Effects of early versus late spring calving on beef cow calf productivity

Early (April) vs. late (May/June) calving was compared over 3 yr at the University of Alberta Ranch at Kinsella, Alberta, Canada. Three synthetic lines, two of which were predominantly beef breeds (BS1 and BS2) and one with approximately 60% dairy breeding (DS), were used and 995 records were analyzed. Cows from each line were randomly allotted to the early or late breeding schedules at the time of breeding. The same bulls bred cows in their own line, beginning in June and in August for two 6-wk periods. Calving season had no significant effect (P > 0.05) on pregnancy rate (%), calving assistance, calving and weaning rate (%), adjusted off-test weight or post-weaning ADG, suggesting that late calving can be a viable management option. Birth weights of all calves were significantly lower in the early group than in the late group (38.9 vs. 41.2 kg, P < 0.01). In the BSI and BS2 lines, early calves had higher adjusted pre-weaning ADG: BSI (1.18 vs. 1.11 kg d(-1) P < 0.01), BS2 (1.12 vs. 1.05 kg d(-1), P < 0.01) but the differences in the DS line were not significant (P > 0.05). The early calves were older at weaning and therefore were expected to have higher pre-weaning ADG. The fact that the late-born calves in the DS line equalled the early calves in pre-weaning ADG indicates that they were growing relatively faster. Late calving DS heifers had significantly higher weights (P < 0.01) at breeding in June, higher ADG to breeding, and cows had higher body condition scores at calving and weaning (P < 0.01), suggesting that DS cattle benefited more by late calving. The late-calving management system appears to be a viable option for cow-calf production in Alberta.