the effects of growth temperature on digestibility and fibre concentration of seven temperate grass...
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ORIGINAL ARTICLE
The effects of growth temperature on digestibility and fibreconcentration of seven temperate grass species
GUDNI THORVALDSSON1, GAETAN F. TREMBLAY2 & H. TAPANI KUNELIUS3
1Agricultural University of Iceland, Keldnaholti, Iceland, 2Agriculture and Agri-Food Canada, Soils and Crops Research and
Development Centre, Sainte-Foy, Quebec, Canada, and 3Agriculture and Agri-Food Canada, Crops and Livestock Research
Centre, Prince Edward Island, Canada
AbstractThe effects of growth temperature on digestibility and fibre concentration of seven grass species: Kentucky bluegrass (Poapratensis L), timothy (Phleum pratense L), meadow foxtail (Alopecurus pratensis L), perennial ryegrass (Lolium perenne L), redfescue (Festuca rubra L), tufted hair-grass (Deschampsia caespitosa L (PB)) and meadow fescue (Festuca pratensis Huds) wereinvestigated in growth chamber and greenhouse experiments. Seedlings from each grass species were established in agreenhouse and then transferred at five weeks of age to three growth chambers with day/night temperatures of 9/5, 13/9 and17/138C, respectively. Three pots of each species from each temperature treatment, and from the greenhouse control, wereharvested weekly for three weeks. The rate of decline of in vitro true digestibility (IVTD) and in vitro cell wall digestibility(IVCWD) increased with increasing temperature for all species. Each degree of increase in temperature decreased the IVTDby an average of 0.22 g kg�1 dry matter (DM) day�1 between 9 and 138C, and by 0.35 g kg�1 DM day�1 between 13and 178C. On average, the neutral detergent fibre (NDF) increased at a rate of 0.78 g kg�1 DM day�1 for each degreeincrease in temperature between 9 and 178C. The effects of temperature were less for perennial ryegrass and meadow fescuethan for the other species. Perennial ryegrass was consistently ranked as highest in digestibility, followed by meadow fescue;tufted hair-grass had the lowest digestibility. The rate of decline in digestibility was slower for perennial ryegrass andmeadow fescue than for the other species.
Keywords: IVTD, IVCWD, NDF, ADF, hemicellulose, grasses.
Introduction
The digestibility of herbage is directly related to
species (Minson et al., 1964), harvest date (Thor-
valdsson & Andersson, 1986; Kunelius & McRae,
1986) and temperature (Deinum et al., 1968). Grass
species differ both in maximum digestibility at early
growth stages and in the rate of decline in digest-
ibility with advancing maturity. Young, immature
forage plants are highly digestible but the digest-
ibility declines with maturity. The rate of decline in
digestibility of forage species is influenced by cli-
matic factors, especially temperature. The tempera-
ture effect is both direct, by affecting the cell wall
digestibility (Deinum & Dirven, 1976; Moir et al.,
1977), and indirect, by modifying phenological
development (Smith & Jewiss, 1966; Dirven &
Deinum, 1977; Ford et al., 1979). Although the
cellular content of forage plants is almost totally
digestible, there is great variation in cell wall digest-
ibility (van Soest, 1967). The digestibility of forage
plants depends, therefore, mainly on the cell wall
components and their digestibility. The main com-
ponents in the cell wall are cellulose, hemicellulose
and lignin (Deinum, 1981). Cellulose in young
grasses is almost completely digested by ruminants,
but lignification decreases digestibility with in-
creased maturity. Hemicellulose is composed of a
mixture of different polymers which vary in digest-
ibility, whereas lignin is resistant to rumen fermenta-
tion.
Even though it is known that temperature affects
digestibility and cell wall content, these effects have
not been well quantified. The objective of this study
was to quantify the effects of increasing temperature
on the plant growth, nitrogen concentration,
Correspondence: G. Thorvaldsson, Agricultural University of Iceland, Keldnaholti, 112 Reykjavık, Iceland. E-mail: [email protected]
Acta Agriculturae Scandinavica Section B-Soil and Plant Science, 2007; 57: 322�328
(Received 28 March 2006; accepted 11 August 2006)
ISSN 0906-4710 print/ISSN 1651-1913 online # 2007 Taylor & Francis
DOI: 10.1080/09064710600984221
digestibility and fibre concentration of seven diverse
grass species, including species widely used in cool
temperate regions of Europe and North America, as
well as wild species. The effects of growth tempera-
ture on the dry matter (DM) yield and nitrogen
concentration have been documented previously
(Thorvaldsson & Martin, 2004; Thorvaldsson &
Kunelius, 2005).
Material and methods
Species and soil
In spring 2001, seven cool-season grass species were
sown in pots in a greenhouse at the Nova Scotia
Agricultural College, Truro, NS, Canada (45822? N,
63816? W) according to species-specific germination
times and growth rates (Table I). Seeds of meadow
fescue and perennial ryegrass were seeded six days
later than originally planned due to late receipt of
seed. A peat-based growing medium (Pro-Mix BX
from Premier Horticulture Ltd., QC) consisting of
Canadian sphagnum peat moss (80%), perlite,
vermiculite, dolomitic and calcitic limestone was
used. Three or four seeds were placed in each of
nine equally distributed 2 mm deep holes in each
pot. Each pot was 127 mm in diameter at the top,
90 mm at the bottom and 118 mm deep.
After emergence, seedlings were thinned to nine
plants per pot. Seedling establishment was good for
all species except tufted hair-grass which had poor
seed germination. On 22 May, 2 June and 14 June,
each pot received 0.064 g N, 0.028 g P and 0.051 g
K with trace amounts of boron (B), copper (Cu),
iron (Fe), manganese (Mn), molybdenum (Mo) and
zinc (Zn). The species, cultivars, their origins,
seeding dates and emergence dates are given in
Table I.
Experimental design
At the beginning of the treatment period (19 June or
20 June) three pots of all grass species were
randomly selected and harvested. On the same
dates, nine pots (3 harvest dates�/3 pots) of each
species were randomly selected from the greenhouse
and moved into three growth chambers with day/
night temperatures of 9/5, 13/9 and 17/138C,
respectively. Day length was set at 19 h as most
cultivars used were from regions with long summer
days. The pots were rotated two to four times weekly
during the experimental period. Three pots of each
grass species and growth chamber, and three pots of
each species from the greenhouse control, were
harvested weekly for three weeks. The greenhouse
control provided light and temperature conditions
more similar to outdoor conditions. Such control
gives information about the conditions in the growth
chambers, whether they are far from or close to the
conditions in the greenhouse. In the greenhouse,
D. caespitosa was harvested in the last week only due
to poor germination in some pots.
The three pots of the same treatment were treated
as independent samples in the statistical analysis,
although they were together in one chamber. Any
differences between chambers other than those due
to temperature were confounded with temperature.
Deviation in chamber temperature from the assigned
temperature was small, but other sources of devia-
tion can not be excluded due to the chambers not
being replicated.
The daily change in digestibility and fibre fractions
was found by calculating the difference between
subsequent measurements divided by the number of
days between observations.
The influence of each degree change in tempera-
ture, for the whole treatment period, was found by
calculating the difference between observations (di-
gestibility or fibre) from growth chambers with
different temperatures divided by the number of
degrees between the temperature treatments. The
daily effects of temperature were found by dividing
by the length of the temperature treatment (number
of days).
Statistical analyses were carried out by GenStat†
(Genstat 5 Committee 1993). Differences between
growth chambers and between species were tested
for statistical significance on data from the last
Table I. Species, cultivar, origin, seeding date and date of first emergence.
Species Common name Cultivar Origin Seeding date Date of first emergence
Alopecurus pratensis L. Meadow foxtail Seida Norway 8 May 14 May
Deschampsia caespitosa L. Tufted hair-grass Unnur Iceland 3 May 10 May
Festuca pratensis Huds. Meadow fescue Norild Norway 16 May 22 May
Festuca rubra L. Red fescue Samur Iceland 7 May 13 May
Lolium perenne L. Perennial ryegrass Svea Sweden 16 May 21 May
Phleum pratense L. Timothy Adda Iceland 9 May 13 May
Poa pratensis L. Kentucky bluegrass Fylking Sweden 2 May 9 May
Temperature effects in grasses 323
harvest date. Additionally, the greenhouse treatment
was also analysed for each harvest date separately.
Growth chambers
Two of the growth chambers were 185 cm�/77 cm.
The third growth chamber, which maintained the
highest temperature, was a different type and mea-
sured 248 cm�/125 cm. Lighting was provided by
cool-white fluorescent tubes, supplemented by in-
candescent bulbs. The lights were set at 90�100 cm
above the floor of the chambers and adjustments to
ensure consistent conditions were made by moving
the lights up or down. Light level was measured
weekly with an LI COR quantum sensor, which
measures photosynthetically active radiation in the
400�700 nm wave band. For the experimental per-
iod, light measurements at leaf height averaged
152 mmol m�2 s�1.
The temperature was measured in the middle of
the chambers, 17.5 cm above the rim of the pots,
twice during the day and once at night; average day
temperatures in each growth chamber and for each
week are provided in Table II. Night temperatures
were maintained at 5, 9 and 138C. Relative humidity
in the growth chambers was about 80% at 98C, 70%
at 138C and 60% at 178C. Plants were watered daily,
as required.
Chemical analysis
Neutral detergent fibre (NDF) and acid detergent
fibre (ADF) concentrations in forage samples were
determined with an ANKOM Fiber Analyzer F 200
(Ankom Technology Corp., Fairport, NY) as out-
lined in ANKOM technology procedure 05/03.
The in vitro true digestibility (IVTD) was deter-
mined according to the method of Goering and Van
Soest (1970) based on a 48-h rumen fluid digestion
followed by a NDF determination of the post-
digestion residues. The rumen fluid digestion was
performed using Ankom F57 filter bags, a Daisy II
incubator, and the filter bag method recommended
by Ankom Technology (Fairport, New York, USA).
Rumen fluid was obtained from a lactating ruminally
fistulated dairy cow fed a good quality cool-season
grass mixture of silage, corn and barley grain and a
protein supplement according to the cow’s require-
ments. The animal was cared for according to the
guidelines of the Canadian Council on Animal Care
(1993). The in vitro cell wall digestibility (IVCWD)
was calculated for NDF values as follows: IVCWD
(g kg�1 NDF)�/1�/(post-digestion NDF dry weight/
pre-digestion NDF dry weight)�/1000.
Results and discussion
Plant development
Most grass species were approximately 30 cm tall at
the beginning of the temperature treatment, but red
fescue was only 14 cm and Kentucky bluegrass
23 cm tall. Meadow foxtail was the tallest species
at 37 cm. Plant height increased significantly with
increasing temperature; differences among species
were also significant (data not presented).
Most species had 2�3 leaves per tiller at the
beginning of the temperature treatment, except
tufted hair-grass and meadow fescue which had 1�2 leaves. The plants remained in a vegetative state for
most of the experiment. By the last harvest date a
few nodes were apparent on some plants of Ken-
tucky bluegrass, meadow foxtail, tufted hair-grass
and meadow fescue. In the case of Kentucky blue-
grass, a few nodes were also present on 3 July for
plants grown in the greenhouse and on 10 July in the
138C and 178C growth chambers. Two timothy
tillers had formed heads in the greenhouse by the
last harvest date. The probability of reproductive
growth was low because the plants were grown from
seeds and were not exposed to cool temperature or
short days.
Both the growth rate and DM accumulation in
this experiment were good (Thorvaldsson & Martin,
2004).
Temperature and fibre
The concentration of NDF, ADF and hemic-
ellulose in the seven grass species was rather low
(Tables III, IV). Perennial ryegrass was generally
lowest in NDF, followed by meadow fescue. The
increase in NDF concentration with maturity in the
greenhouse was on average 0.36 g kg�1 DM day�1,
being lowest for Kentucky bluegrass and timothy,
and highest for red fescue and tufted hair-grass.
These results are within the usual range found in
field experiments in the cool temperate regions of
Table II. Average weekly day temperature (8C) in the three
growth chambers.
Week
Temperature
day/night (8C)
Growth chambersz
Greenhousey
9/5 13/9 17/13
1 9.4 13.0 16.5 21.8
2 9.5 13.1 17.4 21.7
3 9.4 13.2 17.1 19.8
Average 9.4 13.1 17.0 21.1
zAverages including night temperatures are 0.88C less.yAverage of day and night temperatures.
324 G. Thorvaldsson et al.
Europe and North America (Hidiroglou et al.,
1966; Valberg & Bo, 1972; Aman & Lindgren,
1983; Kunelius & McRae, 1986; Lindberg &
Lindgren, 1988). On average, the proportion of
ADF/NDF was a little above 50% but increased
slightly over time. In general, two species, timothy
and Kentucky bluegrass, had a higher proportion of
ADF than the others.
The temperature effect on fibre content was clear
for all species: increased temperature increased the
content of all fibre fractions. The NDF content
increased by an average of 0.78 g kg�1 DM day�1
(0.078 per cent units) for each degree increase in
temperature from 9 to 178C for all species (Table V).
The temperature coefficient for ADF was 0.52 g
kg�1 NDF day�1 (0.052 per cent units) and
0.29 g kg�1 NDF day�1 (0.029 per cent units) for
hemicellulose. The temperature effects on NDF
were highest for meadow fescue, timothy and
perennial ryegrass. These species, as well as Ken-
tucky bluegrass, also had a high temperature coeffi-
cient for ADF. For hemicellulose, the temperature
coefficients were lowest for Kentucky bluegrass and
red fescue but similar for the other species.
Ford et al. (1979) studied the effect of growth
temperature on lignin, hemicellulose and cellulose
concentrations in tropical and temperate grasses. In
temperate grasses, all these components showed a
consistent increase with growth temperature. Similar
results have been found for fibre in many other
studies (Alberda, 1965; Deinum, 1966; Smith,
1970; Allinson, 1971; Wilson et al., 1976). Small
effects of temperature on fibre concentration have
also been reported (Smith & Jewiss, 1966; Deinum
et al., 1968).
Temperature and digestibility
The IVTD and the IVCWD indicated a very high
quality of all forage samples (Tables VI and VII),
which is in good agreements with the low NDF and
ADF values observed. Within a given species, a low
Table III. Concentration of NDF, ADF and hemicellulose in seven grass species after three weeks at different temperatures in growth
chambers or a greenhouse.
NDF (g kg�1 DM) ADF (g kg�1 DM) Hemicellulose (g kg�1 DM)
TemperatureGrowth chamber
Greenhouse
Growth chamber
Greenhouse
Growth chamber
GreenhouseSpeciesz day/night (8C) 9/5 13/9 17/13 9/5 13/9 17/13 9/5 13/9 17/13
Meadow foxtail 318 381 427 481 172 195 223 249 146 186 204 233
Tufted hair grass 377 419 490 535 188 212 245 263 189 207 245 272
Meadow fescue 290 368 456 462 143 198 253 249 147 170 204 213
Red fescue 384 425 464 520 191 218 238 264 193 208 226 256
Perennial ryegrass 255 327 393 438 132 177 220 241 123 150 173 197
Timothy 316 392 472 503 184 244 301 324 132 148 172 179
Kentucky bluegrass 379 419 480 484 185 244 292 298 195 175 188 186
Average 331 390 455 489 171 212 253 270 161 178 202 219
SEM (n�/84, 56df)�/7.6 SEM (n�/84, 56df)�/5.9 SEM (n�/84, 56df)�/5.1
zSpecies and temperature effects, and their interaction, differed significantly (pB/0.001) for all fibre fractions.
Table IV. Concentration of NDF, ADF and hemicellulose in seven grass species sampled at four different dates in a greenhouse.
NDF (g kg�1 DM) ADF (g kg�1 DM) Hemicellulose (g kg�1 DM)
Speciesz Date 19 June 26 June 3 July 10 July 19 June 26 June 3 July 10 July 19 June 26 June 3 July 10 July
Meadow foxtail 400 490 494 481 201 254 261 249 199 237 233 233
Tufted hair-grass 435 535 220 263 215 272
Meadow fescue 388 446 458 462 187 225 238 249 201 221 219 213
Red fescue 414 450 468 520 192 212 226 264 222 238 242 256
Perennial ryegrass 372 448 432 438 192 229 236 241 180 219 196 197
Timothy 451 516 536 503 229 265 279 324 222 252 258 179
Kentucky bluegrass 438 501 510 484 217 251 262 298 222 250 249 186
Average 414 475 483 489 205 239 250 270 209 236 233 219
SEM (n�/21(18), 14(12) df) 5.7 6.1 8.8 7.5 7.8 4.6 5.3 5.9 6.4 3.9 5.6 3.6
zSpecies differed significantly (pB/0.001) for all fibres at all harvest dates.
Temperature effects in grasses 325
ADF concentration indicates a high IVTD value.
The average ADF concentration was lower than
270 g kg�1 DM (Table VI). In general, the IVTD is
about 100�130 g kg�1 DM higher than the in vitro
DM digestibility value, IVDMD (Tilley & Terry,
1963; van Soest et al., 1966; Goering & van Soest,
1970). Samples in our study consisted mostly of
leaves and results are in agreement with previously
reported IVTD values for leaves (Belanger &
McQueen, 1997, 1998 & 1999).
Table V. Daily increase in NDF, ADF and hemicellulose for each degree (8C) in temperature (218 are results from the greenhouse).
SpeciesTemperature
interval (8C)
NDF (g kg�1 DM d�1 8C�1) ADF (g kg�1 DM d�1 8C�1) Hemicellulose (g kg�1 DM d�1 8C�1)
9�13 13�17 17�21 9�13 13�17 17�21 9�13 13�17 17�21
Meadow foxtail 0.81 0.56 0.63 0.30 0.34 0.30 0.52 0.22 0.34
Tufted hair-grass 0.54 0.87 0.52 0.31 0.40 0.21 0.23 0.46 0.31
Meadow fescue 1.00 1.08 0.07 0.71 0.67 �/0.05 0.30 0.42 0.11
Red fescue 0.53 0.48 0.65 0.35 0.24 0.30 0.19 0.22 0.35
Perennial ryegrass 0.93 0.81 0.52 0.58 0.53 0.24 0.35 0.28 0.28
Timothy 1.00 1.00 0.36 0.77 0.70 0.28 0.21 0.29 0.08
Kentucky bluegrass 0.52 0.75 0.05 0.76 0.59 0.07 0.26 0.16 �/0.02
Average 0.76 0.79 0.40 0.54 0.50 0.19 0.29 0.29 0.21
SEM (n�/84, 56df)z�/0.128 SEM (n�/84, 56df)z�/0.099 SEM (n�/84, 56df)z�/0.086
zSEM for daily increase for each species and growth chamber.
Table VI. In vitro true digestibility (IVTD) and in vitro cell wall digestibility (IVCWD) for each species after three weeks at different
temperatures in growth chambers or a greenhouse.
IVTD (g kg�1 DM) IVCWD (g kg�1 NDF)
Growth chambers
Greenhouse
Growth chambers
GreenhouseSpeciesz Temperature day/night (8C) 9/5 13/9 17/13 9/5 13/9 17/13
Meadow foxtail 956 933 907 870 863 824 783 730
Tufted hair-grass 918 897 847 811 781 754 689 646
Meadow fescue 974 955 934 936 912 877 855 862
Red fescue 942 925 903 865 848 823 792 741
Perennial ryegrass 980 971 953 941 923 911 880 866
Timothy 958 944 914 877 868 856 817 755
Kentucky bluegrass 952 937 905 863 875 849 801 716
Average 954 937 909 880 867 842 802 759
SEM (n�/84, 56df)�/4.4 SEM (n�/84, 56df)�/8.7
zSpecies and temperatures differed significantly (pB/0.001) for both IVTD and IVCWD.
Table VII. In vitro true digestibility (IVTD) and in vitro cell wall digestibility (IVCWD) of grass species sampled at three different dates in
the greenhouse.
IVTD (g kg�1 DM) IVCWD (g kg�1 NDF)
Speciesz 26 June 3 July 10 July 26 June 3 July 10 July
Meadow foxtail 897 888 870 790 774 730
Tufted hair-grass 811 646
Meadow fescue 943 941 936 872 870 862
Red fescue 914 898 865 809 782 741
Perennial ryegrass 950 942 941 889 865 866
Timothy 923 898 877 850 810 755
Kentucky bluegrass 925 905 863 849 816 716
Average 925 912 892y 843 819 778y
SEM (n�/21 or 18, 14 or 12df) 5.4 3.7 5.1 10.7 7.3 8.6
zSpecies differed significantly (pB/0.001) for both IVTD and IVCWD at all dates.yDeschampsia caespitosa L. is not in the average because the first two harvest dates are missing.
326 G. Thorvaldsson et al.
Perennial ryegrass was consistently ranked highest
in digestibility followed by meadow fescue which
also correlates well with the fibre values. Tufted hair-
grass was always lowest in digestibility which agrees
with earlier findings (Olafsson, 1998). The decline in
digestibility over time was also slower for perennial
ryegrass and meadow fescue than for the other
species (Table VII).
Increasing temperature significantly decreased the
IVTD and IVCWD of all species (Table VI). The
temperature effect was lowest for perennial ryegrass
and highest for tufted hair-grass but similar for the
other species. On average, the decline in IVTD
increased by 0.22 g kg�1 DM day�1 (0.022 per
cent units) for each degree of increase in growth
temperature between 9 and 138C, and by
0.35 g kg�1 DM day�1 (0.035 per cent units)
between 13 and 178C (Table VIII). The average
temperature in the greenhouse was around 218Cwith more light and greater temperature fluctuations
than in the growth chambers. With awareness of the
limitations in comparisons, similar calculations were
made between the growth chamber at 178C and the
greenhouse. Between 17 and 218C, the coefficient
averaged 0.33 g kg�1 DM day�1 (0.033 per cent
units), similar to that for the temperature range of
13�178C. The temperature effects for the decline in
IVCWD (Table VIII) were a little higher than for the
IVTD, as expected.
Coefficients for effects of temperature on digest-
ibility in timothy have been calculated in several
outdoor experiments (which shows the effects of
each degree change in temperature on decline in
digestibility); the average value was 0.059/0.01 per
cent units 8C�1 (Thorvaldsson, 1987; Thorvaldsson
& Fagerberg, 1988; Thorvaldsson & Bjornsson,
1990; Thorvaldsson et al., 2000), which is a little
higher than the average value determined in the
present experiment. This difference in temperature
effect may be explained, in part, by the fact that the
plants in the current experiment remained in the leaf
stage whereas in the outdoor experiments the plants
were more mature at first sampling date and harvest
continued after heading. In a growth chamber
experiment in Sweden the coefficients for timothy
were also found to be a little higher than in the
present study (Thorvaldsson, 1992).
Deinum et al. (1968) calculated a coefficient for
temperature effects on digestibility of perennial
ryegrass based on data from an outdoor experiment
and found 0.57 digestibility units during a period of
four weeks, or 0.02 units for each day, which is
similar to our results.
Conclusions
For all species tested in this study, increased
temperature decreased digestibility and increased
fibre content. The extent of the temperature effects
varied among species. Changes in digestibility and
fibre over time were also species-dependent. These
estimated parameters will be useful for simulation
and modelling studies of changes in digestibility and
fibre content for temperate grasses.
Acknowledgements
The experiment was performed at the Nova Scotia
Agricultural College in Truro, NS, Canada. Our
thanks are expressed to the College and the staff of
the Department of Plant and Animal Sciences and
the Department of Environmental Sciences for their
help and support.
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