Estimation of Genetic Parameters for Litter Size and Growth Traits in a Prolific Line of Tunisian Barbarine Sheep

Abstract

This study aimed to assess genetic parameters for ewe productivity in a Tunisian Barbarine sheep line. The traits studied were litter size (LS), birth weight (BW), weight at 90 days (W90), and average daily gain between 10 and 30 days (ADG13). A total of 3804 growth and 2726 lambing records were used. Bivariate linear and threshold animal models were fitted and analyzed using the Gibbs sampling methodology. Heritabilities for LS obtained with univariate threshold, bivariate linear, and threshold models were around 0.15, higher than the estimate obtained by a univariate linear model (0.09 ± 0.03). Direct heritability for growth traits remained consistent across models, except for W90 in the bivariate linear threshold model. Maternal heritability for growth traits was higher than direct heritability, ranging from 0.07 to 0.15, except for BW. The covariances between the direct and maternal effects of growth traits were slightly negative. Repeatability oscillated between 0.16 and 0.62. Direct genetic correlations between LS and the other traits were negative, varying from −0.18 (LS-BW) to −0.83 (LS-W90). Our results suggest that the threshold model may be the most appropriate for LS. A selection index including LS and growth traits may be proposed for routine genetic evaluation in this population.

Keywords

• litter size
• growth
• genetic parameters
• bivariate model
• threshold
• Gibbs sampling