Digestion of feed amino acids in the rumen and small intestine of dairy cows measured with nylon-bag techniques

Abstract

The disappearance of total N, non-protein-N and amino acid-N after washing, rumen incubation and intestinal passage of sugarbeet pulp, maize-gluten feed, maize feed meal, palm kernel meal, soyabean hulls, soyabean meal, grass silage, maize silage and concentrate was measured in four dairy cows using nylon-bag techniques. Disappearance of amino acid-N after washing varied between feedstuffs from 14 to 69% of feed amino acid-N, and was lower than disappearance of non-protein-N. For sugarbeet pulp, grass silage and maize silage, washing had a considerable effect on the amino acid profile. Disappearance of amino acid-N after rumen incubation was also lower than non-protein-N and varied between feedstuffs from 25 to 73% of feed amino acid-N. Rumen incubation had only a small effect on the amino acid profile of the residue after washing. Disappearance of amino acid-N in the intestine varied between feedstuffs from 70 to 99% of rumen undegraded amino acid-N, and was higher than the disappearance of non-protein-N. Intestinal incubation showed a considerable effect on the amino acid profile for all feedstuffs. It was concluded that protein that was assumed to escape rumen degradation and was absorbable in the intestine was higher in amino acids and methionine, and lower in non-amino acid-N and glutamic acid and proline compared with protein in the feedstuff.