Exploring polymorphisms and effects on milk traits of the DGAT1, SCD1 and GHR genes in four cattle breeds

One hundred seven cattles of four breeds (Holstein–Friesian, Jersey, Valdostana and Piedmontese) were genotyped at the DGAT1 K232A and the SCD1 A293V variants, as well as at 7 SNPs of the GHR gene, that were used to construct 14 GHR haplotypes. Allele frequency at most SNPs, and GHR haplotype frequencies highly differed between breeds. The effect of each SNP and haplotype was associated to milk production traits. The consistent effect of the 232K allele of DGAT1 on the increase of fat and protein content was confirmed in the Holstein and the Jersey, while this allele is missing in the Valdostana and rare (0.03) in the Piedmontese. SCD1 A293V variant showed no effect on either milk yield or fat and protein content. The positive effect of GHR F279Y variant on milk fat and protein content, although much weaker than the effect of DGAT1, was confirmed. The combination of the GHR SNPs into haplotypes seems to improve the association, likely for the interaction of variant F279Y with a SNP in the GHR gene promoter.