Ergovaline levels in tall fescue and its effect on performance of lactating cows

To investigate the effects of ergovaline on milk production of lactating dairy cows, a survey and feeding trial were conducted. In the survey, 25 samples of imported tall fescue (Festuca arundinacea) hay were collected and analyzed for ergovaline. Ergovaline was detected in all 25 samples, ranging from 21 to 782 μg/kg, and averaging 125 μg/kg (dry matter (DM) basis). Based on a toxic threshold ergovaline level of 50 μg/kg DM, more than one-half of the samples could be potentially toxic to cattle. In the feeding trial, 12 Holstein dairy cows were fed one of two diets for 28 days. A total mixed ration (TMR; concentrate:roughage ratio of 0.54:0.46, DM basis) with tall fescue hay (450 g/kg of dietary DM) contained either a low (45 μg/kg DM; LE) or high level of ergovaline (782 μg/kg DM; HE). Temperature ranged from −0.1 to 13.1 °C. Intake of TMR and tall fescue, and milk yield were not different between treatments. Milk fat content (P<0.001) and milk fat yield (P<0.05) for HE were lower than for LE. Milk protein concentration was lower (P<0.05) for HE than for LE, but lactose concentration was not different. Solids-not-fat concentration for HE was lower (P<0.001) than for LE due to decreased milk fat and protein concentrations. These results indicate that feeding HE tall fescue can reduce performance of lactating dairy cows even with relatively cool temperatures and a relatively high dietary ratio of concentrate to roughage.