GENETIC AND PHENOTYPIC RELATIONSHIPS BETWEEN PERFORMANCE-TEST AND REPRODUCTION TRAITS IN LARGE WHITE-PIGS

Genetic and phenotypic relationships between performance test and repr oduction traits were estimated, after five generations of divergent se lection for components of efficient lean growth, in a population of La rge White pigs. On ad-libitum feeding, a total of 4334 pigs were perfo rmance rested, of which 884 selected gifts had measurements of reprodu ction traits. On a restricted feeding regime, 1558 pigs were tested, w hich included 336 selected gilts with reproduction records. For pigs g iven food ad libitum, genetic correlations between litter weights at b irth and weaning with daily food intake (0.48 and 0.42, s.e. 0.16) and with growth rate on test (0.65 and 0.52) were positive, but correlati ons with backfat depths were nor significantly different from zero. Fo r pigs given food at a restricted level, litter birth weight was posit ively genetically correlated with growth rate (0.50, s.e. 0.18) and ne gatively correlated with backfat depths (-0.48, s.e. 0.16). Phenotypic and environmental correlations between performance test and reproduct ion traits were all less than 0.10 in magnitude, for pigs tested on ei ther feeding regime. The variation in backfat depth enabled detection of a non-linear relationship between predicted breeding values for lit ter weight at birth with predicted breeding values for average backfat depth of farrowing gilts performance tested on ad-libitum feeding, bu t not for gilts tested on restricted feeding. The positive genetic cor relations between growth rate and daily food intake with litter traits suggested that selection strategies which change growth and daily foo d intake may result in relatively greater genetic changes in piglet gr owth rate than in litter size.