Effect of level of barley supplementation on the performance of continental × Holstein Friesian bulls given grass silage

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Abstract
Forty Charolais and 40 Limousin × Holstein Friesian bulls, 8 months old and weighing 315 kg live weight at the start of the experiment, were given grass silage to appetite throughout. From 315 to 425 kg live weight they received: no supplement (S0), 1 kg (S1), 2 kg (S2) or 4 kg (S4) of a rolled barley supplement per head per day. After a mean treatment live weight of 425 kg had been achieved for each breed, the daily supplement of all treatments was changed to 3 kg of rolled barley per head per day until individual animals were adjudged to have attained a European Community (EC) external fatness score of 3 to 4L, at which point they were slaughtered. Daily growth rates from 315 to 425 kg live weight were 0·67, 0·82, 0·94 and 1·25 (s.e.d. 0·042) kg for treatments S0, S1, S2 and S4 respectively. Following the change of supplement rate at 425 kg live weight, daily gains were 1·46, 1·36, 1·27 and 1·16 (s.e.d. 0·051) kg/day, giving overall gains of 0·99, 1·05, 1·08 and 1·19 (s.e.d. 0·033) kg/day respectively. The numbers of days taken to achieve slaughter condition from the start of the trial at 315 kg were 277, 251, 243 and 207 (s.e.d. 5·3) days respectively. Bulls were slaughtered at 17·0, 16·2, 15·9 and 14·7 months of age and produced carcass weights of 330, 324, 322 and 305 (s.e.d. 6·5) kg respectively. Silage dry-matter intakes were 5·9, 5·1, 4·8 and 4·2 kg/day during the initial phase when differential supplement levels were being given and 7·0, 6·8, 6·2 and 5·8 respectively during the finishing period when all groups were being given 3 kg barley supplement daily. Food conversion ratios (kg dry matter intake per kg gain) were 9·1, 7·3, 6·9 and 5·8 during the initial phase and 6·4, 6·9, 6·9 and 7·2 respectively after 425 kg live weight. It is concluded that barley supplements of 0 to 2 kg/day offered with high-quality grass silage during the growing stage (8 to 12 months of age), followed by at least 3 kg/day will produce finished bulls at an average of 325 kg carcass weight at 16 to 17 months of age. A higher level of 4 kg barley during the growing stage will reduce the slaughter period to approximately 15 months of age but carcass weight will also be reduced. Further studies are required to define the precise level of barley supplement during this earlier period.