Maintaining Fitness by Within Breed Selection

Abstract

Genetic improvement of productivity in livestock has been very successful in the past. Improvement of traits related to fitness, such as health, fertility and disease resistance, however, has proven more difficult. Reasons are (i) low heritabilities, (ii) difficulty to record traits related to fitness, (iii) genotype by environment interaction, e.g. between commercial and breeding environment, (iv) presence of heritable effects other than the direct genetic effect of the individual itself. This paper argues that improvement of fitness related traits is not fundamentally different from improvement of other traits. Important factors are (i) the identification of all heritable components affecting trait values, (ii) the collection of phenotypic data from commercial environments combined with marker assisted estimation of breeding values (so-called “genomic selection”). Marker assisted breeding value estimation does not threaten genetic diversity, and is operationally much easier to use than methods based on QTL mapping. The paper concludes with a section on heritable social interactions among individuals. Results show that heritable social interactions represent an extra level of variation which may increase the heritable variation available to breeders to values considerably higher than the usual additive genetic variance. First results in pigs and poultry are promising, but more data analysis is needed to substantiate the relevance of heritable social interactions in other species.