Genetic parameters for growth rate and backfat in Canadian Yorkshire, Landrace, Duroc, and Hampshire pigs.

Records on 47,360 Yorkshire, 28,762 Landrace, 14,020 Duroc, and 9,983 Hampshire pigs for backfat depth and days to 100 kg made between 1989 and 1992 in herds on the Ontario Swine Improvement Program (OSIP) were used to estimate additive genetic (animal), common environmental (litter), and residual variances and covariances of the two traits. Analysis was by the DFREML program of K. Meyer using a multiple-trait individual animal model with fixed effects of genetic groups and herd-year-season-sex and random effects of animal, litter, and residual. A complete relationship matrix was used. Heritabilities were .51, .53, .55, and .50 for backfat and .31, .30, .26, and .32 for days to 100 kg in Yorkshire, Landrace, Duroc, and Hampshire, respectively. Genetic correlations between backfat and days to 100 kg were -.16, -.06, -.17, and -.10 for Yorkshire, Landrace, Duroc, and Hampshire. Respective phenotypic correlations were -.08, -.04, -.12, and -.09. Litter effects were large, particularly for days to 100 kg. Resulting common environmental (c2) effects were .11, .10, .10, and .11 for backfat and .26, .27, .29, and .22 for days to 100 kg for Yorkshire, Landrace, Duroc, and Hampshire. Estimates were highly consistent across breeds and average heritabilities of backfat and days to 100 kg were .52 and .30. Corresponding average c2 effects were .10 and .26. Average genetic and phenotypic correlations between backfat and days to 100 kg were -.13 and -.08.