Relative milk yields and calf growth rates in two beef cattle types.

Abstract

Animal production in Australia RELATIVE MILK YIELDS AND CALF GROWTH RATES IN TWO BEEF CATTLE TYPES R. SPRIVULIS*, R.K. MITCHELL*, F.F. DIXON*, M.J. CARRICK** and C.S. EDWARDS** The selection experiment at Wokalup Research Station compares straight-bred Herefords and 'Wokalups', the latter formed by interbreeding a four-way cross of Charolais, Brahman, Friesian and Angus or Hereford. Replacements in each herd are selected on pre-weaning growth rate. Because of the expected effect on the preweaning growth of calves of maternal milk supply and length of lactation, an aim of the selection experiment is to document the phenotypic and genetic relationships among these variables. A study was begun in 1979 to investigate the effects of breed, age of dam and stage of lactation on the growth of calves, using two methods to estimate milk yield. This paper reports on the relationship between calf growth rate and dam's milk yield estimated by weighing the calf, suckling and re-weighing twice on the day of estimation. Twelve cows of each breed were matched for age, time of calving and sex of calf. All cows calved in April-May and were run as a single herd on annual pasture at a rate of 1.1 cows per ha. Bull calves were castrated on 5 November and weaned on 29 November. The 24 hour milk yields, corrected to 4% butterfat, are shown below (Z/d). Milk yields were affected by breed and age of cow (PL 0.01) and by period of lactation (P/(,0.05), There were no significant interactions involving breed, age or period effects on milk yields. Calf growth rates were affected by breed and period of lactation (P< 0.01) but the effect of dam age was not significant. However there was an interaction between breed and dam age effects on calf growth. A high positive correlation between calf growth and cow milk yield was observed in the Herefords but it was low in the Wokalups. This suggests that where milk supply exceeds a certain level (relative to calf appetite) that it has little effect on the growth rate of young calves. The importance of milk intake declines again later when the calf begins to eat relatively more pasture. * Department of Agriculture, Bunbury, W.A. 6230 ** Department of Agriculture, Jarrah Road, South Perth, W.A. 6151. 506