The effect of varying the amount of linseed oil supplementation on rumen metabolism in sheep

The effects of three levels of linseed oil (LSO) supplementation of a basal diet on rumen digestion and flow of nutrients to the proximal duodenum of three mature sheep provided with permanent rumen and duodenal re-entrant cannulas were studied. 2. A basal diet of 200 g hay and 400 g concentrates daily, providing approximately 7.0 MJ digestible energy and 13 g N/d, was given alone or with supplements of 13, 26, or 40 ml LSO/d in two equal portions of 06.00 and 18.00 hours. The flow of duodenal digesta was measured by spot-sampling using chromic oxide paper as the marker. Bacterial protein synthesis (BPS) was measured by the diaminopimelic acid technique. 3. Addition of LSO reduced the digestion of energy and organic matter, particularly acid-detergent fibre, in the stomach. Digestion in the intestines increased but at the higher levels of supplementation this failed to compensate completely for the reduction in rumen digestion. Total volatile fatty acid concentrations were not affected but molar proportions of acetate and butyrate were decreased by approximately 18 and 61% respectively while the molar proportion of propionate was increased twofold by the highest concentration of oil. The higher concentrations of LSO virtually eliminated protozoa from the rumen. 4. The second increment of LSO (26 ml/d) produced the highest duodenal flow of total N and bacterial N and the highest efficiency of BPS. The highest concentration of oil (40 ml/d) was without effect. Rumen and duodenal ammonia concentrations and plasma urea concentrations tended to be reduced by the higher concentrations of LSO. 5. It is argued that the results support suggestions made elsewhere that free oils reduce the efficiency of BPS but that they also reduce the numbers of protozoa which can cause an increase in efficiency of BPS. The net effect of free oil supplementation on BPS is thus likely to be variable and difficult to predict.     

Involvement of the solid phase of rumen digesta in the interaction between copper, molybdenum and sulphur in sheep

1. Merino sheep fed on a diet of chopped wheaten hay, chopped lucerne (Medicago sativa) hay and oat grain were the source of rumen contents for the study. The diet contained (mg/kg dry weight) 3.3 copper, 0.24 molybdenum and 2.8 sulphur. The effects of adding between 5 and 25 mg Mo/kg as ammonium molybdate (AM) or tetrathiomolybdate (TTM) on the distribution and forms of Cu and Mo in rumen contents were investigated in vivo and in vitro. 2. Approximately 88% of the Cu and 94% of the Mo in rumen contents were associated with the solid phase. When AM or TTM was added to rumen contents in vivo or in vitro the proportion of these elements in the solid phase was increased at the expense of the fluid phase. 3. The addition of AM and TTM to rumen contents also decreased the proportion of Cu that was soluble in trichloroacetic acid (50 g/l; TCA) and increased the proportion of Cu that was not extractable by sequential treatment with TCA and neutral detergent. 4. Column chromatography of neutral-detergent extracts of rumen contents revealed that TTM treatment caused Cu to be strongly bound to proteins of high molecular weight. 5. Addition of sulphide to rumen contents did not result in significant changes in the distribution of Cu between the fluid and solid phases, or in the solubility of Cu in TCA. 6. It is postulated that constant removal of TTM from the fluid phase via reaction with proteins and other macromolecules in the solid phase results in greater formation of TTM in vivo than would be expected from solution chemistry. The molybdo-proteins so formed are strong chelators of Cu and may be the agents responsible for the decrease in Cu absorption in animals that consume diets containing high concentrations of Mo.     

Factors affecting the voluntary intake of food by sheep. 5. The inhibitory effect of hypertonicity in the rumen

The site where osmotically active substances act to depress food intake was determined in sheep. After 5.5 h of food deprivation, solutions of sodium chloride or polyethylene glycol-200 (PEG-200) were added to either the reticulo-rumen or the abomasum. The sheep were then immediately offered pelleted lucerne (Medicago sativa). Water was withheld during the first 60 min of feeding but was available from 60 to 90 min. There was a linear inhibition in food intake in the first 10 min after loading 2.37, 6.25, 12.5, 25.0 or 50.0 g NaCl into the rumen according to a 5 x 5 Latin square design (P = 0.0001). The intake reduction was 3.49 g food/g NaCl. An osmotic load of PEG-200 equivalent to 50 g NaCl also significantly inhibited food intake in the first 10 min of the meal compared with a control treatment. The inhibition of food intake after loading 55 g NaCl into the rumen was not affected by injecting lidocaine hydrochloride into the reticulum immediately before NaCl loading. NaCl injected into the abomasum did not significantly affect food intake in the first 10 min of feeding even though the tonicity of abomasal digesta was increased to unphysiological levels. There was no consistent relationship between food intake and the change in the tonicity of jugular plasma following solute loading and drinking. The sensing site of hypertonicity was localized to the wall of the reticulo-rumen where neuronal receptors appear to be capable of detecting osmotic pressure within the physiological range to depress food intake. These receptors should be identified and characterized because of their possible significance in limiting food intake by ruminants.     

The effect of increasing methionine supply on the methionine conversion to cyst(e)ine in sheep

The conversion of methionine to cyst(e)ine was determined in sheep infused with different amounts of methionine (0-5 g/d) into the duodenum by assaying the incorporation of 35S from intravenously-infused L-[35S]methionine into cyst(e)ine in wool, plasma albumin and the free plasma pool. The percentage of cystine-S in the plasma originating from methionine increased linearly from 4.5 to 18 with increasing supplemental methionine supply. The percentage of cysteine-S in albumin increased from 15 to 50; methionine supply increased to 3 g/d but then remained constant, indicating that the transsulphuration pathway of the liver was exceeded. The percentage of wool cysteine-S originating from methionine was high (approximately 70) at all methionine supplementation rates.     

Urease (EC 3.5.1.5) inhibition in the sheep rumen and its effect on urea and nitrogen metabolism.

The urease (EC 3.5.1.5) inhibitor, phenylphosphoryldiamidate (PPDA), was given by continuous infusion into the rumen of two sheep nourished by intragastric infusion and into either the rumen or abomasum of four sheep given a pelleted diet containing 119 g crude protein (nitrogen x 6.25)/kg dry matter. PPDA was given at 1 g/d in infusion sheep and 1.5 g/d in the normally-fed sheep. Measurements of urea kinetics were made using single injections of [14C]urea. Urease inhibition was complete within 24 h of starting PPDA infusions to the rumen; in this time-period, urea concentration in rumen contents reached equilibrium with that in plasma and this situation persisted until infusions were terminated. Relative to the control periods, plasma urea and rumen ammonia concentrations were unchanged but urea irreversible loss rate decreased by 26% in infusion sheep and 33% in fed sheep when PPDA was given. Urinary urea excretion was not affected, hence urea degradation, measured by difference, decreased by 77 and 58% respectively in response to urease inhibition. Administration of PPDA to the abomasum resulted in a reduction in rumen urease activity to about 40% of control values but had no effect on urea metabolism. Differences between treatments in daily nitrogen retention were not significant, indicating that under the dietary conditions imposed in these experiments, even substantial changes in urea recycling had only minor effects on the overall N economy of the animal.     

Some effects of sulphur intake on molybdenum metabolism in sheep.

1. To investigate the effects of sulphur intake on molybdenum metabolism in sheep, ewes were given intakes of 0.3 or 3.5 mg Mo and 0.98, 1.33, 1.73 or 3.23 g S/d in a 2x4 factorial experiment with two replicates lasting 35 d. 99Mo with 0.1 mg carrier Mo was infused intravenously for the last 14 d and, when 99Mo concentrations in urine and faeces had attained plateaux (days 11-14), stable Mo and 99Mo balance trails were conducted; samples of blood and rumen contents were taken principally for studies of Mo distribution. 2. Increases in S intake caused the following changes in Mo metabolism; absorption decreased, urinary and faecal endogenous excretion decreased and retention increased; Mo concentrations in rumen contents decreased but the predominant association with the solid phase was unaffected; Mo concentrations in plasma decreased, but a higher proportion was associated with the protein fraction; Mo in protein-free plasma became apparently less ultrafiltrable at the glomerulus. 3. The pattern of response to S for each factor was generally curvilinear, the first increment in S intake having by far the greatest effect. The effect of S was generally greatest at the higher Mo intake. 4. It is suggested that the manifold effects of S on Mo metabolism are related to a common interaction in the rumen leading to the formation of Mo-complexes, possibly thiomolybdates, which are poorly absorbed but even more poorly excreted.     

Initial studies on leucine metabolism in the rumen of sheep

1. [3H]leucine infused directly into the rumen of sheep labelled microbial protein and, when compared with the specific activity of the rumen free-leucine pool, indicated that 50% of the bacterial protein leucine originated from the rumen free-leucine pool. 2. The lower limit for bacterial protein turnover in the rumen was 0.37/d when calculated as the difference between the specific rate of disappearances of labelled bacteria from the rumen and the liquid-phase dilution rate. 3. Intravenously infused leucine also labelled the rumen bacteria. The build-up of specific activity in the rumen bacteria was sigmoidal and did not resemble that of the salivary protein which suggested that the rumen epithelium was a major endogenous protein input to the rumen. Additionally, bacteria isolated from the rumen epithelium had high radioactivity indicating that they were ingesting the rumen epithelial cells.     

The effect of partially replacing urea nitrogen with protein N on N capture in the rumen of sheep fed a purified diet.

1. The influence of replacing 10% of the urea nitrogen in a purified diet with casein, maize gluten or white fish meal on the efficiency of conversion of dietary-N into microbial N was examined using sheep equipped with rumen fistulas and duodenal re-entrant cannulas. 2. Total nitrogen (TN), non-ammonia nitrogen (NAN) and amino acid nitrogen (AAN) flowing to the proximal duodenum were significantly higher (P smaller than 0.05) when maize gluten was added to the diet, and this appeared to be due to an increased efficiency of microbial protein production. 3. Pepsin secretion was not significantly different between treatments and the daily amount of pepsin N flowing to the proximal duodenum was very small (40-53 mg). The peak of pepsin activity in duodenal digesta was reached 6-8 h after feeding. 4. The possible practical implications of the results are discussed.