genetic and phonotypic trends for somatic cell score and determination of effective environmental factors on this trait in iranian holstein cows

the aim of this study was to estimate the genetic and phonotypic trends of somatic cell score in iranian holstein cows. also, the environmental factors affecting this trait are investigated. a total of 375351 test day records of somatic cells take from 54374 animals between year 2002 and 2007 were used in this study. the breeding values were estimated by fitting animal model in asreml software. genetic and phonotypic trends were estimated by regression of phonotype and breeding value means on year of calving. sas software was used for estimation of genetic, phonotypic trends and effect of environmental factors. the heritability, genetic and phonotypic trends for somatic cell score were 0.082 ± 0.009, 0.013 ± 0.002 and -0.224 ± 0.103, respectively. the genetic trend was significant and different from zero but phonotypic trends were not significant. effects of herd, year, interactions between herd and year, herd and season, year and season of calving were also significant however the effects of season of calving were not.