Conclusion Of the sixteen polymorphisms in seven immune related genes genotyped, only CXCR1-777 tended to associate with SCS albeit only in the on-farm study. Interestingly polymorphisms in the immune genes, CXCR1, CD14, SERPINA1, did associate with milk composition. Ani- mals with the GCGGC SERPINA1 haplotype associated with superior genetic merit for milk protein yield and fat percentage. The lack of an association between the polymorphisms with SCS in the Holstein-Friesian data set would question the potential importance of these variants in selection for improved mastitis resistance in the Holstein-Friesian cow.