EVALUATION OF A DOSING METHOD FOR STUDYING ERGONOVINE EFFECTS IN CATTLE

We evaluated the feasibility of using miniosmotic pumps as a way to co ntinuously treat cattle with a singular ergot alkaloid (ergonovine) of known content, thus mimicking the natural fescue toxicosis disease st ate, but allowing study of specific alkaloid effects. Dosing animals w ith increasing amounts of ergonovine via miniosmotic pumps, followed b y daily acquisition of plasma samples for high-performance liquid chro matographic determination of the alkaloid, resulted in stepwise increa ses in plasma ergonovine concentration. However, despite the detectabl e blood concentration of ergonovine, calves did not have typical clini cal signs of ergot alkaloid toxicosis. Similarly, serum prolactin conc entration was unaffected by ergonovine in these cattle, implicating so me other alkaloid of endophyte-infested fescue as causative of the usu al prolactin-suppressive response. The results confirm use of this ani mal dosing method to study biological effects of singular purified alk aloids of known amount, without bioavailability concerns. Thus, this d osing method will facilitate studies to determine the harmful effects of individual alkaloids found in toxic tall fescue, and ultimately, to alleviate their costly effects in cattle, horses, and other species.