Toxicity of endophyte-infected ryegrass hay containing high ergovaline level in lactating ewes
Résumé
The symbiotic association of Epichloe festucae var. lolii (formerly named Neotyphodium lolii) with perennial ryegrass (Lolium perenne) leads to the production of ergovaline (EV) and lolitrem B (LB) that are toxic for livestock. The objectives of this study were to determine the effects of feeding endophyte-infected ryegrass (SE+) hay on 16 lactating ewes (BW 80 +/- 10 kg) in comparison with endophyte-free ryegrass (SE-) hay to investigate the putative mechanisms of action of EV and LB and to evaluate their persistence in milk and animal tissues. The mean EV and LB concentrations in SE+ hay were 851 and 884 mu g/kg DM, respectively, whereas these alkaloids were below the limit of detection in SE-hay. No effect of SE+ was observed on animal health and skin temperature whereas prolactin decreased and significant differences between hays were observed from d 7 to 28 of the study (P < 0.03) but had no effect on milk production. Hematocrit and biochemical analyses of plasma revealed no significant difference between SE+ and SE-, whereas cortisol concentration differed significantly on d 28 (P = 0.001). Measurement of oxidative damage and antioxidant enzyme activities in plasma, liver, and kidneys revealed a slight increase in some enzyme activities involved in defense against oxidative damage in the SE+ fed ewes. Slight variations in the activities of hepatic and kidney flavin monooxygenase enzymes were observed, whereas in the kidney, glutathione S-transferase activity decreased significantly (P = 0.002) in the SE+ fed ewes, whereas uridine diphosphate glucuronosyltransferase activity increased (P = 0.001). After 28 d of exposure of ewes to the SE+ hay, low EV and LB concentrations were measured in tissues. The highest concentration of EV was observed in the liver (0.68 mu g/kg) whereas fat contained the highest concentration of LB (2.39 mu g/kg). Both toxins were also identified at the trace level in milk.