J. Sci. Food Agric. 1982,33, 1057-1062

The Effects upon Digestion in Sheep of the Dietary Inclusion of Additional Salivary Salts

M. Hadjipanayiotoua, D. G. Harrison and D. G. Armetrong

Department of Agricultural Biochemistry and Nutrition, University of Newcastle upon Tyne, Newcastle NEI 7RU

(Manuscript received 6 January 1982)

Four mature Suffolk x halfbred wether sheep, fitt’ed with rumen fistula and re-entrant cannulae at the proximal duodenum and terminal ileum were given in sequence, a control diet (diet 1) and that diet supplemented with either 20 or 40 g saliva salt kg-1 (diets 2 and 3 respectively). The addition of 20 g salt kg-l failed to alter significantly the rumen fermentation pattern and dilution rate. In contrast, the feeding of diet 3 resulted in a significant increase in the molar proportions of ruminal acetate, a non-significant decrease in propionate and a significantly higher rumen dilution rate (D), which was positively correlated with the molar proportions of acetate. Ruminal NHs-N concentration tended to increase with salt supplementation, with the greatest concentration being observed at the highest level of salt inclusion. The presence of the salts significantly reduced the degradability of the feed protein within the reticulo- rumen. The dietary inclusion of the salts resulted in a non-significant increase in total amino acid N (TAA-N) and a significant increase in the organic matter entering the small intestine.

1. Introduction

The microorganisms present in the rumen degrade the structural carbohydrate of the feed to simple sugars which are in turn fermented to volatile fatty acids (VFA), methane, lactic acid and carbon dioxide.1 The VFA are mainly acetic, propionic and butyric acids and their relative molar propor- tions in the rumen liquor (the fermentation pattern) are influenced by diet,z level of intake,3 rumen P H , ~ and rumen dilution rate.5 The rumen fermentation pattern may affect rumen microbial protein synthesis; Ishaque rt a1.6 showed that the efficiency of protein synthesis was decreased with increasing ruminal acetate but Chamberlain et aL7 in contrast, concluded that protein synthesis is not always correlated with the molar proportion of propionic acid and that where correlations occur, they can be positive or negative.5~ *

Earlier work5 showed that the addition of 40 g kg-l ‘saliva salt’ to a diet of 60 % ground maize and 40% dried grass markedly increased the proportions of acetate in the rumen of sheep,5 and that this change in fermentation pattern was associated with an increased rumen dilution rate (D).5.9 This work was extended to the dairy cowlo where the dietary addition of saliva salt in animals fed high-concentrate diets markedly increased ruminal acetate proportions and prevented the ‘low milk fat’ syndrome often associated with such diets. In view of the potential nutritional significance of the above findings, it seemed appropriate to examine, using cannulated sheep, the effects of the dietary inclusion of ‘saliva salt’ upon D, fermentation pattern, microbial protein synthesis and the sites of digestion of N, organic matter and amino acid N.

Present address: Agricultural Research Institute, Nicosia, Cyprus. Present address: School of Veterinary Medicine, University of Yucatan, Merida, Mexico.

0022-5142/82/1100-1057 $02.00 0 1982 Society of Chemical Industry

68 1057

1058 M. Hadjipanayiotou et ul.

2. Experimental

2.1. Animal management and sample collection Four mature Suffolk x halfbred wether sheep, weighing approximately 40-50 kg were used as experimental animals. In a single operation each sheep was fitted with a rumen fistula and re-entrant cannulae at the proximal duodenum and terminal ileum.11 The animals were housed in metabolism crates in a controlled environment (15 +2"C) with continuous lighting during the measurement periods.

2.1.1. Diets The control diet (diet 1) contained (g kg-l): barley 466; dried grass 466; soya bean meal 19; molasses 19; mineral-vitamin mix 30 and sufficient chromic oxide to provide each animal with c 4 g CrzOs/day. The mineral-vitamin mix contained (g kg-1): FeSO4, 5.0; CoS04, 0.08; ZnO, 2.11; MnS04, 4.6; Ca(IOs)z, 0.05; NaCl, 167; CaHP04, 370; molasses, 20; cereal base, 430; vitamin A (i.u. kg-I), 5 x lo6; vitamin D (i.u. kg-I), 1 x lo6. All dietary components were finely ground. Diets 2 and 3 were prepared by adding 'saliva salt' to the control ration at the levels of 20 and 40 g kg-l respectively and the three diets were pelleted through a 9 mm die. All animals received their daily feed allowance (1 kg of the appropriate diet plus 50 g of hay) in two equal portions at 08.00 and 16.00 hours. Feed intakes were recorded daily. The animals were maintained on the appropriate diet for at least 14 days prior to the collection of any samples and were given the control diet first, followed by diets 2 and 3.

2.1.2. Compostion of saliva salt The salt contained (g kg-1): NaHC03 725; NaHzP04, 254; NaCI, 13; KCl, 8.

2.2. Collection of samples Small samples (c 100 ml) of rumen liquor were taken every third day during the experimental periods which each lasted at least 24 days. After pH measurement 10 ml of the liquor was mixed with an equal volume of O.~N-HC~ and the sample retained for the measurement of ammonia-N (NH3-N). 4 ml of the rumen liquor was also mixed with 1 ml of deproteinising solution ( 1 ~ crotonic acid in 2.5 M metaphosphoric acid) and the sample retained for VFA analysis. All samples were stored at - 20°C until required.

Duodenal and ileal digesta were collected over a period of 24 h according to the modified method of MacRae and Armstrong,l2Sl3 and the quantities of feed and microbial protein entering the duodenum were determined by the method of Elliott and Arm~tr0ng. l~

2.3. Chemical methods All samples of duodenal and ileal digesta were analysed for Crz03 content15 and the values used to correct the daily flow of digesta for 100% recovery of C r ~ 0 3 . l ~ Samples of freeze-dried digesta and feed were analysed for individual and total amino acid nitrogen.l6 Dry matter (DM) was determined by drying in an oven at 105°C for 24 h and ash content by heating at 550°C for a further 24 h. The concentration of total VFA and the relative proportions of the individual VFA in rumen liquor were determined using a Pye 104 gas-liquid chromatograph,l6 and rumen dilution rate (D) was determined using Cr-EDTA.l7 Ruminal NH3-N concentration was determined by steam distillation of the rumen liquor and total-N by the macro-Kjeldahl procedure.

2.4. Statistical analysis Analysis of variance was conducted on the results and the animal and treatment effects were isolated. Despite the fact that periods and treatments were totally confounded, previous experience5 has shown that the effects on mature wether sheep over time are very small; consequently all treatment/ period effects are assumed to be the results of the imposed treatments only.

Effects upon digestion in sheep 1059

3. Results

Table 1 shows the mean values for the rumen VFA, pH and NH3-N. There were no significant differences in VFA concentration between diets. The feeding of diet 3, however, resulted in a significant increase (P< 0.05) in the molar proportion of acetate and a non-significant decrease in the proportion of propionate. There were no significant differences between diets with respect to the proportions of butyrate, isobutyrate and valerate. Rumen NH3-N was significantly (P< 0.05) higher with diet 3, and the rumen pH with diet 2 was significantly higher (P<O.O5) than with diet 1. The rumen dilution rate obtained with diet 3 was significantly higher (P<O.O5) than the D values obtained with the other two diets.

The values for flow of organic matter (OM) and for the proportionate disappearance of digested OM in the different sections of the digestive tract are shown in Table 2. The dietary addition of the

Table 1. Mean valuesa for the total concentration and molar proportions of rumen VFA, and for rumen pH, NH3-N concentration and dilution rate of four sheep fed the three diets

Diet

1 2 3 s.e.b

VFA concentration (mmol litre-l) Molar proportions of

Acetate Propionate Butyrate Isobutyrate Valerate

Rumen pH Rumen NHI-N (mg litre-1) Rumen dilution rate h-l

101

0.572u 0.283 0.119 0.012 0.014 6.01a

0.053" 165"

103

0.594'8 0.255 0.125 0.010 0.016 6.43b

0.059" 177a

95

0.639b 0.219 0.120 0,010 0.012 6.19"b

0.077b 234b

6.46

0.0168 0.0286 0.0167 0.0001 0.0002 0.109

0.0069 18.7

a Means on the same line having different superscripts are significantly different (P<O.O5). Standard error of difference between two treatment means.

Table 2. The mean quantities" and digestibility of the organic matter passing through various sections of the gut

Organic matter (g day-') In feed At proximal duodenum At terminal ileum In faeces

Apparent digestibility of OM Proportionate disappearance of apparently digestible OM

Before the small intestine In the small intestine In the caecum and colon

Diets

1 2 3 s.e.b

809 367a 253 170

0.790

0.6921 0.178 0.129

795 389b 278 160

0.799

0.6452 0.171 0 . 1 8 3

785 3906 284 158

0.799

0.6292 0.170 0.202

3 .O 7 . 3

18.2 5 . 4 0.0069

0.0133 0.0303 0.0276

Means on the same line having different superscripts are significantly different (P < 0.05) and

Standard error of the differences between two treatment means. ineans having different subscripts are different ( P i 0.01).

1060 M. Hadjipanayiotou et al.

Table 3. The mean quantitiesa and digestibility of the N passing through the various sections of the gut

Diet

1 2 3 s.e.b

N (g day-9 In feed At proximal duodenum At terminal ileum In faeces In urine

Apparent digestibility of N N apparently absorbed (g day-1) Apparent digestibility of N in

small intestine

23.25 22.83 9.52 6.18 11.01 0.736 17.07”

0.584

24.76 24.45 10.92 6.23 10.38 0.748 18.53a

0.553

22.36 22.28 1.639 11.12 0.934 5.85 0.528 10.70 1.936 0.737 0.0183 16.52” 0.528

0.491 0.0520

a Means on the same line having different superscripts are significantly different (P<O.O5). Standard error of the difference between two treatment means.

‘salt’ significantly increased (P< 0.05) the duodenal flow of OM and significantly (P< 0.01) depressed the values for the proportionate disappearance of OM prior to the small intestine. The salt inclusion had no apparent effect upon the overall apparent digestibility of OM.

The addition of salt had no significant effect upon the quantities of N either entering the small intestine, leaving the small intestine or voided in the faeces (Table 3). The animals fed diet 2 absorbed significantly (P<O.O5) more N than those fed the other diets. The salt addition also had no significant effect upon the flow of total amino acid N (TAA-N) entering or leaving the small intestine (Table 4) or upon the apparent digestibility of TAA-N in the small intestine. The quantities of feed amino acid N (FAA-N) entering the small intestine were markedly and significantly (P< 0.05) increased by both levels of salt inclusion. The duodenal flow of microbial amino acid N ( M U - N ) was significantly (P<O.O5) reduced with diet 3. The salt additions had no significant effect upon the efficiency of synthesis of microbial N within the stomachs.

Table 4. Valuesa for the flow of total, microbial and feed amino acid N through the small intestine

Diets

TAA-N (g day-1) In feed At proximal duodenum At terminal ileum

in the small intestine

Microbial AA-N Feed AA-N Microbial-N

g kg-1 OM apparently digested

g kg-1 O M truly digested in

Apparent digestibility of TAA-N

Duodenal flow (g day-l) of

Microbial-N synthesised

in the rumen

the rumen

17.91 17.13 7.43

0.56

12.8OU 4.33n 16.32“

36.9

27.2

18.46 20.28 7.52

0.63

12.31“ 7.97’’ 15.020’1

36.1

26.6

16.99 17.89 7.45

0.586

9.41’’ 8.4gb 12.49’’

31.9

24.2

- 1.822 1.026

0.0413

1.372 1.350 1.405

2.85

1.60

a Means on the same line having different superscripts are significantly different (P< 0.05). Standard error of the difference between two treatment means.

Effects upon digestion in sheep 1061

4. Discussion

In this experiment the dietary inclusion of artificial saliva at 40 g kg-l induced a significant increase in the molar proportions of ruminal acetate, but had no effect upon total VFA concentration. This finding is in good agreement with previous work.589 The increase in acetate proportion was not, however, associated with an increase in the molar proportion of butyrate. This latter finding is in contrast to the data of Harrison5 and Perez-Lanzacls and may reflect differences in diet. When the salt additive was fed at 20 g kg-1 there was an increase in molar proportion of acetate which was not, however, statistically significant. The changes in fermentation pattern obtained with higher levels of salt supplementation9 are known to be associated with marked changes in the rumen bacte- rial population and it is possible that the inclusion of 20 g salt kg-l was insufficient to generate the required changes in the rumen microflora. The lack of significant response to the low level of salt addition was also partially due to the extremely low molar proportion of propionate found in one animal when fed the basal diet without addition of salt.

The increase in acetate molar proportion (Ac) obtained in this present experiment was positively correlated with an increase in rumen dilution rate and is in good agreement with previous work:5

Ac=0.511+1.403D, r=0.73, n=12

This increase in D was not associated with an increased efficiency of microbial protein synthesis and is contrary to the data of Harrison5 and in accord with the findings of Meggison.19 These differences may be due to differences in the pattern of feeding, as the increases in microbial growth efficiency obtained by Harrison et aL5 were obtained with animals fed on an hourly basis. In contrast, Meggisonlg and the present authors fed their animals twice daily; it might well be that the sudden addition of a large quantity of saliva salt to the rumen may elevate the ionic strength and osmolarity of the rumen fluid and thus might impair microbial protein synthesis.

The dietary addition of salt at both levels induced a significant increase in the duodenal flow of OM, Similar findings have been obtained previously and attributed to the increased feed and a-linked glucose escaping degradation in the rumen as a result of the increased dilution rate.5 However, Kellaway et ~1.20 fed a sodium bicarbonate supplement to calves and found an increased duodenal flow of ci-linked glucose even when D was not increased, and so it would seem likely that the increases in starch entering the small intestine obtained with salt feeding may be due to changes in microbial composition accompanying alterations in the rumen microflora. The addition of artificial saliva to the control diet resulted in a non-significant increase of TAA-N passing into the small intestine ( c 11 %). Much higher (c 32 %) values have been reported previously.5 However, in contrast to these previous data5 and in agreement with those of Meggison19 the increase in the present study was associated with significantly higher quantities of dietary rather than microbial AA-N entering the duodenum. The values for net disappearances of TAA-N within the small intestine obtained in this work (mean value 0.59) are relatively low compared with values previously reported.21922

In conclusion, it would seem that the dietary inclusion of saliva salt, as well as inducing an acetate fermentation pattern, could reduce the degradation of feed protein within the rumen and enhance the flow of total amino acids into the duodenum. A possible increase in the duodenal flow of a-linked glucose could be another benefit and the combination of these two factors may be the cause of the increased efficiency of milk production obtained when feeding saliva salts to dairy cattle.1°

The authors would like to record their thanks to Mr G. F. Brown, MRCVS, for veterinary super- vision of the sheep, and Messrs B. Brown and D. Smith for technical assistance.

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