ارسلان برازنده

In the present study, 7,089 test-day records of milk somatic cell count (SCC) of 2,432 first-parity Murciana-Granadina does, which were collected from 2017 to 2024 at a private dairy farm located in Ghale-Ganj city, in the southern region of Kerman province, Iran 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 2 to 5 for additive genetic and permanent environmental effects and heterogenous residual variances. The investigated models were compared using Akaike's information criterion (AIC) and Bayesian information criterion (BIC). The model with orders 3 and 2 for additive genetic and permanent environmental effects (RRM-LEG32), respectively, was the best for genetic analysis of test-day SCS. The estimates of heritability (h^2) and the ratio of permanent environmental variance to phenotypic variance (〖pe〗^2) for test-day SCS using the RRM-LEG32 were low. They ranged from 0.03 at days in milk (DIM) 155 and 215 to 0.11 at DIM 35 for h^2 and from 0.01 at DIM 65 to 0.14 at DIM 275 for 〖pe〗^2 estimates. Genetic correlation estimates among test-day SCS at DIMs 5, 70, 137, 203, and 275 were lower than the corresponding phenotypic correlations. Genetic correlation estimates ranged from 0.36 between DIM 137 and DIM 275 to 0.97 between DIM 70 and DIM 137 while the phenotypic correlations ranged from 0.03 between DIM 70 and DIM 203 to 0.09 between DIM 5 and DIM 203. In general, the highest genetic correlations were observed between nearby DIMs and decreased as DIMs got further apart. The low heritability estimates for test-day SCS records implied that they are mainly controlled by non-additive genetic and environmental effects which limits the efficiency of direct genetic selection for improving test-day SCS. Therefore, including these effects in designing an appropriate breeding program for improving the udder health in the Murciano-Granadina goat breed is of great importance.