|Van Vleck, Lloyd|
Submitted to: Genetics and Molecular Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2007
Publication Date: 9/30/2007
Citation: Chen, C., Johnson, R.K., Newman, S., Van Vleck, L.D. 2007. A general review of competition genetic effects with an emphasis on swine breeding. Genetics and Molecular Research. 6(3):594-606. Interpretive Summary: Selection in pigs does not always result in the expected genetic change. The methods and estimated heritabilities and genetic correlations used to predict selection response do not consider possible competitive effects among pigs in the same pen. Previous estimates of heritabilities and genetic correlations and the framework for considering competition effects in predicting selection response were reviewed. Failure to consider competitive effects such as agonistic behaviors which may have a genetic component may partially explain why response to selection has been less than predicted. An approach to considering both animal and competition effects based on multilevel selection has theoretical advantages.
Technical Abstract: A review of previous studies will be presented on estimates of genetic parameters and less than expected responses to selection with traditional breeding approaches, on correlations between competitive behavior and growth performance, on theoretical frameworks for selection incorporating competition effects among individuals and on practical methods for incorporating competition effects in breeding programs. The resemblance between relatives is often measured as the covariance due to additive genetic variance. Genetic factors, however, are not the only sources contributing to the covariance between relatives. Environmental components such as competition effects might increase or reduce resemblance between relatives. Animal-welfare concerns become an issue when some animals tend to be aggressive and cause injury under poor environmental conditions. Production efficiency could be expected to improve without compromising animal well-being by changes in the genetic selection process to include competition effects. In the past, selection theory has been developed within the framework of non-interacting genotypes in a population. Some behavioral traits are speculated to have genetic components (e.g., agonistic behavior) which indicate competition among individuals might have an impact on genetic evaluations. Selection based only on direct additive models without consideration of the effect of competition might over estimate expected response to selection. Such effects might partially explain why response to selection has varied or has been less than predicted. This review will discuss previous studies and an approach to joint selection for direct and competition genetic effects based on multilevel selection.