Estimates of heritability and repeatability for reproductive traits in Australian beef cattle

Abstract

Data originated from four Hereford stud herds, the Angus herd maintained at the New South Wales Department of Agriculture's Research Centre, Trangie, and tropical cattle ( Bos indicus × Box taurus crossbreds) at the C.S.I.R.O. National Cattle Breeding Station, Belmont, near Rockhampton. Estimates of variance components and resulting heritabilities and repeatabilities were obtained by Restricted Maximum Likelihood, using a derivative-free algorithm, for a total of seven traits assuming an Animal Model. For males, scrotal circumference was moderately to highly heritable with pooled estimates of 53, 42 and 26% for Herefords, Angus and tropical crossbreds, respectively, while the pooled heritability estimate for serving capacity was 22% in Herefords and zero in Angus. Estimates for fertilizing ability, defined as the proportion of a bull's mates which conceived or calved, were essentially zero. On the female side, variables describing cows' lifetime reproductive performance, were distinguished from traits pertaining to individual breeding seasons. Pooled heritability estimates for calving rate, defined as number of calves divided by number of opportunities to calve, were 7% for Herefords, 11% for Angus and 17% for tropical crossbreds. Corresponding values for number of calves were 7,9 and 36%, respectively. Days to calving was calculated as the interval between start of the joining period and calving. Cows which did not calve were assigned a predicted value derived from normal theory. Pooled heritabilities were 5% for Herefords, 8% for Angus and 9% for tropical crossbreds with pertaining repeatabilities of 22,10 and 18%. Correspondingly, for calving success, coded as 0 or 1, heritability estimates were 8, 2 and 8%, and repeatabilities were 91, 2 and 10%, respectively.