IMPLICATIONS OF USING AN AVERAGE RELATIONSHIP MATRIX IN GENETIC EVALUATION OF 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 1000 times with either ran dom mating or sequential selection continuing for eight breeding cycle s. In the selection case, candidates were ranked on estimated breeding values (EBVs) calculated from the MME with an animal model and the av erage A. Variances of the EBVs and prediction errors were computed. Th e results showed that the average A incorrectly perceives both the var iance of family sizes among males and the variance loss due to selecti on to be smaller. This leads to an overestimation of genetic trend.