ESTIMATION OF DIRECT AND MATERNAL GENETIC (CO) VARIANCES FOR SURVIVALWITHIN LITTERS OF PIGLETS

Variation in piglets weaned per sow per year is the main factor explai ning differences in income between piglet producers. This parameter is the result of prolificacy of sows and survival rare of piglets. Data on 54500 piglets born between 1988 and 1994 at four nucleus breeding u nits of a pig breeding organization were used in an analysis of piglet survival. Animals were from two different dam lines. Piglet survival until weaning was considered and management was aimed at weaning at 28 days of age. Variance and covariance components were obtained using m ixed models which included direct genetic and maternal genetic effects . In addition, the model included sex, breed, parity and herd-year-sea son as fixed effect, birth weight as covariable and sow as permanent e nvironmental effect. Bayesian analysis, implemented using Gibbs sampli ng, was used to estimate the effects and parameters. Heritability of d irect and maternal genetic effects was 0.11 (+/-0.01) and 0.09 (+/-0.0 1), respectively, in the full model. Genetic correlation between direc t and maternal genetic effects was -0.56 (+/-0.06). Consequences of ex cluding maternal genetic effects or permanent environmental effects we re studied. Based on the presented results it is concluded that simult aneous selection on maternal and direct genetic merit offers the oppor tunity to increase piglet survival.