Polymorhpisms at DRD2 Gene Affect the Gains of Cow-Calf Pairs on Tall Fescue Pasture.

Tall fescue (Lolium arundinaceum Schreb.) toxicosis results from livestock consuming forage infected with wild-type strains of Neotyphodium coenophialum Morgan-Jones & Gams. This disease costs livestock producers nearly $1 billion annually through reduced animal gains and poor reproductive success. A single nucleotide polymorphism recently discovered on the dopamine receptor D2 (DRD2) gene provides a prospective test that could be used to develop lines of beef cattle tolerant to toxic tall fescue. The objective was to determine the response of beef cattle genotyped as either homozygous for adenine (A) or guanine (G) on the DRD2 gene when grazing either toxic endophyte-infected ‘Kentucky-31’ (KY-31) or novel endophyte-infected ‘BarOptima Plus E34’ (BO+) tall fescue (2x2 factorial). Five cow-calf pairs were rotationally grazed on each of the different tall fescue-endophyte associations which were replicated three times (n=30 cow-calf pairs each year). Body mass of cows and calves was collected along with pasture nutritive value, ergovaline concentrations, and forage accumulation data. As expected, the ergovaline concentration of KY-31 tall fescue was greater than for BO+. Our data show that cows of the AA genotype and grazing KY-31 raised calves with 25 kg hd^-1 greater 205d adjusted weaning weights (P=0.03) than GG cows on the same forage. Cow genotype had no influence (P=0.99) on 205d adjusted weaning weight of calves when BO+ was the forage, though the weaning weights were 18 to 42 kg hd^-1 greater than for either genotype grazing KY-31. These data show that producers who are unable to renovate KY-31 fields could use cows of the AA genotype to partly offset the impact of tall fescue toxicosis.