The Genetics of Brahman Cow Weight in Northern Australia and its Relationship with Female Reproductive Performance

Annual weights from 1025 Brahman cows, commencing at their first annual mating (average 2 years of age) were evaluated in a univariate random regression analysis. Results showed that cow weight from 2 to 7 years was heritable (h² = 0.31 to 0.53). The analysis was extended to include a second dependent variable describing female reproductive performance (age at puberty (AP), lactation anoestrus interval (LAI) or lifetime annual weaning rate (LAWR)). Genetic correlations of AP with cow weight were low (rg = -0.09 to 0.03), while lower LAI and higher LAWR displayed moderate genetic relationships with higher early cow weight which decreased with cow age (rg=-0.28 to 0.02 and 0.37 to 0.11 respectively). Results show that if Brahman breeders in northern Australia select to improve female reproductive performance, correlated responses in cow weight would be small and expected to diminish with cow age.