Correlated responses of pre- and postweaning growth and backfat thickness to six generations of selection for ovulation rate or prenatal survival in French Large White pigs

¹ INRA UR337 Station de Génétique Quantitative et Appliquée F-78350 Jouy-en-Josas
² INRA UE332 Domaine de Galle, F-18520 Avord

^* To whom correspondence should be addressed. E-mail: jean-pierre.bidanel{at}jouy.inra.fr.

	Abstract

Correlated effects of selection for components of litter size on growth and backfat thickness were estimated using data from 3 pig lines derived from the same base population of Large White. Two lines were selected for 6 generations on either high ovulation rate at puberty (OR) or high prenatal survival corrected for ovulation rate in the first two parities (PS). The third line was an unselected control (C). Genetic parameters for individual piglet weight at birth (IWB), at 3 wk of age (IW3W), and at weaning (IWW), average daily gain from birth to weaning (ADGBW), from weaning to 10 wk of age (ADGPW), and from 25 kg to 90 kg BW (ADGT), and age (AGET) and average backfat thickness (ABT) at 90 kg BW were estimated using REML methodology applied to a multivariate animal model. In addition to fixed effects, the model included the common environment of birth litter, as well as direct and maternal additive genetic effects as random effects. Genetic trends were estimated by computing differences between OR or PS and C lines at each generation using both least squares (LS) and mixed model (MM) methodology. Average genetic trends for direct and maternal effects were computed by regressing line differences on generation number. Estimates of direct and maternal heritabilities were, respectively, 0.10, 0.12, 0.20, 0.24, and 0.41, and 0.17, 0.33, 0.32, 0.41, and 0.21 (SE = 0.03 to 0.04) for IWB, IW3W, IWW, ADGBW, and ADGPW. Genetic correlations between direct and maternal effects were moderately negative for IWB (-0.21 ± 0.18), but larger for the 4 other traits (-0.59 to -0.74). Maternal effects were non significant and were removed from final analyses of ADGT, AGET and ABT. Direct heritability estimates were 0.34, 0.46 and 0.21 (SE = 0.03 to 0.05) for ADGT, AGET, and ABT, respectively. Direct and maternal genetic correlations of OR with performance traits were non significant, with the exception of maternal correlations with IWB (-0.28 ± 0.13) and ADGPW (0.23 ± 0.11) and direct correlation with AGET (-0.23 ± 0.09). PS also had low direct, but moderate to strong maternal genetic correlations (-0.34 to -0.65) with performance traits. The only significant genetic trends were a negative maternal trend for IBW in OR line and favorable direct trends for postweaning growth (ADGT and AGET) in both lines. Selection for components of litter size has limited effects on growth and backfat thickness, though it slightly reduces birth weight and improves postweaning growth.

Key Words: genetic parameters, growth, ovulation rate, pigs, prenatal survival, selection experiment