The estimation of genetic parameters of somatic cell scores in Murciano-Granadina goats using random regression models

In the present study, ۷,۰۸۹ test-day records on milk somatic cell counts (SCC) belonging to ۲,۴۳۲ first-parity Murciana-Granadina does in Kerman province were used. Test-day SCC records were transformed into milk somatic cell scores (SCS) and analyzed by applying random regression models (RRM) with the Legendre polynomials (LEG) function with order of ۲ to ۵ for additive genetic and permanent environmental effects and heterogeneous residual variances. The models were compared using the Akaike's information (AIC) and Bayesian information (BIC) criteria. The model with orders ۳ and ۲ for additive genetic and permanent environmental effects (RRM-LEG۳۲), respectively, was the best for genetic analysis of test-day SCS. The estimates of heritability (  and the ratio of permanent environmental variance to phenotypic variance ( ) for test-day SCS using the RRM-LEG۳۲ were low. They ranged from ۰.۰۳ at days in milk (DIM) ۱۵۵ and ۲۱۵ to ۰.۱۱ at DIM ۳۵ for  and from ۰.۰۱ at DIM ۶۵ to ۰.۱۴ at DIM ۲۷۵ for  estimates. Genetic correlation estimates among test-day SCS at ۵, ۷۰, ۱۳۷, ۲۰۳, and ۲۷۵ DIM were lower than the corresponding phenotypic correlations. Genetic correlation estimates ranged from ۰.۳۶ between DIM ۱۳۷ and DIM ۲۷۵ to ۰.۹۷ between DIM ۷۰ and DIM ۱۳۷ while the phenotypic correlations ranged from ۰.۰۳ between DIM ۷۰ and DIM ۲۰۳ to ۰.۰۹ between DIM ۵ and DIM ۲۰۳. In general, the strongest genetic correlations were found between closely located DIMs, with these correlations decreasing as the interval between DIMs increased. The low heritability estimates for test-day SCS records implied that they are mainly controlled by the non-additive genetic and environmental effects, limiting the efficiency of direct genetic selection for improving the test-day SCS. Therefore, including these effects in designing an appropriate breeding program for improvement in Murciano-Granadina goat udder health is of great importance.

کلیدواژه ها:

animal model ، genetic parameters ، Legendre polynomials ، somatic cell count ، test-day record