The effect of herd of origin by year on post-weaning traits of young beef bulls at centralized testing centres in South Africa

The effects of herd of origin by year on the average daily gain (ADG), average daily feed intake (DFI), shoulder height (SDH) and scrotal circumference (SCR) of beef bulls at centralized test centres in South Africa were investigated using data of Bonsmara cattle. Data consisted of post-weaning traits of beef bulls tested between 1990 and 2003, with available weaning weight (WWT) and weaning management group information as well as weaning weights of their contemporaries. A multiple-trait animal model including ADG, DFI, SDH and SCR, together with WWT was used. The model for WWT (adjusted to 205 days of age and age of dam by sex of calf classes) included the fixed effect of management group and random effects of direct additive genetic and dam effects, while the model for post-weaning traits included fixed effects of test group and age of the bull at the end of test (fitted as linear and quadratic regressions) and random effects of direct additive genetic and herd of origin by year (HY) effects. Variance components were estimated using REML procedures. Heritability estimates were 0.27, 0.34, 0.36, 0.51 and 0.46 for WWT, ADG, DFI, SDH and SCR, respectively. The contribution of HY effects to the phenotypic variance of ADG, DFI, SDH and SCR were 9%, 10%, 6% and 5%, respectively. Inclusion of HY effect resulted in the re-ranking of sires, with rank correlations ranging from 0.86 to 0.98 among the top sires, across traits. These results suggest that the HY effect should be included in the model for the national genetic evaluation of post-weaning traits of beef bulls measured at centralized testing centres in South Africa. _______________________________________________________________________________________