برآورد فراسنجه‌های ژنتیکی و روند ژنتیکی امتیاز سلول‌های سوماتیک در گاوهای هلشتاین ایران

The objectives of present study were to estimate the genetic and permanent environmental covariance components and genetic and phenotypic trends of test-day records of somatic cell score (SCS) of the first lactation Iranian Holstein cows. Dataset included the 108995 test day records were collected by the Animal Breeding Center of Iran from 2001 to 2010. The GLM procedure of SAS software was used for fitting the fixed effects in the statistical models of analysis. All analyses were performed using the AIREML algorithm of WOMBAT software. 16 different random regression models were studied and compared based on Akaike’s information criterion. Random regression model with Legendre polynomial functions of orders of 4, 4, 5 were chosen to fit fixed regression, additive genetic and permanent environmental effects, respectively, and residual variance was assumed in 4 heterogeneous levels during the lactation. Estimation of heritability was low (0.022 to 0.032) that indicated this trait mostly affected by environmental factors. Genetic and environmental correlations between daily SCS were high for adjacent tests and low between the beginning and the end of lactation. The estimated environmental correlations were lower than the genetic correlations in all stages of lactation. Annual genetic and phenotypic trends were -0.59±0.103 and -0.08±0.002, respectively, for SCS trait. Both genetic and phenotypic trends for SCS were significant (P<0.0001). Negative genetic and phenotypic trends for SCS indicated that genetic programs for declining the incidence of mastitis in Iranian Holsteins were successful at recent years.