APPARENT DIGESTIBILTY OF AMINO ACIDS AND OTHER NITROGENOUS COMPOUNDS IN THE SMALL INTESTINE OF WETHERS EXPOSED TO A COLD ENVIRONMENT
Digestion studies were conducted with eight shorn yearling Suffolk wethers to assess the effects of environmental temperature on intestinal digestion of nonammonia nitrogen (NAN) and amino acid N. The wethers were cannulated in the rumen, abomasum, and terminal ileum and subsequently chronically exposed to either cold (0–2 °C) or warm (21–25 °C) temperatures in a crossover experiment. Sheep were fed a diet of chopped bromegrass hay and digesta flows through the abomasum and terminal ileum were estimated by reference to 103ruthenium-phenanthroline and 51chromium-EDTA. Microbial N contributions to total N in abomasal digesta were estimated with 35sulphur. During cold exposure, mean rumen ammonia concentration was reduced (P < 0.01) by 20%, while net appearance of NAN across the forestomach increased from 2.7 to 7.3 g d−1 (P < 0.05) resulting in a 14% increase in flow of NAN from the abomasum. The latter was associated with a 63% increase in flow of undegraded feed N (P < 0.05) and a nonsignificant decrease in microbial NAN. There was a small increase in flow of most amino acids from the abomasum due to cold exposure, with significant effects for lysine, histidine and tyrosine (P < 0.05). Disappearances of lysine (P < 0.05) and tyrosine (P < 0.005) in the small intestine were increased by the cold environment. Cold exposure increased small intestinal digestion of amino acid N relative to digestible organic matter intake (P < 0.08) suggesting maintenance of amino acid supply relative to that of energy in a cold environment. Key words: Amino acids, digestion, small intestine, sheep, cold environment