IMPLICATIONS OF USING AN AVERAGE RELATIONSHIP MATRIX IN GENETIC EVALUATION FOR A POPULATION USING MULTIPLE-SIRE MATINGS

Ambiguous paternity can be incorporated into the mixed model equations (MME) by including the average numerator relationship matrix (average A), which averages the true sire-offspring relationship over the puta tive sires. A previous study has shown that some overestimation of gen etic trend results from this substitution. A population of 40 breeding females and 2 breeding males was simulated 1,000 times with either ra ndom mating or sequential selection continuing for 8 breeding cycles. In the selection case candidates were ranked on estimated breeding val ues (EBVs) calculated from the MME with an animal model and the averag e A. Variances of the EBVs and prediction errors were computed. The re sults showed the average A incorrectly perceives both the variance of family sizes among males and the variance loss due to selection to be smaller. This will lead to an overestimation of genetic trend.