Effect of feed intake on metabolizable protein supply in Dorper x thin-tailed Han crossbred lambs

We investigated the metabolizable protein (MP) supply in lambs at different levels of feed intake. Twelve Dorper x thin-tailed Han crossbred ram lambs (41.3 +/- 2.8 kg body weight) fitted with ruminal and duodenal cannulae were randomly assigned to one of three levels (n=4 lambs each) of dry matter intake: ad libitum (AL) intake and 70% or 50% of AL intake. Digesta flow was measured using a dual-marker system (Yb and Co). A lower duodenal flow of rumen undegraded nitrogen (RUN) was measured for the 50% AL group (P < 0.05) compared with the other two groups. For lambs of the AL group, the ratio of microbial N/duodenal non-ammonia nitrogen (NAN) was lower (P < 0.05), and the ratio of RUN/duodenal NAN was higher (P < 0.05) compared with the other two groups. The ratio of RUN/N intake was higher for the 70% AL and 50% AL groups compared with that for the AL group (P < 0.05). Apparent post-ruminal N digestibility increased with decreasing feed intake (P < 0.05).A linear correlation was established to predict MP supply (g/day) from the intake of organic matter (kg/day) or crude protein (g/day): MP = 0.036 (+/- 0.004) x organic matter intake + 50.47 (+/- 4.43), R-2 =0.89; MP= 0.27 (+/- 0.033) x crude protein intake +49.88 (+/- 4.93), R-2 = 0.87. The current results provide preliminary data of MP requirements for growth of Dorper crossbred lambs. (C) 2015 Elsevier B.V. All rights reserved.