Abstract
We investigated the metabolizable protein (MP) supply in lambs at different levels of feed intake. Twelve Dorper×thin-tailed Han crossbred ram lambs (41.3±2.8kg 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)×organic matter intake+50.47 (±4.43), R2=0.89; MP=0.27 (±0.033)×crude protein intake+49.88 (±4.93), R2=0.87. The current results provide preliminary data of MP requirements for growth of Dorper crossbred lambs.
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