Postpartum anestrous interval in first-lactation beef and dairy-beef crossbred cows

In New Zealand, beef-breeding cows are required to wean a calf every year, and the weight of calf at weaning is a major driver of the efficiency of the breeding cow. Weaning weight can be increased by increasing milk yield of the cow such as by incorporating dairy breed genetics into the breeding cows, and by having early born calves which are, therefore, older at weaning. This experiment examined postpartum anestrous interval and pregnancy rate to rebreeding in 109 beef-breed and beef-cross-dairy breed first-lactation cows suckling their own calves. Cows with a Jersey component had a shorter postpartum anestrous interval than cows without (90 versus 97101 days; P<0.05). Pregnancy rates after 42 days of joining with bulls were 8397% for straight-bred Angus, Angus-cross-Friesian, Angus-cross-Jersey and Angus-cross-Kiwicross (Friesian-cross-Jersey) cows, but only 41% for straight-bred Friesian cows (P<0.05). For every day younger heifers reached puberty, postpartum anestrous interval was reduced by 0.07 0.02 days (P<0.01) indicating that age at puberty could be used as a predictor of subsequent fertility. The Jersey-component cows offered advantages in fertility traits and may be worthwhile incorporating into beef-breeding cow herds. © 2012 CSIRO.