genetic and phenotypic analysis for somatic cell score in iranian holstein dairy cattle

the objective of this study was to estimate variance components, genetic and phenotypic trends for somatic cell score. dataset that collected by the animal breeding center of iran was used in this study. data file included 850,729 test day records of somatic cell counts (scc)  on 32,955 cows from lactations one to four, in 472 herds, gathered from years 2002 to 2013 in iran. a test day repeatability animal model was used to estimate the genetic parameters and variance components using asreml. the heritability was estimated 0.176. estimated repeatability (± se) for within (rwit) and between (racr) parities were 0.362 ± 0.006 and 0.230 ± 0.002, respectively. the genetic and phenotypic trend based on regression of average breeding values of scs on year of birth, was -0.0246 and -0.047, respectively. this trend could be due to genetic improvement and mastitis management control programs that are widely being used across the dairy farms in country.