Direct and maternal genetic effects on first litter size, maturation age, and animal size in Finnish minks.

Variance components were estimated for maturing age, first litter size, and animal size in Finnish minks. The fitted animal models had direct genetic and maternal genetic effects, litter effects, and maternal environmental effects. Multivariate analysis was performed to determine covariances between the traits. Maternal effects represented a significant source of phenotypic variance in the maturation age and animal size. For litter size, maternal effects were not as clear. Moreover, in maturation age and animal size, the covariance between the direct additive effect and the maternal additive effect was negative. In addition, litter effect variances were larger than maternal variances for all traits. Therefore, it is crucial to also estimate environmental effects common to littermates for these traits. Direct heritability and the response to selection are overestimated, especially for maturation age and also for animal size, when maternal and common litter effects are not considered.