The digestion by cattle of silage-containing diets fed at two dry matter intakes. 2. Digestion of total amino acids and of D-alanine and D-glutamic acid.

In a 4 X 4 Latin square experiment four cows were given, twice daily, diets consisting of (g/kg dry matter (DM)) 500 barley, 400 grass silage and 100 soya-bean meal. The diets were given at either 1.15 (L) or 2.3 (H) times maintenance energy requirements and the soya-bean meal was either untreated (U) or formaldehyde (HCHO)-treated (T). The passage of digesta to the duodenum was estimated using chromic oxide as a flow marker; 35S was used to estimate the amount of microbial protein entering the small intestine. A microbial fraction was prepared by differential centrifugation from duodenal digesta. Samples of bacteria and of protozoa from rumen digesta were also prepared. The total amino acid contents of feedingstuffs, duodenal digesta, duodenal microbial material, rumen bacteria and rumen protozoa were determined by ion-exchange chromatography. The D-alanine and D-glutamic acid contents of the samples were determined by gas-liquid chromatography. The quantity of each amino acid entering the small intestine was significantly (P less than 0.001) increased by increasing DM intake and tended to be increased by formaldehyde-treatment of the soya-bean meal. There were net losses of all amino acids across the forestomachs except for lysine, methione, D-alanine and D-glutamic acid for which there were net gains. There were significant (P less than 0.05) differences in amino acid composition between rumen bacteria and duodenal microbial material; differences in amino acid composition between rumen bacteria and rumen protozoa were also observed.(ABSTRACT TRUNCATED AT 250 WORDS)