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Association of CXCR1 Gene Polymorphisms with Incidence Rate of Clinical Mastitis, Somatic Cell Count and Milk Production in Dairy Cattle
The objective of this study was to analyze associations between single nucleotide polymorphisms (SNPs) in the CXCR1 gene (NCBI Gene ID: 100125580), potential genetic markers for mastitis resistance, and the incidence rate of clinical mastitis (IRCM), test-day somatic cell count (SCC) and test-day milk production (MP). Clinical mastitis was monitored on 50 randomly selected Flemish dairy herds for a period of 1 yr. Each case was sampled and cultured according to NMC (National Mastitis Council) guidelines. Incidence rate of clinical mastitis (cases/days at risk) was calculated independently of the culture results and for Staphylococcus aureus, Streptococcus uberis, Streptococcus dysgalactiae, and Escherichia coli, separately. Dairy herd improvement records including SCC and MP were available on 32 herds. A fluorescent multiprobe PCR assay was designed to genotype simultaneously SNP CXCR1c.735C>G (rs208795699) and SNP CXCR1c.980A>G (rs43323012). In total, 3107 cows were genotyped. Associations between the SNP and (pathogen-specific) IRCM were analyzed using mixed Poisson regression models. Linear mixed regression models were fit to test associations between the SNP and SCC and MP. In total, 681 CM samples were analyzed with S. uberis (23% of the culture positive samples), E. coli (20%), S. aureus (10%), and S. dysgalactiae (9%) being the most frequently isolated pathogens. Both SNPs were significantly associated with MP (P < 0.05) but not with (pathogen specific) IRCM or SCC. Milk production was higher in c.735GG cows (28.6 kg/day, n = 571) compared to c.735CG (28.1 kg/day, n = 1043) and c.735CC (28.0 kg/day, n = 516) cows. Additionally, MP was higher in c.980GG cows (28.4 kg/day, n = 1277) compared to c.980AG cows (27.9 kg/day, n = 743). In conclusion, SNP CXCR1c.735C>G and CXCR1c.980A>G were not associated with the studied udder health traits but were with test-day MP.
Keywords: CXCR1 genotype, udder health, milk production