The objective of this study was estimation of variance - covariance component for somatic cell score (LSCS, the lactation mean of the natural log of test- day somatic cell count) of Iranian Holstein across parities. Test day of somatic cell count for first, second and third parity that collected from 1993 to 2010 by Animal Breeding Center of Iran, were used. Each LSCS in the parity was considered as separate trait. Multi trait analysis was performed by ASReml software. Mean of LSCS for first, second and third parity was 7.78, 8.22 and 8.47. The heritability estimates for parities varied form 0.05 - 0.09. Genetic correlations between parities were higher than 0.90 but environmental correlations between parities were in range of 0.11 to 0.21. Genetic correlations between parity demonstrate that genes that control LSCS in parities are same and selection animal for LSCS in first parity would have affected LSCS in other parity

Keywords