ANIMAL-MODEL ESTIMATION OF GENETIC-PARAMETERS AND RESPONSE TO SELECTION FOR LITTER SIZE AND WEIGHT, GROWTH, AND BACKFAT IN CLOSED SEEDSTOCK POPULATIONS OF LARGE WHITE AND LANDRACE SWINE

Records from 2,495 litters and 14,605 Landrace and Large White pigs from two farms, but established from the same base population and run as replicated selection lines, were analyzed. Selection within herd was on estimated breeding values weighted by economic values. Animal models and REML procedures were used to estimate genetic, phenotypic, and environmental parameters for the number of pigs born alive (NBA), litter weight at 21 d (LW), average daily gain from approximately 30 to 104 kg (ADG), and backfat thickness adjusted to 104 kg (BF). Random animal genetic effects (o), permanent (NBA and LW) or litter (ADG and BF) environmental effects, maternal genetic effects (m), and the covariance between o and m were sequentially added to the model. Estimates of total heritability calculated from all data (h(t)2 = sigma(o)2 + 1/2sigma(m)2 + 3/2sigma(om)) ranged from .01 to . 14 for NBA, from .18 to .22 for LW, from .23 to .34 for ADG, and from .40 to .50 for BF. Maternal genetic variance was from 2.4 to 3.8% of phenotypic variance in NBA, from 1.2 to 3.6% in LW, from .5 to 1.5% in ADG, and from 1.9 to 3.4% in BF. The correlation between o and m was -.07 for NBA, -.25 for LW, -.34 for ADG, and -.26 for BF. Permanent environmental effects explained from 16 to 17% of total phenotypic variation for NBA and from 1.6 to 5.3% for LW. Approximately 7% of the variation in ADG and 5% in BF was due to litter environmental effects. Genetic trends were .012 pigs/yr for NBA, .25 kg/yr for LW, 5.91 g/yr for ADG, and -.063 mm/yr for BF.