Structural optimization of selection index of breeding qualities of bulls-producers of the Simmental breed

In the Russian Federation, there are virtually no studies on the optimization of the breeding index structure for genetic improvement of dairy cattle breeds. The article presents the results of optimization of the breeding index equation for assessing the breeding value of bulls-producers of the Simmental cattle breed according to the characteristics of their daughters’ milk productivity. We describe the approach of complex assessment of breeding value of animals based on inclusion of five production traits of dairy productivity: milk yield (kg), mass fraction of fat and protein in milk (%), amount of milk fat and protein (kg). We calculated values of the complex breeding value of bulls-producers using genetic evaluations performed by the BLUP method on a sample of animals from five Russia’s regions (Belgorod, Kursk, Voronezh, Orel oblasts, and Altai Krai). For genetic improvement of a particular breeding trait or combination of traits in formation of breeding groups of animals with their subsequent selection in pairs, we propose to carry out additional ranking of producers by construction of optimized breeding indices with modified structures of equations including different indices of milk productivity and their combinations. By calculating the rank correlation coefficient, we determined the level of interrelations between the same bulls evaluated by the general breeding index and the optimized breeding indices (limits of variation were from -0.504 to +0.924). We alco carried out generalization of the obtained data with the results of the previously published studies on the optimization of the equations of the index of complex breeding value in the paleo-pasture cattle population, red-pasture and black-pasture breeds.