SCOPE FOR GENETIC EVALUATION AND SELECTION OF BEEF-CATTLE FOR GROWTH TO WEANING WHEN BIRTH DATES ARE NOT RECORDED

Estimates of (co)variance components and genetic parameters were obtai ned for a preweaning weight, recorded between 2 and 5 months after bir th, and the subsequent gain till weaning for two herds in a selection experiment in Western Australia. Analyses were carried out both accoun ting for age at weighing and assuming birth dates and thus ages were u nknown. On adjusting for the interval between weighings, preweaning ga in appeared to be independent of age and equally heritable to weaning weight. Estimates of the direct genetic correlation between preweaning gain and weaning weight (adjusted for age) were 0.9 or higher, while both genetic and permanent environmental maternal correlations were cl ose to unity. Implications for the use of preweaning weight as an alte rnative selection criterion to weaning weight when birth dates axe not recorded are discussed.