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 Uni versity of Alberta Ranch at Kinsella, Alberta, Canada. Three synthetic line s, two of which were predominantly beef breeds (BS1 and BS2) and one with a pproximately 60% dairy breeding (DS), were used and 995 records were analyz ed. Cows from each line were randomly allotted to the early or late breedin g 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 assista nce, 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, earl y 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 we aning 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-w eaning 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 calv ing and weaning (P < 0.01), suggesting that DS cattle benefited more by lat e calving. The late-calving management system appears to be a viable option for cow-calf production in Alberta.