Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 22, 2002
Publication Date: September 1, 2002
Citation: Cassady, J.P., Young, L.D., Leymaster, K.A. 2002. Heterosis and recombination effects on pig growth and carcass traits. Journal of Animal Science. 80:2286-2302. Interpretive Summary: Estimates of genetic effects are useful to evaluate pig breeds and to develop efficient crossbreeding systems. Growth and carcass traits were influenced by breed of pig and dam, but seldom by breed of maternal grandam. Crossbred pigs grew more rapidly than purebred pigs, but differences between purebred and crossbred pigs were less important for carcass traits. Growth of young pigs raised by purebred or crossbred dams often differed, probably due to the number of littermates and competition for milk. Relative to progeny of purebred parents, new allelic combinations among genes exist in progeny of crossbred sires and dams. These new combinations tended to increase growth, daily feed intake, and carcass length, while decreasing backfat. Loin muscle area was reduced by new combinations in one group of breeds, but not in another group. In general, crossbred sires and dams can be used in mating systems without concern for adverse effects of new genetic combinations. New combinations tended to produce neutral or favorable effects.
Technical Abstract: The primary objective was to estimate heterosis and recombination effects on growth and carcass traits of two different four-breed composite populations of pigs. Experiment 1 (Exp1) included purebred and crossbred pigs originating from Yorkshire, Landrace, Large White, and Chester White breeds, and Experiment 2 (Exp2) included pigs from Duroc, Hampshire, Pietrain, and Spot breeds. Data were recorded on purebred pigs, two-breed cross pigs, and pigs from generations F1 through F6, where F1 pigs were the first generation of a four-breed cross. Mixed-model analyses were done separately by experiment, fitting an animal model. Fixed effects included farrowing group and sex for growth traits and farrowing group for carcass traits. Included as covariates in all models were direct, maternal, and maternal grandam breed effects, direct and maternal heterosis effects, and a direct recombination effect. Recombination is the breakup of additive epistatic effects present in purebreds during gamete formation by crossbred parents. Effects of direct heterosis significantly increased weights at birth, 14, 56, 70, and 154 d of age in Exp1. Effects of direct heterosis significantly increased ADG from birth to 14, 28 to 56, and 70 to 154 d of age in Exp1. In Exp2, effect of direct heterosis significantly increased weights and ADG at all ages. In Exp1, recombination significantly reduced loin muscle area. In Exp2, recombination significantly increased weights at birth, 14, 28, and 56 d, ADFI from 70 to 154 d, and ADFI adjusted for ADG. The correlation between maternal heterosis and recombination effects for all traits in Exp1 and Exp2 was approximately -0.90. Maternal heterosis and recombination effects were estimable, but greatly confounded.