GENETIC-PARAMETERS FOR LITTER SIZE OF DIFFERENT PARITIES IN DUROC, LANDRACE, AND LARGE WHITE SOWS

Univariate and multivariate analyses were performed for litter size bo rn alive and at 21 d in Duroc, Landrace, and Large White sows raised i n southern Brazil. Variance and covariance components were estimated f or first, second, and third parities, and for different sets of pariti es using DFREML under animal models with direct and maternal genetic e ffects. Additive direct genetic variances were different for breeds an d for parities within breeds. Most estimates of heritability of direct effects were higher than the average value of .10 reported in the lit erature, and were two to five times the size of their standard errors, indicating that opportunities for genetic improvement of litter size in these breeds may be greater than assumed on the basis of previous r eports. Maternal additive genetic variances were higher in second than in first or third parities, but were significant only for Large White sows. Genetic correlations for all breeds were high between first and third, and between second and third parities, but were low, in the ra nge of .32 and .48, between first and second parities. For-this reason , multiple-trait genetic evaluation of animals for litter size should be used to estimate breeding values when first and later parity record s are involved.