EFFECTS OF DATE OF WEANING ON POSTWEANING PERFORMANCE OF BULL CALVES OF THREE BREED GROUPS

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Abstract
The effects of weaning date on feedlot performance and carcass characteristics of 367 bull calves weaned 1 mo apart were compared in a 2-yr study at the University of Alberta ranch at Kinsella, Alberta. The calves belonged to three distinct breed groups. Calves were weaned either on 1 Oct. or 1 Nov., at which time they averaged 157 ± 1.5 and 189 ± 1.7 d of age, respectively. After a 4-wk postweaning adjustment period, calves in each group were fed a mixed diet containing 90% concentrate and 10% hay. During the period between the two weaning dates early-weaned calves gained more (P < 0.05) than their unweaned contemporaries, while the performance of the two groups during their respective adjustment periods was similar. The late-weaned group gained 175 g d−1 more (P < 0.05) and consumed 800 g d−1 more feed (P < 0.05) during the 140-d feedlot test while feed efficiency did not differ between the two groups. Average daily rate of gain from birth to 1 Oct. had a significant influence on feedlot gain (b = 0.42). Although late-weaned calves had a higher rate of growth during the feedlot test, their early-weaned contemporaries were 14.3 kg heavier and 7 d younger at slaughter. Significant differences in gain and carcass traits were observed between the three breed groups, but the interaction between breed group and weaning date was not significant, indicating that calves of different genetic backgrounds respond similarly to the effects of age at weaning. The results indicate that under Alberta's climatic conditions and despite lower feedlot gains, weaning calves 1 mo early is a viable alternative to the customary weaning date. Key words: Beef calves, bulls, weaning date, carcass traits