Abomasum

Abstract: Three experiments were conducted to determine the fate of condensed tannins (CT) during digestion in sheep. CT were measured as extractable, protein-bound and fibre-bound fractions using the butanol-HCl procedure. In Expt 1, purified CT were added to digesta from different parts of the digestive tract obtained from a pasture-fed sheep. Recoveries of CT after 0 and 4 h of anaerobic incubation at 39 degrees averaged: rumen 78.9 and 57.5%; abomasum 50.9 and 49.0%; duodenum 64.4 and 46.0% and ileum 43.4 and 38.8%. In Expt 2, [14C]CT was given per abomasum over a 6.5 h period at 15 min intervals to a sheep previously fed on Lotus pedunculatus (which contains CT). The sheep was killed at the end of the period and 92.4% of the label was recovered. Virtually all of the label was in the digesta, and none was detected in the blood, so that the CT-carbon appeared not to be absorbed from the small intestine. In Expt 3, rumen, abomasal and ileal digesta and faeces samples from sheep fed on Lotus pedunculatus were analysed for CT and CT flow along the digestive tract calculated from reference to indigestible markers. Values were low in all digesta samples, indicating disappearance of CT across the rumen and small intestine, and CT recovery in faeces was only about 15% of intake. However, the 14C results from Expt 2 suggested that little if any CT-carbon was absorbed and the low recoveries in Expt 1 are considered to be a consequence of either conformational changes to the CT molecule such that it is no longer detectable by colorimetric methods, an inability of the analytical method to release bound CT for the butanol-HCl assay, or interference from other digesta constituents. It is concluded that the butanol-HCl method of CT analysis is appropriate for quantifying CT in herbages but not in digesta or faeces, and that a substantial part of CT released during protein digestion in the small intestine may not be detectable by normal CT analytical methods.

Abstract: Direct measurement has been made of the daily production of microbial protein in the rumen. When sheep were fed on a virtually protein-free purified diet, increases in the intake of nitrogen from 2 to 9 g/day increased linearly the production of protein in the rumen from 32.5 to 50.0 g/day. There was no further increase in protein production when the nitrogen intake was raised to 16 g/day. The amount of total nitrogen flowing out of the rumen showed a net increase over that ingested at daily nitrogen intakes of 2 and 4 g, no change at 9 g, and a substantial net loss at 16 g. At the lowest nitrogen intake at least 4 g recycled nitrogen was utilized by the rumen microorganisms daily. The yield of protein from the ruminal fermentation increased from 9.1 g/100 g organic matter digested in the rumen when nitrogen was most limiting, to 13.3 g/100 g when nitrogen was in excess of requirements. It was calculated that protein production in the rumen at the highest nitrogen intake was less than the potential production from the energy supplied to the microorganisms. Possible limiting factors are discussed.