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Effects of Inbreeding, Selection, Linecrossing and Topcrossing in Swine. III. Predicting Combining Ability and General Conclusions¹

University of Wisconsin, Madison

Abstract

Data on six lines of inbred swine and on the two-, three- and four-line crosses between them and on the results of using these in topcrosses are compared for their 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 the 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 the additive effects in the pig and the maternal effects of the line.

Possible applications of the results to the genetic improvement of swine are discussed.

¹ Paper 683 from the Department of Genetics and the Department of Animal Husbandry, University of Wisconsin, in cooperation with the Regional Swine Breeding Laboratory, AHRD, ARS, USDA. Published with the approval of the Director of the Agricultural Experiment Station.

² Present address: Department of Animal Husbandry, University of California, Davis, California.

³ The authors wish to acknowledge aid from the following: The Quebec Agricultural Research Council, for a scholarship to the senior author, and Dr. M. Kimura, who suggested the method of analyzing the two-line cross data.