Changes in ruminal and intestinal digestion during and after weaning in dairy calves fed concentrate diets containing pea or soya bean meal. 2. Amino acid composition and flow of duodenal and heal digesta, and blood levels of free amino acids

Abstract

Changes in the amino acid (AA) contents of duodenal and ileal digesta, and levels of plasma free AA were studied in dairy calves progressively weaned on high-concentrate diets differing in the protein source (pea vs. soya bean meal). Digesta flowing from the stomachs of calves presented a fairly constant AA composition by 2–3 weeks after the commencement of dry feed intake. Protein in the duodenal digesta was mainly microbial. Ileal digests from ruminating calves presented an AA composition very different from that of milk-fed calf digesta. The latter contained mostly endogenous protein while bacterial protein was the main constituent of the former. Ileal AA composition and the composition of apparently absorbed AA were not affected by age after weaning. Changes in plasma free AA patterns through weaning were dominated by a decrease in several AA levels (methionine, lysine and arginine) which could be related to changes in metabolizable energy intake and amounts of AA apparently absorbed in the small intestine. AA profiles of duodenal and ileal digests, and of plasma were never greatly affected by the origin of protein in solid feeds used in this trial.