A note on the response of store lambs to iso-nitrogenous diets containing rapeseed meal or fish meal

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Abstract
Live-weight gain responses were investigated using 36 individually penned lambs (mean live weight 35·2 kg) given three sodium hydroxide treated straw-based diets: low-protein, low-rapeseed meal (control) diet; high protein, high-rapeseed meal (HR) diet; or high-protein, fish meal (FM) diet. The diets were formulated to provide 3 or 9 g undegradable nitrogen per kg dry matter (DM) respectively for the diets without or with fish meal. Diets were offered once a day in a 50: 50 forage-to-concentrate ratio in amounts calculated to support maintenance plus 150 g gain and were adjusted weekly according to live weight. Live-weight gain, measured for 7 weeks, was improved by the FM diet only (P < 0·05).The three diets were given also to rumen-fistulated sheep. The FM diet maintained higher rumen ammonia concentrations during most of the day. The FM and HR diets reduced rumen solid particle outflow rate (P < 0·05) and increased the effective degradability of DM and acid-detergent fibre.