Breed and environmental factors affecting birth weight in Victorian beef cattle

Abstract

Birth weights of 2929 Angus, Hereford and Poll Hereford calves born between 1963 and 1970 on six properties in Victoria, Australia, were analysed to provide correction factors for the effect of dam age, calf sex and calving time. The unadjusted mean birth weight of all calves was 30.9 ± 4.5 kg. Year of calving affected birth weight significantly on four out of five properties, although the effects of year and property were partially confounded. Calves from two, three and four-year-old dams were 15, 8 and 6 per cent lighter respectively, than calves from mature (5 to 8 years) dams. Male calves were significantly heavier by 1.86 kg than female calves; twin calves were significantly lighter by 7.0 kg than single-born calves. Calving time affected birth weight significantly on five out of six properties, with an increase in birth weight of approximately 1.0 kg per month from mid-autumn to mid-winter.