The response of store lambs to dietary supplements of fish meal 1. Effects of forage-to-concentrate ratio

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Abstract
Forty-eight individually-penned lambs (mean live weight 31-4 kg) were offered one of four diets, to investigate response to a supplement of fish meal (0 and 100 g dry matter (DM) per kg M) given with diets of either 60: 40 or 40: 60 forage-to-concentrate ratio. Nitrogen (N) degradability in the rumen and fractional outflow rates of protein supplements were determined. The diets were formulated such that the lambs received about 3 or 9 g undegradable rumen N per kg DM. The diets were given daily to provide sufficient metabolizable energy for maintenance and 150 g gain, and were adjusted according to live weight at weekly intervals.Fish-meal supplementation improved daily growth over a 49-day period (P < 0·001) and enhanced N retention (P < 0·001). Live-weight gain was also marginally improved on the high-forage diets. (P < 0-05), but there was no protein supplement × forage-to-concentrate ratio interaction. Apparent digestibility of acid detergent fibre was improved by the fish-meal supplement on the high-concentrate diet.The four diets were also given to rumen-fistulated sheep. The high-concentrate diet was associated with a higher molar proportion of propionate (P < 0·05) and a lower proportion of acetate (P < 0·001). Rumen concentrations of ammonia tended to be maintained at higher levels throughout the day by the fish-meal supplement.