MATERNAL HETEROSIS IN SWINE: REPRODUCTIVE PERFORMANCE AND DAM PRODUCTIVITY

The objectives of this study were to estimate the heterosis of crossbred gilts for ovulation rate and the maternal heterosis of crossbred gilts for dam productivity. A total of 470 gilts were saved for breeding of which 72 were considered reproductive failures. Estimates of heterosis were made from 193 pregnant gilts slaughtered 30 days postbreeding (106 crossbred and 87 purebred)and 192 litters farrowed (98 three-breed and 94 two-breed cross). The reproductive failure rate for all gilts was 15.3% with there being very little difference~ between purebred and crossbred gilts. Estimates of heterosis for ovulation rate were not significantly different from zero, although crossbred gilts of all breed groups consistently had fewer corpora lutea per gilt than purebreds (13.48 vs 13.03). The embryo survival rate for embryos from crossbred gilts was 9.52 ± 3.23% higher than for embryos from purebred gilts. No other estimate of maternal heterosis for traits measured on gilts slaughtered 30 days postbreeding was significantlY different from zero, although crossbred gilts consistently had more embryos per litter 30 days postbreeding (10.77 vs 9.95). Three-breed cross embryos were also .46 ± .36 mm longer than two-breed cross embryos. Crossbred gilts consistently had larger and heavier litters at all ages and raised a larger percentage of their pigs from birth to weaning than did purebred gilts. Litters from crossbred gilts contained .68 ± .46, .96 ± .39 and .98 ± .36 more pigs and weighed .69 ± .54, 5.69 ± 1.86 and 10.46 ± 3.87 kg more than litters from purebred gilts at birth, 21 and 42 days, respectively. The survival rate from birth to weaning was 4.50 + 2.61% higher for pigs from crossbred gilts than for pigs from purebred gilts