EFFECTS OF WINTER SUPPLEMENTARY CONCENTRATE LEVEL ON THE PERFORMANCE OF STEERS SLAUGHTERED IMMEDIATELY OR FOLLOWING A PERIOD AT PASTURE

The objective of the present study was to quantify the production resp onses to supplementary concentrates during the second winter in silage -fed cattle slaughtered at the end of winter or following a period at pasture. Sixty-four spring-born Charolais x Friesian steers (500 kg li veweight at the start of this experiment) were reared together from ca lifhood to the end of their second grazing season. Four animals, chose n at random, were then slaughtered to provide initial carcass data. Th e remaining 60 animals were assigned, on weight, to six treatment grou ps in a 3 (0, 3 or 6 kg concentrates per head daily with silage ad lib itum in winter) x 2 (spring or autumn slaughtered) factorial experimen t. Half of the animals from each concentrate level were slaughtered at the end of winter (spring slaughtered) and the remainder were slaught ered towards the end of the following grazing season (autumn slaughter ed). The duration of the winter and subsequent grazing periods was 172 days each. Mean silage dry matter intakes and liveweight gains during winter for the 0, 3 and 6 kg/day concentrate levels were 8.3, 6.3 and 5.0 (s.e. 0.23) kg/day and 311, 664 and 893 (s.e. 24.0) g/day, respec tively. Corresponding liveweight gains during the following grazing se ason were 908, 675 and 470 (s.e. 17.0) g/day. Carcass weights for the 0, 3 and 6 kg/day concentrate levels were 298, 336 and 363, and 385 40 6 and 410 (s.e. 5.3) kg for the spring and autumn slaughtered animals, respectively. Linear regressions of daily liveweight gain in winter ( y1), liveweight gain at pasture (y2), on concentrate level in winter ( x) were y1 = 328 + 96 (s.e. 11.3) x and y2 = 903 - 73 (s.e. 8.6) x. It is concluded that, due to compensatory growth at pasture, the optimum level of supplementary concentrates is higher for animals slaughtered at the end of winter than for animals destined to spend the following summer at pasture.