Effects of Inbreeding and Outbreeding in Purebred Hampshire and Duroc Swine

Reproductive and growth records from purebred Hampshire and Duroc swine were analyzed for effects of inbreeding and dominance gene action by single-trait analysis with Method R. Estimates were obtained for number born alive (NBA), 21-d litter weight (LWT), days to 104.5kg (DAYS), and backfat at 104.5kg. (BF). Final estimates were obtained from six samples for each trait. Regression coefficients for 10% inbreeding were –0.09 and –0.06 for NBA, –0.15 and 0.002 (kg) for LWT, 3.2 and 2.6 for DAYS, and 0.0 and 0.0 for BF in Hampshire and Duroc analysis, respectively. Estimates of additive and dominance variance, expressed as a percentage of phenotypic variation, were 8.8 and 1.6 for NBA, 9.7 and 6.1 for LWT, 25.4 and 9.3 for DAYS, and 50.2 and 2.6 for BF in the Hampshire population. Estimates of additive and dominance variance were 8.3 and 5.7 for NBA, 9.0 and 8.4 for LWT, 33.4 and 13.8 for DAYS, and 53.6 and 5.5 for BF in the Duroc population, respectively. Inbreeding was found to negatively influence phenotypic performance for reproduction and growth. Mate selection programs including dominance genetic effects may be able to enhance performance and allow for increased profitability.