Genetic and phenotypic parameters for individual cow somatic cell counts in Zimbabwean Holstein-Friesian cattle

Abstract. Genetic and phenotypic parameters for lactation average individual cow SCC in Holstein cattle were estimated. Records from the Zimbabwe Dairy Services Association included a total of 7912 lactation records, from which were 1453 first lactation, 2211 second lactation and 4248 third and later lactation records for the period 1994 to 1998. SCC were transformed through a base 2 logarithm. Genetic parameters were estimated with the AIREML Programme. A univariate mixed animal model was used to estimate heritabilities and repeatabilities. The heritability estimates for log₂SCC were 0.10, 0.12 and 0.14 for the respective first, second, third and subsequent lactations. Estimate of repeatability for log₂SCC was 0.17. Genetic and phenotypic correlations were estimated with a multivariate mixed animal model. Genetic correlation estimates between log₂SCC and the production traits were low to medium and negative (−0.05 to −0.55) whilst the phenotypic correlation estimates were low and negative (−0.04 to −0.22). As individual cow SCC data collection continues in Zimbabwe, there are opportunities for genetic re-evaluation of this trait with a larger data set. This could possibly include udder type traits, most of which have been reported to be associated with SCC.