EFFECT OF ERGOTAMINE AND ERGONOVINE ON PLASMA-CONCENTRATIONS OF THYROID-HORMONES AND CORTISOL IN CATTLE

Plasma samples from two experiments were processed to determine whethe r ergot alkaloids associated with endophyte-infected tall fescue alter ed peripheral thyroxine (T-4), triiodothyronine (T-3), or cortisol con centrations in cattle. In Exp. 1, seven Angus steers (294 kg) received i.v. bolus injections of saline (SAL), ergonovine maleate (7 mg; EM), or ergotamine tartrate (7 mg; ET) at weekly intervals, and they recei ved all treatments during the study. Blood was sampled every 15 min fo r 5 h, and treatments were given after h 1. Mean ambient temperature w as 34 degrees C. Treatment x time affected plasma concentrations of T- 3 (P < .05) and of cortisol (P < .001) but not that of T-4 (P > .2). P lasma T-3 concentrations were not affected by SAL, whereas concentrati ons increased (P < .01) after either EM or ET treatment. Plasma cortis ol concentrations were not altered by SAL or EM, but they were increas ed (P < .001) by ET treatment. In Exp. 2, six Holstein cows (499 kg) n ursing calves received a bolus i.v. injection of SAL, EM (9.5 mg), or ET (9.5 mg) per estrous cycle, and all treatments were given over thre e cycles. Blood was sampled every 20 min for 5 h; treatments were give n after h 1. Mean ambient temperature was 26 degrees C. Treatment x ti me affected T-3 (P = .08) and cortisol (P < .001) and tended to influe nce (P = .16) T-4 concentrations. Plasma T-3, T-4, and cortisol concen trations were not influenced by SAL treatment. Plasma T-3 was higher ( P less than or equal to .01) after EM or ET treatment compared with pr etreatment concentrations. Concentrations of T-4 during the 4 h after EM and ET were increased (P < .001) compared with pretreatment. Plasma cortisol concentrations were not altered by EM hut were increased (P < .001) by ET. Ergot alkaloids implicated as contributing agents to fe scue toxicosis alter plasma concentrations of hormones important to me tabolic and thermoregulatory functions in cattle.