The effect of age at weaning on the health status of bull calves in a feedlot.

Incidence of morbidity and mortality in a feedlot were compared among 381 bull calves weaned one month apart (October 3 and November 1). The calves were 156 and 192 days old at weaning in the earlier and later weaned groups, respectively. Following an adjustment period, the calves were fed a mixed finishing diet containing 90% concentrate ad lib for 140 days in a feedlot. The rate of morbidity did not differ significantly between the two weaning groups. Sick calves in the earlier weaned group had a longer treatment period than those in the later weaned group (3.2 vs 1.4 days, p<0.05). Infections of the respiratory tract were the major cause of sickness and most of the respiratory infections occurred in the early stages of the feedlot period. The frequency of respiratory infections was higher among the earlier weaned calves compared with that in the later weaned group (p<0.01) indicating a higher susceptibility to these infections when calves were weaned at younger ages. Bloat was the second most common health problem among the bulls; however, its incidence did not differ between the two groups (p>0.05). The rate of mortality did not differ significantly between the two groups.