Stochastic simulation of the influence of insemination on the estimation of breeding value and its reliability

Insemination is used less commonly in the population of beef cattle than in dairy cattle. As a consequence, herds are genetically isolated and their comparison is difficult. The objective of the paper was to evaluate the impact of the use of reference sires in insemination on the estimation of breeding value and its reliability by means of stochastic simulation based on a single addition of calves to the basic set. Simulation was divided into three variants according to the connectedness calves through sires (variant 1 - unrelated calves, variant 2 calves related between HYS but unrelated within HYS, variant 3 - calves related within and between HYS). The degree of connectedness was determined by computation of genetic drift variance (GDV). The average value of GDV in the basic set was 0.71. In our study the highest values of GDV were reached in simulated variant 3, in which the relationship increased not only between HYS but also within HYS. The lowest values of GDV were in variant 2, when the relationship increased only between HYS (simulated calves after reference sires did not have any halfsibs in HYS). The single use of reference sires in one generation to make herds connected slightly increased the average coefficient of reliability from 0.121 to 0.145 (by 2.4%) in the whole set. But this increase from 0.24 to 0.33 (by 8.9%) was observed only in animals that were directly connected through reference sires. The increase in reliability was mainly due to an increase in the number of contemporaries. A decrease in the effective number of sires' offspring was an indirect consequence of the increase in the connectedness of the set and higher use of reference sires in insemination. This is the reason why the increase in the connectedness of the set influenced the reliability of breeding value of the whole set less than we would expect. The use of reference sires influenced the fluctuation of breeding values. The use of a higher number of reference sires in insemination with only one offspring in each of the connected herds appeared as the most suitable approach from the aspect of the connectedness of the set and reliability of breeding value estimation. A marked influence of herd connectedness on the estimation of breeding value and its reliability, and on the result of breeding, is to be expected after reference sires have been used in several successive generations.