| Summary: | Data from a commercial pig population undergoing selection were analysed in order to estimate genetic variation and covariation. The data were collected between 1982 and 1988 and consisted of performance test records (food conversion ratio (FCR), total weight gain, average daily gain (ADG) and average daily food intake (ADFI) on test and four ultrasonic backfat measurements at shoulder, loin, C and K positions) for boars and gilts plus reproduction records (total number born, number born alive (NBA), litter weight, average piglet weight (PWt) and gestation length) on sows. Landrace and Large White breeds were subject to the same environment. The test regime varied between sexes; gilts were housed in groups, boars in pairs and gilts were fed on a lower feed scale than their boar contemporaries. During the data collection period the test regime changed for boars and gilts, leaving distinct groups of animals tested under different regimes (Test Management Groups or TMGs). All analyses presented were performed using Individual Animal Model methods, which take account of all known relationships and selection on the trait, or traits, in the analysis. Univariate heritability estimates for performance test traits were slightly lower on average than literature estimates. Differences in variance component and parameter estimates were observed between TMGs which could be explained by changes in feed regime, health status and halothane status; effects of selection were confounded with these. Univariate heritability and repeatability estimates for reproduction traits were consistent with the available literature estimates. Univariate analyses produced no evidence of maternal genetic variation for performance test or reproduction traits, while significant but generally low estimates of common litter of birth effects were detected for some performance test traits.
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