Genetics of heifer age at puberty in Australian Angus cattle

Age at puberty has become a key trait in the genetic evaluation of female reproduction for tropically adapted beef breeds in northern Australia. This study aimed to characterise the trait in Australian Bos taurus seedstock heifers and determine the degree to which it, and associated traits, were under genetic control. Angus heifers (N = 3093) from nine seedstock herds were serially ultrasound scanned to determine age at puberty, via detection of their first corpus luteum, at approximately 4 week intervals from 10.5 to 13.6 months of age, when heifers were synchronised for artificial insemination. Results showed that only 53% of Angus heifers were pubertal at synchronisation for AI and that within this category, age at puberty had a heritability of 0.33. When a penalised record (maximum age at puberty for a contemporary group plus 21 days) was included for heifers that were not pubertal into mating, heritability increased to 0.42. For sires with EBV accuracy greater than 0.7, EBVs for age at puberty ranged from -69 to +70 days. The ability of heifers to conceive early in their first mating season has been linked to lifetime reproductive performance. These results suggest that the proportion of heifers that have reached puberty as they enter their first mating is significantly less than 100% and that opportunities exist to monitor and apply selection to improve age at puberty in Australian Angus heifers.