INDIVIDUAL ANIMAL-MODEL ESTIMATES OF GENETIC-PARAMETERS FOR PERFORMANCE-TEST TRAITS OF MALE AND FEMALE LANDRACE PIGS TESTED IN A COMMERCIALNUCLEUS HERD

Estimates of heritabilities, common litter of birth effects and additi ve maternal genetic effects were produced for ultrasonic backfat depth , average daily food intake, average daily gain and food conversion ra tio of Landrace boars and gifts. Boars and gifts were performance test ed under different regimes. A bivariate derivative-free restricted max imum likelihood procedure was used to estimate genetic correlations be tween the performance test traits as recorded in the two sexes. Herita bility estimates from the analysis including the common litter of birt h effect tended to be towards the low end of the range of recently pub lished estimates. This may reflect either population specific effects, such as effects of long-term selection, or the use of an individual a nimal model. Estimates of the common litter of birth effect were aroun d 0.05, and generally had a significant effect upon the fit of the mod el, while additive maternal genetic effect estimates were negligible. Therefore, it is expected that omission of maternal effects from model s for evaluation by best linear unbiased prediction will not hinder ge netic progress. Inclusion of common litter of birth effects would be r ecommended, although this result may not hold for populations given fo od ad libitum. The estimates of genetic correlations between performan ce test traits of boars and gilts indicate that the levels of genotype -environment interaction (G x E) and genotype-sex interaction were low across most traits and data sets, with all genetic correlation estima tes lying between 0.8 and 1.0. The lowest estimates of rite genetic co rrelations, which were observed in data sets where the environments ap peared to differ most, indicate that G x E interactions may be a probl em in populations where males and females ave subject to test regimes with greater differences than those seen here.