Estimation of genetic parameters and trend of somatic cell score trait using test day records in Iranian Holstein cows

The objective of this research was to estimate the genetic parameters and trend of somatic cell count in Holstein cows of Iran using test day records. The phenotypic the used data consisted of were consisting of 407167 first lactation test day records the which were collected by the center of Animal Breeding and Livestock Production Improvement center of Iran during 2009 to 2013. Somatic cell count was transformed to Somatic cell score using logarithm transformation method. The genetic parameters were estimated using random regression models with Bayesian statistical method based on Gibbs sampling. The results revealed that the observed trend for additive genetic variance and permanent environmental were similar high in early lactation compared to other days. The heritability was estimated between 0.023-0.065 for somatic cell score. Repeatability showed highest changes at the start and the end of lactation. Additive genetic correlations were estimated for days 5 and 305. The result showed high variation in genetic trend of somatic cell score in different years, without an specific trend.