Index-in-retrospect and breeding objectives characterizing genetic improvement programmes for South African Nguni cattle
The goals of this research were to document the historical selection applied by Nguni breeders that contributed to the national genetic evaluation scheme, and to offer prospective breeding objectives to guide future selection practices. Genetic selection differentials, weighted by number of offspring, and unweighted, were calculated for the recorded traits, and were used to quantify differences between natural and imposed selection. Index-in-retrospect methods were used to quantify differences between the traits in selection that were applied. Economic values for the prospective breeding objectives were derived through simulation. Results indicate that relatively little directional selection has been applied to Nguni as a breed, and that historically bulls and heifers were selected according to divergent criteria. Breeding objectives indicated that production, profitability and sustainability goals were largely complementary, but reflected a change from past selection practices. Breeders are advised to be intentional and consistent in the application of selection criteria.
Keywords: Breeding goals; production systems; selection; sexual dimorphism simulation