The Inheritance of Prolificacy in Swine1

Publisher Website
Google Scholar
Abstract
Estimates of heritability of litter size in swine were determined by three methods for both total pigs farrowed and pigs farrowed alive. All of the estimates fell within the range 8.8 percent to 17.6 percent. The mean estimates were 13.6 percent from live pigs farrowed and 14.5 percent from total pigs. Estimates of repeatability were 12.8 percent for live pigs and 13.3 percent for total pigs farrowed. There is close agreement between these estimates of heritability and repeatability and it may be concluded that variations in size of litter due to inheritance must be due very largely to the average effects of genes. Heritability of litter size determined from these data is close to 14 percent. Since the average coefficient of inbreeding of the females used in this study was 0.19, the genetic variance may be expected to be 19 percent less than that of an outbred population. Thus on the basis of an outbred population the heritability of the number of pigs farrowed is estimated at approximately 17 percent. According to results obtained in this and other studies relating to heritability of litter size progress in increasing fertility by selection in an outbred stock low in fertility would be very slow if simultaneous selection for other characteristics continued. The most rapid progress would come from a greatly increased selection differential, such as would result from an outcross with individuals selected on the basis of fertility from a breed or line known to be high in fertility. The most rapid progress in increasing fertility within a breed should be expected to result from the development of fertile inbred lines and their use in outcrossing throughout the breed.