Genetic parameters for test day somatic cell count in Italian Holstein Friesian cows

Somatic cell count has been proposed as a selection criterion to slow increases in mastitis incidence resulting from current breeding schemes aimed to improve milk production traits. Aims of this paper are: 1) to estimate genetic parameters for somatic cell count in first parity Italian Holstein Friesian cows, treating test day observations as different traits within lactation; 2) to evaluate the effect of different data sampling strategies on the estimates of genetic parameters; 3) to estimate genetic correlations between somatic cell count and milk traits within day of test. A total of 672,193 test day records collected between 1989 and 1996 on 106,462 first parity cows in the northern Italy were available for the analysis. Different sampling strategies were applied to extract records from the whole data file for the estimation of genetic parameters. Sampling strategies were: random sampling of herds, random sampling of herds keeping lactation records with a minimum number of test day records within the lactation; random sampling of herds larger than a given size. The analysis has been carried out using a multiple trait REML Animal Model procedure. Results are discussed.