UK. [After Sylvester-Bradley (1993), but brought up-to-date and augmented. Fixed N is inferred from crop N contents and residual soil N at harvest. N exports & imports relate to all UK agriculture].

Crop Area N input(applied or fixed)*

Yield N content N off-takeat harvest

N balance(input-offtake)

N exported(from agriculture)

Net N input

'000 ha kg/ha t/UK t/ha kg/t kg/ha t/UK kg/ha t/UK t/UK t/UKWinter wheat-feed, seed, export, etc. 1 074 187 200 806 7.9 17.0 134 144 215 52 55 839 15% 21 632 179 174Winter oilseed rape 366 207 75,824 3.2 30.0 96 35 165 112 41 026 0% 0 75 824Winter wheat-milling 694 209 144 690 7.3 19.0 139 96 252 69 47 536 75% 72 189 72 501Winter barley-feed, seed, export, etc. 455 155 70 486 6.4 17.0 109 49 477 45 20 464 0% 0 70 486Winter field beans 147 285 41 865 3.8 42.0 158 23 136 125 18 362 20% 4 627 37 238Spring barley-feed 299 101 30 085 5.8 17.0 98 29 261 1 150 0% 0 30 085Sugar beet 271 119 32 139 4.9 14.0 68 18 415 49 13 154 20% 3 683 28 456Peas-combining 170 105 17 717 55.0 1.7 94 15 852 10 1 611 0% 0 17 717Spring barley-malting 116 143 16 561 5.4 14.0 76 8 755 68 7 875 20% 1 751 14 810Winter barley-malting 61 265 16 108 3.6 35.0 126 7 659 140 8 510 20% 1 532 14 576Potatoes maincrop 135 155 20 858 45.0 2.5 113 15 188 40 5 333 90% 13 669 7 189Spring oilseed rape 41 134 5 454 2.2 33.0 73 2 955 69 2 808 0% 0 5 454Peas-vining 46 165 7 522 4.8 11.0 52 2 382 110 5 015 100% 2 382 5 140Winter oats 84 109 9 140 6.0 17.0 102 8 553 9 755 55% 4 704 4 436Spring wheat-milling 55 132 7 217 5.8 20.0 115 6 287 17 929 75% 4 716 2 501Spring oats 36 109 3 917 5.0 17.0 85 3 055 24 863 55% 1 680 2 237Potatoes-seed 13 120 1 560 32.0 3.5 112 1 456 10 130 0% 0 1 560Triticale 14 87 1 230 6.0 18.0 108 1 535 -24 -334 0% 0 1 230Potatoes-early 8 194 1 548 30.0 3.5 105 840 94 748 100% 840 708Linseed 25 60 1 486 1.4 38.0 53 1 329 5 112 100% 1 329 157Rye 8 87 711 5.8 18.0 104 851 -19 -152 100% 851 -140Arable crops 4 117 706 924 472 619 230 732 135 585 571 339Other crops incl. hortic. & setaside 989Total cropping 5 106Grass grazing 6 198 80 495 858 61.7 4.8 293 1 816 329 25 154 956 0% 0 495 858Grass silage 425 140 59 523 46.3 5.8 266 113 265 75 31 888 0% 0 59 523Grass hay 188 100 18 827 12.9 19.3 249 46 812 -115 -21 651 0% 0 18 827Forage Maize 120 50 6 000 40.0 5.3 211 25 344 -105 -12 600 0% 0 6 000Other forage cropsTotal Forage 6 932 580 209 2 001 749 152 592 0 580 209Total UK Crops and Forage 11 134 1 287 132 383 324 383 324 135 585 1 131 921

* N imports for forage crops have not been adjusted for N fixation. It will be best to assume the same N efficiency as for fully fertilised crops.

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