ESTIMATION OF CROSSBREEDING PARAMETERS BETWEEN LARGE WHITE AND MEISHAN PORCINE BREEDS .3. DOMINANCE AND EPISTATIC COMPONENTS OF HETEROSIS ON REPRODUCTIVE TRAITS

A crossbreeding experiment using Large White (LW) and Meishan (MS) pig strains was conducted. Dominance, additive x additive and dominance x dominance epistatic components of direct and maternal heterosis effec ts were investigated for various litter productivity and sow traits: t otal number born (TNB), number born alive (NBA), number weaned (NW), l itter weight at birth (LWB) and at 21 d (LW21), either adjusted or not for litter size, sow weight loss (SWL), sow total (SFC) and maximum ( SFCM) feed consumption, sow feed efficiency - computed as SFC per pigl et weaned (SFC/NW) or per unit of litter weight gain (SFC/LWG) - durin g lactation. Data from 1 148 litters farrowed by 250 sows were analyse d. Models involving all possible combinations of dominance and epistat ic parameters were compared for goodness of fit on the basis of their mean squared error (MSE). The model with the lowest MSE was then used to estimate crossbreeding parameters. Models involving dominance effec ts only for maternal heterosis had the lowest MSE for all litter produ ctivity traits. Dominance also appeared as the main component of direc t heterosis effects on litter productivity traits. Favourable dominanc e and unfavourable epistatic effects contributed to direct heterosis e ffects for all sow traits except SFCM. Epistatic effects were additive x additive effects for SFC/NW and dominance x dominance effects for S WL, SFC and SFC/LWG. Estimates of direct, maternal and grand-maternal breed effects are presented. A possible contribution of cytoplasmic ef fects to between-breed variation is also hypothesized.