Breed effects and heterosis for productivity traits at first calving of Angus, Holstein Friesian, Jersey and crossbred beef cows

摘要

Feed requirements for maintenance contribute a large proportion of the feed requirements of a beef cow so lighter cows may be more efficient producers of weaned calves, provided that such cows do not result in a comparative reduction in calf weaning weight. Beef-cross-dairy cows have increased milk yield compared with straight-bred beef cows and have the potential to wean heavier calves. Crossbred cows may also offer potential increases in production through heterosis. This experiment examined the performance of straight-bred Angus (AA), Holstein Friesian (FF) and Jersey (JJ) cows and of Angus-sired F1 crossbreds with Holstein Friesian (AF), Jersey (AJ) and Holstein Friesian-cross-Jersey (Kiwicross; AK) cows to identify breed and heterosis effects on milk intake and liveweight of calves and liveweight, reproductive performance and fatness of cows in their first lactation. Days to calving and weaning rate from first joining were similar among genotypes, but only 50% of FF cows conceived to second joining, compared with 90-98% for the other genotypes (P < 0.05). Estimated milk intake of calves was least (P < 0.05) for calves born to AA cows, and was generally similar (P > 0.05) among calves born to crossbred cows. There were positive heterosis effects between Angus and Jersey and between Angus and Holstein Friesian on milk intake of the calf. Straight-bred FF cows weaned the heaviest calves (least-squaresmean + s.e.: 241 +/- 5 kg; P < 0.05). Calves born to AF and AK cows were weaned at similar liveweight (229 +/- 3 kg and 226 +/- 4 kg, respectively; P > 0.05), and were heavier (P < 0.05) than calves born to JJ and AJ cows, which were similar (208 +/- 5 kg and 215 +/- 3 kg, respectively; P > 0.05). Calves born to AA cows were lightest at weaning (196 +/- 3 kg; P < 0.05). Estimates of heterosis for weaning weight were 11 +/- 4 kg (P < 0.01) between Angus and Holstein Friesian, and 14 +/- 4 kg (P < 0.001) between Angus and Jersey. Angus-cross-dairy cows offered production advantages over straight-bred AA cows as dam lines in a terminal cross. These advantages were partially due to heterosis