Correlated responses to selection for reproductive traits in swine

Correlated responses to selection for increased litter size or decreased age at puberty in swine (eight generations) after previous selection for ovulation rate (nine generations) were evaluated. Selection for litter size resulted in an increase of.83 $\pm$.35 fully formed pigs per litter in first parity gilts, and the response was maintained in second and third parity sows. Litter size response was due to an increase of 1.30 $\pm$.54 eggs in ovulation rate and.66 $\pm$ 1.28 pigs in uterine capacity, but no significant changes were observed in uterine dimensions. About 25% of the increase in litter size could be explained by a reduction in the number of mummified pigs at birth, an indication that uterine capacity in late gestation was increased. Selection for litter size resulted in no change in litter weight at birth, but in a reduction in both number of pigs weaned and individual weaning weight. Pigs selected for litter size had delayed growth to 90 kg and delayed puberty in females, but little change in backfat thickness. Selection for decreased age at puberty resulted in minor changes in litter size, but in a reduction in litter weight at birth and weaning, even though number of pigs weaned was not affected. Pigs selected for younger age at puberty had increased backfat thickness but little change in growth rate to 90 kg. Genetic parameters for embryonic survival to 50 days of gestation estimated in a line of pigs selected for an index of ovulation rate and embryo survival were.01 to.04 for the heritability of direct effects,.01 to.04 for the heritability of maternal effects and $-$.21 to $-$.72 for the correlation between direct and maternal effects