Genetic parameters for clinical mastitis, somatic cell counts, and milk production estimated by multiple-trait restricted maximum likelihood.

Heritabilities and genetic correlations for mastitis, SCC, and milk production in first lactation were calculated using data from the Swedish disease recording system. Genetic parameters were estimated from sire components of variance and covariance obtained from a multiple-trait restricted maximum likelihood procedure. Data were stratified into three subsets according to breed and AI stud. The numbers of cows were 46,431, 25,373, and 25,201, respectively. Heritabilities of mastitis and SCC averaged .014 and .080, but breed differences were seen. Genetic correlations between mastitis and SCC were moderately high, averaging .6. Milk production showed a slightly unfavorable genetic correlation with mastitis and SCC.