347
Evaluation of a Commercial Genetic Test to Determine Tolerance to Fescue Toxicity in Beef Cattle
Tall fescue (Lolium arundinaceum Schreb.) is the most predominant forage used in Southeastern United States for cow-calf production. Endophyte-infected tall fescue is easily established, adaptable to different environments and grazing tolerant, however alkaloids produced by the fungus cause metabolic disorders in animals referred to fescue toxicosis. Previous research has demonstrated cows consuming endophyte-infected tall fescue have decreased prolactin concentrations, decreased milk production and reduced growth performance in stocker calves. Animals have been shown to differ in degree of tolerance to endophyte-infected tall fescue. T-Snip™ is a commercial genetic test developed to identify tolerance of cattle to toxic tall fescue. The objective of this study was to analyze correlation between T-Snip™ test in cows consuming endophyte-infected tall fescue and 205-day weaning weights of their respective calves. We hypothesized T-Snip™ test score would be predictive of 205-day weaning weights of calves from cows consuming endophyte-infected tall fescue. Nine herds, with four herds tested two or more years, consuming endophyte-infected tall fescue were tested for fescue toxicity tolerance using the T-Snip™ genetic test between years 2012 and 2015. Cows were scored from zero to five for tolerance to fescue toxicity with zero being intolerant and 5 being most tolerant. Total of 2494 tests were performed and number of animals per herd ranged from 75 to 647. Correlation coefficient between cow tolerance score and 205-day weaning weights were measured for each herd and year data set. Correlation from each data set was significant (P ≤ 0.02). The correlation coefficient averaged 0.63 and ranged from 0.42 to 0.76. Calf weaning weights from cows scored 0, 1, 2, 3, 4 and 5 averaged 212, 218, 226, 233, 240 and 246 kg respectively. In conclusion, T-Snip™ score from cows consuming endophyte-infected tall fescue was correlated to calf 205-day weaning weight and can be used as an indicator of tolerance to fescue toxicity. Difference in calf weaning weight between tolerant and intolerant cows averaged 28 kg. Tolerance to toxic tall fescue as determined by T-Snip™ analysis accounts for approximately one-half the effect of toxic tall fescue on calf weaning weight.
Keywords: beef cattle, fescue toxicity, tolerance test