A SINGLE NUCLEOTIDE POLYMORPHISM IN THE DOPAMINE RECEPTOR D2 GENE MAY BE INFORMATIVE FOR RESISTANCE TO FESCUE TOXICOSIS IN ANGUS-BASED CATTLE

Fescue toxicosis (FT) reduces beef animal growth and fertility. Animals afflicted with FT typically have decreased circulating prolactin concentrations and thicker summer hair coats. Preliminary experiments examined the informativeness of a novel Dopamine Receptor 2 (DRD2) G/A SNP for resistance to FT. Steers grazed tall fescue containing a toxic (E+) or non-toxic (NTE) strain of endophyte. Decreased serum prolactin concentrations were observed in GG steers in May compared to AA steers when grazing E+ pastures (P<0.02). In a second study, GG steers had decreased prolactin concentrations (P=0.004) and increased hair coat scores (P=0.01) relative to AA steers when grazing E+ pastures. Allele and genotypic frequencies were different (P=0.016 and 0.026, respectively) between spring-calving and fall-calving herds grazing E+ pastures, such that the A allele and the AA genotype were more prevalent in spring-calving herds, suggesting active selection for the A allele. Regardless of calving season, AA heifers tended toward fewer days to first calf (733.6 +/- 4.4 d) than did GG heifers (756.6 +/- 9.2 days; P=0.055). These results suggest that the DRD2 SNP may have use in selecting animals resistant to FT.