Feedlotting of slow-growing lambs at different stages of growth

Abstract

The lightest 80 lambs at six weeks of age in a flock of 341 were divided into 4 groups, A-D. Groups A, B, and C were weaned at 6, 12 and 18 weeks of age respectively; group D was managed under normal pasture grazing conditions until weaning at 24 weeks of age. Immediately upon weaning, groups A, B, and C were placed in a feedlot and offered a diet of 86 per cent whole barley grain and 14 per cent of a pelleted mixture of fishmeal, straw, molasses, minerals and vitamins; decreasing daily amounts of lucerne chaff were offered for the first 15 days to reduce the incidence of digestive upsets. After six weeks in the feedlot each group was returned to the flock. While in the feedlot, four lambs in group A and one lamb in group B died. Two lambs in group A and four lambs in group D died while grazing. All feedlot groups lost weight initially, groups A and B for 14 days and group C for 7 days. Feedlotting of groups A and B did not improve their growth rates compared with group D. Only 15 and 20 per cent respectively of lambs grew faster than group D lambs. Group C lambs were significantly heavier (P < 0.05) at the end of their feedlot period than group D lambs and 74 per cent of them grew faster than the mean growth rate of group D lambs. Excluding the initial weight losses in the feedlots, 50 per cent, 50 per cent and 84 per cent of lambs in groups A, B and C grew at rates faster than the mean corresponding rates for group D. It is concluded that some slow-growing lambs are capable of responding to preferential feeding treatment but the variability in responses within a group does not favour the adoption of a feedlot procedure as used in this experiment.