Genetic and phenotypic analysis of reproductive traits in the Murciano-Granadina does: Predictive ability of the statistical models and estimation of genetic parameters

Abstract

In the present study, data collected between 2016 and 2022 from a private dairy farm of the Murciano-Granadina goat breed, in Ghale-Ganj city, located in the southern area of Kerman province, Iran was used for model comparison and estimation of genetic parameters for reproductive performance. Studied reproductive traits included litter size at birth per doe kidding (LSB), litter size at weaning per doe kidding (LSW), total litter weight at birth per doe kidding (TLWB), and total litter weight at weaning per doe kidding (TLWW). Four univariate animal models comprising various combinations of direct additive genetic, animal permanent environmental, and service sires effects were fitted for each trait. The predictive ability of models was evaluated by applying the predictive ability measure including the mean square of error (MSE) and the Pearson's correlation coefficient between observed and predicted values (r(y,y ̂)) through a two-fold cross-validation study. For LSW, TLWB, and TLWW, the model with direct additive genetic, animal permanent environmental, and service sires effects had the lowest MSE and the highest values for r(y,y ̂) than other models. For LSB, the model included direct additive genetic and animal permanent environmental was identified as the best model among the tested models. The posterior means for heritability estimates of the studied traits were low values of 0.02 ± 0.01, 0.07 ± 0.01, 0.02 ± 0.01, and 0.03 ± 0.01 for LSB, LSW, TLWB, and TLWW, respectively. The posterior means for repeatability estimates were 0.04 ± 0.01, 0.08 ± 0.02, 0.03 ± 0.01, and 0.04 ± 0.01 for LSB, LSW, TLWB, and TLWW, respectively. The posterior means for the ratio of service sires variance to phenotypic variance (S2) for LSW, TLWB, and TLWW were 0.09 ± 0.02, 0.02 ± 0.01, and 0.02 ± 0.01, respectively. Genetic correlation estimates were high in magnitude and ranged from 0.69 ± 0.09 (LSB-TLWW) to 0.97 ± 0.02 (LSB-LSW). Phenotypic correlations were low to medium estimates and ranged from 0.17 ± 0.01 (TLWB-TLWW) to 0.55 ± 0.02 (LSB-LSW). Because of low heritability estimates for the studied reproductive traits in the Murciano-Granadina goat breed genetic progress resulting from direct genetic selection for these traits is likely to be slow and improvement in environmental conditions is of great importance for improving the reproductive performance. No genetic and phenotypic antagonism were found among the studied traits. Therefore, it should be possible to simultaneously improve these traits.