Preweaning Survival in Swine: Heritability of Direct and Maternal Effects

Abstract

Summary The heritabilities of direct and maternal effects on litter survival to weaning (LS) were estimated from records of 1,243 litters of pigs from the Nebraska Gene Pool population born from 1968 to 1981. Heritabilities were estimated by: (1) weighted least-squares regressions of average survival for litters of sons on average survival for litters of their sire, (2) nested analysis of variance with LS fitted to a model including year-line and sire of litter, (3) weighted least-squares regression of average survival for the litter of daughters on the survival of the litter of their dam and (4) nested analysis of variance with LS fitted to a model including year-line and sire of dam of litter. Analyses were conducted with and without adjustment for litter size born. Estimates of the heritability of direct effects from methods 1 and 2 were negative. Adjustment to a common litter size born had no effect. If direct effects are considered to be negligible, as indicated by these analyses, then LS may be considered a trait of the dam. The heritability of maternal effects estimated from daughter-dam regression was .01 +- .02. The estimate of heritability of maternal effects obtained from analysis 4 was .07 + .03. Again, there were no effects from adjustment to a common litter size born. These estimates were not significantly different and the pooled estimate was .03 + .02. These analyses indicate that some additive genetic variance might exist for maternal effects but none for direct effects on LS. Selection for increased survival is not expected to be successful.