NITROGEN TRANSFORMATIONS AND DUODENAL AMINO ACID CONTENT IN SHEEP GIVEN FOUR FORAGE DIETS AND EXPOSED TO WARM AND COLD AMBIENT TEMPERATURES

Abstract

Sixteen closely-shorn sheep fistulated at the rumen and duodenum were exposed to temperatures of 22–25 °C or 1–4 °C for periods of 45 d. Comparisons were made of digestion of nitrogen from alfalfa, red clover, reed canarygrass and bromegrass diets given in the chopped, or ground and pelleted form at intervals of 2 h. There was no consistent effect of environmental temperature on flow of nonammonia N to the intestines, irreversible loss rate of rumen ammonia, or rate of digestion of dietary N from nylon bags. In addition, apparent N digestibility in the gastrointestinal tract was not affected by environmental temperature, but cold exposure resulted in increases (P < 0.05) in apparent digestion of nonammonia N in the intestines relative to total intake of digestible organic matter. Grinding and pelleting of diets decreased (P < 0.001) rumen ammonia concentrations and increased (P < 0.01) total amino acid content of duodenal nonammonia N. There were dietary differences in flows of duodenal N, rumen ammonia concentration and rates of digestion from nylon bags. It was concluded that there were interactions between diet, dietary form, and the ratio of nitrogenous to energy-yielding metabolites which determine responses of ruminants to cold exposure. Key words: Cold stress, nitrogen, amino acids, sheep