Variation due to additive, dominance and imprinting genetic effects in body weight gain of Baluchi sheep

Abstract

The aim was to estimate relative contribution of additive, dominance and imprinting genetic effects to the phenotypic variation of body weight gain in different growth phases, namely from birth to weaning (BWGa), weaning to 9 months of age (BWGb) and weaning to 12 months of age (BWGc) in Baluchi sheep. This was done in a two-step process. In the first step, each trait was analysed with 12 different animal models which included different combinations of additive genetic, dominance genetic and maternal effects. The best model (Model I) was selected with Akaike Information Criterion (AIC). In the second step, three additional models were fitted by adding maternal imprinting, paternal imprinting, or both (models 13–15) to the Model I. Predictive ability of models was measured using the mean squared error of prediction (MSE) and Pearson's correlation coefficient between the real and predicted values of observations (r($y$,$\hat{y}$)). Correlations between traits were estimated using bi-variate analyses. In the first step, for all traits studied, including dominance genetic effects in the model resulted to a significantly better data fit and enhanced predictive ability of the model (higher r($y$,$\hat{y}$) and lower MSE). Also it resulted to a significant decrease in the residual variance up to 24 %. However, accounting for dominance genetic effects, significantly increased the computing time and required memory. In the second step, for BWGa, adding maternal imprinting effects to the model I resulted to increase in the likelihood and predictive ability of the model as well as 40 % decrease in the additive genetic variance. Estimates of dominance heritability ($h_d^2$), were 0.19, 0.15 and 0.20 for BWGa, BWGb and BWGc, respectively. Additive heritability ($h_a^2$), were 0.08, 0.08 and 0.07 for BWGa, BWGb and BWGc, respectively. For BWGa, maternal imprinting heritability ($h_{\mathrm{mi}}^2$) was 0.08. While additive genetic correlations were all positive and high, dominance genetic correlation between BWGb and BWGc was positively high and between other pairs of traits was negatively high. For all traits studied, correlation between breeding values obtained from models with/without dominance genetic effect was close to unity (0.99) but between breeding values obtained from models with/without imprinting effects deviated from unity (0.85 for BWGa) indicating change in ranking of top animals across models. It was concluded that dominance and imprinting effects needed to be included in the genetic evaluation models for genetic evaluation of growth-related traits in Baluchi lambs.