Effects of Inbreeding, Selection, Linecrossing and Topcrossing in Swine. III. Predicting Combining Ability and General Conclusions

Abstract

Data on 6 lines of inbred swine and on the two-, three- and four-line crosses between them and on results of using these in topcrosses are compared for predictability from one mating system to another. The following appeared to have predictive value: pig weaning weight in inbreds with two-line crosses classified by dam-line; pig 5-month weight in two- and three-line crosses and topcrosses classified by sire-line with each other; and the ratio of 5-month to 56-day pig weights in inbreds with 5-month weight in two- and three-line crosses and topcrosses classified by sire-line. Subdivision of variance in two-line crosses for 56-day pig weights indicated that maternal effects are more important than general combining ability and that the opposite is true for 5-month pig weights. Neither showed evidence of specific combining ability. It was also indicated that there was a negative genetic correlation between additive effects in the pig and the maternal effects of the line. The possible applications of the results to the genetic improvement of swine are discussed.