Abstract:
Proc. Aust. Soc. Anim. Prod. Vol. 17 STRAIGHT- AND CROSS-BRED HEIFER MILK PRODUCTION IN THE DEVON AND HEREFORD BREEDS D.J. 425 JOHNSTON* and P.M. HORN* Calves from cross-bred beef cows are generally heavier at weaning than calves from straight-breds; this difference is largely attributed to the greater milk production of the cross-breds (Cundiff et al. 1974). The present experiment examined milk production in cross-bred and straight-bred heifers and the growth of their calves at three stages of lactation. The straight- and reciprocal cross-bred heifer progeny of a two-breed cross (D> and Hereford (H) breeds were mated at 15 months to Red between the Devon Angus bulls. A sub-sample of 40 of these heifers across the four genotypes was used to estimate milk yield by the technique using oxytocin injection and teat (Butson et al. 19801, at 5, 12 and 22 weeks of lactation. * cannulation Individual heifer body weights and fat scores (1 = thin, 5 = fat) were averaged for the three milkings. Milk yields for individual animals from the three milkings were adjusted to an average cow-calf separation time of 440 minutes and analysed as repeated measures in a multiple regression model. TABLE 1: Differences in heifer genotypes and the effects of heifer fat score and weight, calf sex and age on milk yield (kg). Cross-bred heifers had a higher milk yield (P<O.Ol) than the straight-breds at all stages of lactation8 the average heterosis being 39%. There was no difference in milk yield between either the straight-breds, or the reciprocal crosses (P>O.OS). These differences in milk yield accounted for most of the differences in growth rate between calf genotype. Heifer milk yield declined with increasing body fat score. BUTSON, S., BERG, R.T. and HARDIN, R.T. (1980). Can. J. An' . SC'. m:727. CUNDIFF, L.V., GREGORY, K.E., SCHWULST, F.J. and KOCH, R.Mlm(197&.% Anim. Sci &728. * Animal Genetics and Breeding Unit, University of New England, Armidale NSW 2350.
