The Contribution of Social Effects to Heritable Variation in Finishing Traits of Domestic Pigs (Sus scrofa)

Abstract

Social interactions among individuals are ubiquitous both in animals and in plants, and in natural as well as domestic populations. These interactions affect both the direction and the magnitude of responses to selection and are a key factor in evolutionary success of species and in the design of breeding schemes in agriculture. At present, however, very little is known of the contribution of social effects to heritable variance in trait values. Here we present estimates of the direct and social genetic variance in growth rate, feed intake, back fat thickness, and muscle depth in a population of 14,032 domestic pigs with known pedigree. Results show that social effects contribute the vast majority of heritable variance in growth rate and feed intake in this population. Total heritable variance expressed relative to phenotypic variance was 71% for growth rate and 70% for feed intake. These values clearly exceed the usual range of heritability for those traits. Back fat thickness and muscle depth showed no heritable variance due to social effects. Our results suggest that genetic improvement in agriculture can be substantially advanced by redirecting breeding schemes, so as to capture heritable variance due to social effects. S OCIAL interactions among individuals are ubiquitous both in animals and in plants, and in natural as well as domestic populations. These interactions affect both the direction and the magnitude of responses to artificial and natural selection (e.g., Wilham 1963;Hamilton 1964;Griffing 1967;Wade 1977;Frank 1998;Wolf et al. 1998). Social interactions, therefore, are a key factor in the design of artificial breeding programs in domestic species (Denison et al. 2003;Muir 2005) and for the outcome of evolutionary processes in natural populations (e.g., Hamilton 1964;Queller 1992;Frank 1998;Keller 1999;Clutton-Brock 2002).In agriculture, reduction of competitive behaviors is critical for improving animal well-being and productivity in confined high-intensity rearing conditions (Craig and Muir 1996;Kestemont et al. 2003;Muir 2005). Both theoretical and empirical work has shown that the relatedness among interacting individuals and the distribution of selection pressure over the individual and group levels are key factors for response to selection

The quantitative genetics of indirect genetic effects: a selective review of modelling issues

“…A farm may, for example, consist of units of 8-12 groups each, which introduces the risk of confounding environmental unit or unit  batch effects with IGEs, even when random group effects are included in the statistical model. Compared with a previous study (Bergsma et al, 2008), Bergsma et al (2013), for example, found substantially smaller IGEs in growth rate in domestic pigs due to an increase in the data set and a change in the statistical model.…”

“…In populations consisting of small groups this covariance may be negative, which requires fitting a correlation between the residual terms of group mates (Bijma et al, 2007b). With large groups, the non-genetic covariance between group mates is likely positive, and can be accounted for by including a random groupeffect in the model (Arango et al, 2005;Bergsma et al, 2008). In populations of plants, including trees, spatial residual variance structures may be fitted to account for local environmental trend and for the non-genetic component of the indirect effect.…”

Resilience in farm animals: biology, management, breeding and implications for animal welfare

“…Thus, genetic selection for resilience may benefit from selection on performance of the group rather than the individual (Muir 2005), especially where social stressors are likely to be a major cause of environmental stress to farm animals (Muir 1996;Bergsma et al 2008;Bolhuis et al 2009). Genetic models to disentangle direct and social effects have been developed by Bijma et al (2007).…”

Across-Line SNP Association Study for Direct and Associative Effects on Feather Damage in Laying Hens

“…Bijma et al (2007b) showed that non-genetic covariance among group mates can bias the estimates of genetic associative effects. Although we modelled social interactions differently, we fitted a random group effect to asses the magnitude of such non-genetic covariance in our analysis (see Bergsma et al 2008). The significance of the estimates of the SNPs effects from models [3] and [4] decreased only fractionally and did not affect the presented results at all.…”