Genetic study of reproductive traits in Iranian native Ghezel sheep using Bayesian approach

The genetic parameters of reproductive traits in Iranian native Ghezel sheep were estimated using different univariate and bivariate animal models. For this research 4173 records of 2420 ewes, collected during 1992 to 2010 in breeding center of Ghezel sheep (Miandoab), were used. Significant effects were determined using Logistic and GLM procedure of SAS software for discrete and continuous traits, respectively. Genetic parameters were estimated for four basic and four composite traits using Gibbs sampling methodology of Bayesian inference. Basic traits were conception rate (CR), number of lambs born (NLB), number of lambs born alive (NLBA), number of lambs alive at weaning (NLAW) and composite traits were number of lambs born per ewe exposed (NLBEE), number of lambs at weaning per ewe exposed (NLWEE) total litter weight at birth per ewe lambing (TLBW), total litter weight at weaning per ewe lambing (TLWW). Based on Derivative Information Criteria (DIC), for each trait the most appropriate model was determined. Heritability estimates for direct genetic effect ranged from 0.032±0.01 for NLWEE to 0.196±0.01 for TLBW and for maternal genetic effect ranged from 0.023±0.01 for NLWEE to 0.074±0.02 for TLWW. Growth rate traits (TLBW and TLWW) had higher heritability than reproductive traits that may probably be due to non-normal distributions of reproductive traits and as well as little genetic variability for these traits. Genetic correlation estimates ranged from −0.39 for CR and NLBA to 0.91 for NLBA and NLBEE. Genetic correlations were usually more than phenotypic ones. Negative correlations may depend on distributions of the data in which CR is binary and others are not. Results of this study showed that the model with genetic correlation between direct and maternal effects seem to be reliable for genetic evaluation of reproductive traits in Ghezel sheep.