Reciprocal crossbreeding of Angus and Hereford cattle 1. Growth of heifers and steers from birth to the yearling stage

Maternal (dam breed), direct (sire breed), and heterosis effects on growth were estimated from purebred Angus (A x A), purebred Hereford (H x H), and crossbred (H x A and A x H) steers and heifers bred at the Waikite Land Development block near Rotorua over a 4‐year period. There were higher losses of calves from Hereford than Angus dams calving at 2 years‐of‐age, but no differences for older dams. Survival rate, both pre‐ and post‐weaning, was higher for crossbred than purebred calves. Data from 934 calves alive at 5‐month weaning and 897 calves alive at 13 months‐of‐age were analysed for liveweights and liveweight gains from birth to 13 months. Relative to Angus calves, Herefords were born 7 days later and were 3 kg heavier at birth, because of both maternal and direct effects. Both breeds had similar maternal effects on weaning and on subsequent weights. Post‐weaning weights and weight gains for the direct effect favoured the Hereford. Comparison of purebred calves with the reciprocal crosses showed significant ( P < 0.01) heterosis for all liveweights and liveweight gains, increasing from 3.0070 at birth to 5.1 % at weaning and 8.6% at 13 months‐of‐age. In general, heterosis was higher in steer than heifer calves, particularly for weights at or close to weaning. Over the 4‐year experimental period, 49 Angus and 34 Hereford sires were used. Sire variance components were estimated simultaneously with the breed and heterosis effects and used to derive paternal half‐sib genetic parameters. Heritability estimates increased from weaning (0.17) to 10 months‐of‐age (0.36) and tended to be higher in heifer than steer calves. Heritabilities of pre‐ and post‐weaning gains were low (0.12 and 0.07) with the exception of postweaning gain for steer calves (0.31).