Polymorphism screening and association study of CXCR1 with udder health in dairy heifers

Similar to other countries, heifer mastitis is highly prevalent in Belgium. Marker assisted genetic selection against certain disadvantageous genotypes could offer possibilities to enhance host resistance. The main objective of this study was to screen CXCR1 for polymorphisms and to analyze their association with udder health during first lactation. This potential candidate gene encodes the homonymous receptor binding interleukin 8, a crucial chemokine in the innate immunity of the mammary gland. Eighty-six heifers originating from 20 Belgian farms were genotyped for the entire coding region. Fifteen single nucleotide polymorphisms (SNPs) were detected of which 10 have not been described before. Four distinct haplotypes were detected. The association between SNP at position +735 relative to the start codon (c.735C>G) and subclinical mastitis which has already been reported by other research groups could not be confirmed in our study. Instead, SNP c.642G>A was found to be associated with udder health. Prevalence of intramammary infection (IMI) in early lactation was significantly lower in heifers expressing genotype AA compared to heifers expressing genotype AG or GG. Additionally, SNP c.982A>G tended to be associated with pathogen group specific IMI. Heifers with genotype GG on this locus were more susceptible specifically to major pathogens compared to those expressing genotype AG or AA. Numerical differences in somatic cell count in early lactation and throughout lactation by CXCR1 genotype were observed but were not statistically significant. Results in this study are promising and stimulate to further elucidate the role of CXCR1 in mastitis susceptibility.