Effect of dietary dry matter intake on endogenous nitrogen flows in growing lambs

Summary The effect of dietary dry matter intake ( DMI ) on endogenous nitrogen (N) flows at different part of the digestive tract of growing lambs was determined using a 15 N isotope dilution technique. Three Kazakh male lambs (30 ± 2.75 kg of body weights and 4 months old, average daily gain 200 g/day) were fitted with ruminal, duodenal and ileal cannulae and raised in metabolic cage individually. The experiment was conducted in a 3 × 3 Latin square design with three lambs, three DMI levels (1100, 920 and 736 g/day respectively) and three periods. Each period lasted 18 days, consisting of 10 days for adaptation, 8 days for the continuous infusion of l ‐[ 15 N]leucine, during which the intestinal flow of N and 15 N enrichment were determined. The total endogenous secretions in the forestomach ( S fs ) were decreased (p = 0.0512) with increased level of DMI . On the contrary, endogenous nitrogen ( EN ) secretions into the small intestine ( S i ) increased (p = 0.0249) significantly with the high level of DMI ( HI ) group compared with that of low level of DMI ( LI ). Total absorption from forestomach was reduced (p = 0.0121) with increased level of DMI , whereas total absorption from small intestine for HI group increased (p = 0.0116) significantly compared with that of LI treatment. The real digestibility of N in the rumen accompanied with the increase in feed intake is decreased (p = 0.081). In contrast, there were no effects of DMI level on the computed real digestibility of N across both small intestine and whole tract. The results of this study indicate that the total flows of EN at duodenum may be unaffected by the level of DMI ; however, the EN flow at ileal level increased from 12% to 37% with the increase in DMI level, corresponding to 33% of total N flow at ileum.