Effects of pasture grazing or storage feeding and concentrate input between 5·5 and 11 months of age on the performance and carcass composition of bulls and on subsequent growth and carcass composition at 620 kg live weight

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Abstract
A 3-year experiment has been carried out to compare systems of bull beef production involving pasture grazing and continuous storage feeding and to examine the effects of sward surface height and concentrate input from 5·5 to 11 months of age on grazing behaviour, growth rate and body composition at the end of the treatment period and on subsequent growth rate and carcass composition at commercial slaughter weight. Animals were either set-stocked at pasture to maintain sward surface heights of 6·5 and 10·0 cm or were given grass silage (725 g digestible organic matter per kg dry matter (DM)) supplemented with 0·8, 1·6, 2·4, 3·2 and 4·0 kg cereal-based concentrates (188 g crude protein per kg DM) per head daily. Half of the animals grazed at each sward height were given 1 -6 kg concentrates per head daily while the remainder received no supplement. A total of 255 continental beef breed × Friesian calves which were initially 198 kg live weight were used. From 11 months of age until slaughter at a mean live weight of 620 kg all animals were given grass silage supplemented with 3 kg cereal-based concentrate DM per head daily.Reducing sward surface height from 10·0 to 6·5 cm increased the proportion of time spent grazing (P < 0·001), reduced the proportion of time involved in other activities and reduced live-weight gain (P < 0·001) from 1·21 to 0·84 kg/day. Offering concentrates at pasture reduced (P < 0·001) the proportion of time spent grazing (the effect being greater with the animals grazing the shorter swards) but did not affect the performance of the animals grazing the taller swards and produced only a modest increase in the live-weight gain (70 g/kg concentrates) of those grazing the shorter swards. At the end of the treatment period, the carcasses of the animals which had been given silage contained proportionally 0·39 more lipid than those of animals which had been at pasture and had the same growth rate. Differences in live weight at 11 months of age due to differences in feeding from 5·5 to 11 months were largely retained until the end of a 7-month period of realimentation while differences in carcass composition at II months were eliminated by slaughter at a constant live weight of 622 kg.

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