The effect of additive treatment of grass silage and the food additive avoparcin on the response of calves to supplementation of silage-based diets with fish meal

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Abstract
Two experiments have been carried out to examine the effects of the fermentation quality of grass silage and the inclusion of avoparcin in the diet on the response in the performance of calves to supplementation of silage-based diets with fish meal. The eight treatments used in each experiment consisted of untreated and formic acid-treated (2·5 1/t) silages offered ad libitum and supplemented with either barley (B) or a barley/fish meal (BF) concentrate (200 g fish meal per kg), without or with 150 mg avoparcin per head daily in a 2 × 2 × 2 factorial design. All animals received 1·25 and 1·0 kg concentrates per head daily in experiments 1 and 2 respectively. In each experiment, the diets were offered to 40 castrated male cattle which were initially 126 and 110 kg live weight in experiments 1 and 2 respectively. On average over the two experiments the untreated and formic acid-treated silages contained 24·8 and 24·5 g nitrogen (N) per kg dry matter (DM); 475 and 571 g protein N per kg total N; 76 and 62 g ammonia-N per kg total N and 45-9 and 27·5 g volatile fatty acids per kg DM respectively. Silage DM intakes for the untreated silages supplemented with B and BF and the acid-treated silages supplemented with B and BF without avoparcin and for the untreated silages supplemented with B and BF and the acid-treated silages supplemented with B and BF with avoparcin were 3·0, 3·2, 3·2, 3·0, 2·9, 3·0, 3·0 and 3·2 (s.e. 0·16) kg/day respectively. Live-weight gains for the corresponding treatments were 0·97, 1·12, 0·98, 1·01, 1·00, 1·07, 1·10 and 1·13 (s.e. 0·032) kg/day respectively. It is concluded that the inclusion of fish meal in diets based on well preserved, grass silage and barley did not affect intake and produced a small response (70 g/day) in the live-weight gain of calves. The inclusion of avoparcin in the diet did not significantly affect the response to fish meal.