Potential of Somatic Cell Concentration in Milk as a Sire Selection Criterion to Reduce Mastitis in Dairy Cattle

Abstract

Lactation records for somatic cell counts in milk, bacteriological culture results, antibiotic treatment for mastitis, and production were formed for cows in 30 cooperating dairy herds in Virginia. A second data set, including somatic cell counts and production information for cows in approximatley 400 herds in Virginia (not including the original 30), was used to evaluate sires genetically for somatic cell count.Approximate genetic correlations between measures of cell count and measures of infection ranged from .36 to .67. These were highest (lowest) for frequency of infection by major (minor) pathogens. Corresponding phenotypic correlations were similar but slightly smaller. Neither somatic cell counts nor measures of infection were well correlated with treatment. Production traits generally had small, negative genetic and phenotypic relationships with cell counts, rates of infection, and measures of treatment.Correlations for evaluations of sires for cell count were positive with daughter averages for infection rates (.20 to .38) and treatment measures (.02 to .13). Largest (absolute value) correlations between evaluations of sires for cell count and production traits were for fat percentage (−.38) and fat yield (−.28). Evaluation and selection of sires for decreased somatic cell count may augment management and treatment programs in the reduction of mastitis incidence.