Over the past five decades the art of animal breeding has rapidly advanced into an exacting science with such developments as BLUP estimation of breeding values and REML estimates of variance components. These new methods promise much faster advances in genetic improvement than previously possible.  However, actual responses have often fallen short of expectation and in some cases responses were worse than with previous methods.  The reason for these disappointing results can only be due to assumptions inherent to the BLUP models used.  The most commonly used and recognized assumption is that of an additive model, i.e. no dominance or higher order epistasis. However, a more important, and less recognized, assumption is that of non-interacting genotypes, i.e. genotypes do not compete.  If higher producing animals tend to be more competitive; the effect of selection is to increase competition.  Competition has the effect of lowering productivity of other animals that are in direct contention.  As such, ignoring competitive interactions invalidates the BLUP model used and negates many advantages of this technology and could in fact make it a liability.  Muir (1996) and Muir and Craig (1998) examined the use of group selection to address this problem and to select for adaptation of layers to multiple-hen cages.  Annual percentage mortality of the selected line in multiple-bird cages decreased from 68% to 8.8% in 5 generations while eggs per hen housed increased from 91 to 237. The dramatic improvement in livability demonstrates that adaptability and well-being of these birds were improved by group selection.  However group selection requires that families be housed together and selected as a group.  As a result, the rate of inbreeding may increases rapidly, which would limit long term response.  In this report we present a method for incorporating competitive effects in the mixed model equations, thereby allowing individual selection, and demonstrate effectiveness of this approach with a selection experiment using Japanese quail. 

William M Muir, A. P Schinckel

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 2002. Session 14, , 14.07, 2002
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