The response of store lambs to dietary supplements of fish meal 2. effects of level of feeding

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Abstract
Forty-eight, individually-penned lambs (mean live weight 31·4 kg) were given diets with or without fish meal (0 and 90 g intake daily) in sufficient quantities to provide energy for maintenance and either 100, 150 or 200 g daily gain. Nitrogen (N) degradability in the rumen and fractional outflow rates of protein supplements were determined and the diets formulated such that the lambs received about 2·2 and 6·7 g undegradable rumen N daily on all three feeding levels.Live-weight gains were generally greater during the first 3 weeks than during the final 4 weeks of the experiment. Lambs given fish meal had greater gains (P < 0·001) throughout the experiment, but there was a feeding level x protein interaction (P < 0·05) during the first 3 weeks, such that the difference between diets with or without fish meal was greater at the highest feeding level.Retention of N increased with feeding level (P < 0·001) and was greatest when fish meal was given (P < 0·001). There was a feeding level x protein interaction (P < 0·05) for g N retained per 100 g N digested; N retention increased with feeding level only when fish meal was given.