Days to calving in Angus cattle: Genetic and environmental effects, and covariances with other traits

Abstract

Abstract Field data from Angus herds in Australia were used to examine systematic effects influencing days to calving (DC) and to estimate genetic correlations between DC and other traits. Days to calving was computed as the interval in days between the first joining date each year for a cow under paddock mating and subsequent calving. Non-calvers received a predicted DC record. Herd, year-month of joining, service sire, previous joining season and age at joining significantly influenced DC. Lactation status of older cows did not affect DC. Calving difficulty in first calf heifers had no observed effect on their subsequent DC record. Alternative methods for allocating a predicted or ‘penalty’ DC record for non-calvers were investigated. Estimates of covariances among DC records from different parities, and between DC and calving success and weight traits were obtained by Restricted Maximum Likelihood, using a derivative-free algorithm. Very high genetic correlations among repeat DC records ( r g = 0.85) and between DC and calving success ( r g = −0.97) were observed. Genetic correlations between early weight traits and DC were positive and low, but not significantly different from zero.