Genetic aspects of intervals from weaning to estrus in swine.

Genetic variation in interval from weaning to estrus, and genetic relationships with traits commonly under selection were studied using data from an eight-generation selection experiment on a short interval from weaning to estrus, and data from an American breeding company. From the biological background and the distribution of data it appears that interval from weaning to estrus is either normal or prolonged. Selection for a short interval reduced the average interval by reducing the incidence of prolonged intervals only. Sows on units of the breeding company studied with a prolonged interval had consistently more favorable estimated breeding values for backfat and growth rate, than sows with a normal interval. Analysis of data from the selection experiment did not confirm this. Model studies showed that extending the number of traits under selection with a 0/1 trait, representing normal and prolonged intervals, gives the highest response ineach of the traits under selection