Genetic homogenisation of birth weight in rabbits: Indirect selection response for uterine horn characteristics

Abstract

A divergent selection experiment on within-litter homogeneity of birth weight in rabbits was carried out at the INRA experimental farm at Auzeville. The two lines were created by selecting breeding does and bucks from the female strain AGP22 bred at the Grimaud Frères Sélection Company. This involved a new model incorporating a genotypic value for the mean of individual birth weight and a genotypic value for the environmental variance. This new "trait" was modelled in the usual infinitesimal framework, giving estimated breeding values for environmental variability. There was a favourable selection response with a significant difference in within-litter standard deviation of birth weight between the lines selected for increasing (HOM) or decreasing (HET) homogeneity. At the end of the third generation, 31 females from the HOM line and 33 from the HET line were sacrificed to collect the uterine horns and measure their initial length (L1) and their length after elongation with a weight of 50 g (L2) and then 70 g (L3). The length in the homogeneous line was significantly greater, whatever the weight (L1: + 1.3 cm, P = 0.02; L2: + 2.8 cm P b 0.001; L3: + 4.2 cm, P b 0.001). The absolute and the relative elongations were significantly higher in the HOM line. There was no significant effect of the line on the number of ova shed, the weight of the ovary, or the weight of the uterine horns. It is concluded that the divergence between lines for the within-litter homogeneity of birth weight is at least partly due to the characteristics of the genital tract, i.e. the length and capacity for elongation of the uterine horn.

Breeding for robustness: the role of cortisol

“…Sensitivity to the environment may also contribute to the environmental variance of a trait, which has been shown to be under genetic control (SanCristobal-Gaudy et al, 2001;Sorensen and Waagepetersen, 2003;Ros et al, 2004;Mulder et al, 2007 and2008;Mulder et al, 2009). The reduction of trait variance by genetic selection is also known as canalizing selection or canalization (SanCristobal-Gaudy et al, 1998;Bolet et al, 2007;Garreau et al, 2008;Bodin et al, 2010).…”

Estimation of genetic variation in residual variance in female and male broiler chickens

“…Rowe et al (2006) used a two-step approach, in which the first stage used a model to analyze body weight with allowance for differences in residual variance among sire families, and in the second stage the variation among these estimates of the residual variance were analyzed with least squares. In some studies, log transformed squared residuals have been analyzed, also using a two-step approach (Larzul et al, 2006;Bolet et al, 2007), which gives the flexibility to account for environmental effects on the residual variance at the level of the record that is not possible in the least squares analysis of Rowe et al (2006). Ideally, one would simultaneously fit a model for the mean of the trait (e.g.…”

Genetic parameters related to environmental variability of weight traits in a selection experiment for weight gain in mice; signs of correlated canalised response

“…Likewise, several studies relate the weight gain to fertility and prolificacy [11,26]. Moreover, unequal growth of contemporary animals creates a competition that results in differential mortality [2,25].…”

“…Some selection experiments involving livestock species have been designed and are being carried out [2] to reach this goal, but, in order to reduce the generation interval, selection experiments with laboratory mammals are necessary [14].…”