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Bayesian inference on genetic parameters for some reproductive traits in sheep using linear and threshold models

Yadollahi, Sakine, Gholizadeh, Mohsen, Hafezian, Hasan
Small ruminant research 2019 v.170 pp. 149-153
Bayesian theory, breeding, computer software, genetic correlation, heritability, linear models, litter size, litter weight, phenotypic correlation, reproductive traits, sheep, threshold models, variance, weaning
Genetic parameters for reproductive traits in Baluchi sheep were estimated on 3844 dams born during 1991 to 2012. The studied traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB), litter mean weight per lamb weaned (LMWLW), total litter weight at birth (TLWB) and total litter weight at weaning (TLWW). Significant effects were determined using Logistic and GLM procedure of SAS software for threshold and continuous traits, respectively. Variance components needed for breeding were estimated using Gibbs sampling methodology of Bayesian inference. The genetic parameters for LMWLB, LMWLW, TLWB TLWW were estimated by fitting a linear model. To examine the appropriateness of fitting linear or threshold model to litter size at birth and weaning, both models were used to estimate genetic parameters on the observed data. Posterior means of the heritabilities of litter size at birth and weaning by using a threshold model were estimated to be two times higher than the heritabilities based on the linear model (0.18 versus 0.09 and 0.11 versus 0.05 for LSB and LSW, respectively). Bayesian information criterion (BIC) selected the threshold model as most appropriate model for LSB and LSW given the data. The heritability estimates for LMWLB, LMWLW, TLWB TLWW resulting from linear analysis were 0.12, 0.05, 0.06 and 0.08, respectively. Genetic correlation estimates between the traits ranged from −0.67 for LMWLB–TLWW to 0.85 for LSB–TLWB. Phenotypic correlations ranged from −0.06 for LSB–LMWLW to 0.88 for LSB–TLWB and permanent environmental correlations ranged from −0.74 for LMWLB - TLWW to 0.88 for LSB–TLWB. Results of this study showed that the threshold model seems to be reliable for genetic evaluation of litter size in Baluchi sheep.