Association of CXCR2 polymorphisms with subclinical and clinical mastitis in dairy cattle

The ability to identify objectively cows that are more or less susceptible to mastitis has been a long-standing goal. Genetic markers associated with inflammatory responses during mastitis could aid in selection of these cattle. One potential marker is CXCR2, a chemokine receptor required for neutrophil migration to infection sites, which contains single nucleotide polymorphisms (SNP) within the gene. The objective of this experiment was to evaluate the association of CXCR2 SNP genotypes with subclinical and clinical mastitis. Thirty-seven Holstein and 42 Jersey cows that completed at least 2 full lactations were used. Quarter foremilk samples were collected for bacteriological examination quarterly and when cows exhibited clinical mastitis. Subclinical mastitis was defined as the presence of the same pathogen in the same quarter in at least 2 of 3 consecutive samples. A significant association was detected between CXCR2 SNP +777 genotype and percentages of subclinical mastitis cases in Holsteins. Holsteins expressing genotype GG had decreased percentages of subclinical mastitis, but genotype CC cows had increased percentages of subclinical mastitis. Significant differences in clinical mastitis incidence were not detected between genotypes for either breed. This approach of genetically identifying mastitis resistant cows may represent an effective means of marker-assisted selection for mastitis and other inflammatory diseases involving neutrophils.