Date of this Version
Selection for an index of ovulation rate (OR) and embryo (fetal) survival rate (ES) to 50 d of gestation (I = 10.6 x OR + 72.6 x ES) was practiced for five generations in a line that was a composite population of the Large White and Landrace breeds of swine. A control line sampled from the same population was selected randomly and mated. Ovulation rate and number of fetuses (FETS) were measured by laparotomy and ES was calculated as FETS/OR. The select line averaged 43 litters by 18 sires and the control line averaged 42 litters by 15 sires per generation. Each generation, all females available in the select line (average of 147) were mated and laparotomized, but only selected females were farrowed. One-half of the females underwent laparotomy in the control line. Inbreeding coefficients at generation five averaged 5.34% for the select line and 4.59% for the control line. Regressions of the difference between means of the lines on generation number were .57 ± .11 for OR, -.013 ± .0096 for ES, .20 ± .20 for FETS and 5.10 ± 1.76 for I. Realized heritability for I was .30 ± .09. Heritabilities estimated by regression of daughter on dam were .17 ± .07 for OR, .18 ± .09 for ES and .08 ± .10 for FETS, and the genetic correlation between OR and ES was estimated to be -.56 ± .24. The increase in number of pigs per litter at birth was .19 ± .14 per generation.