REPRODUCTIVE HORMONAL RESPONSES TO ERGOTAMINE AND ERGONOVINE IN COWS DURING THE LUTEAL-PHASE OF THE ESTROUS-CYCLE

We conducted research to evaluate whether ergot alkaloids associated w ith endophyte-infected tall fescue could alter plasma concentrations o f hormones important to reproductive function in cows. Six primiparous , estrous-cycling Holstein cows nursing calves received single i.v. in jections of ergotamine tartrate, ergonovine maleate, or saline vehicle in a simple cross-over design. Each cow received one compound per est rous cycle, d 15 or 16 after estrus, and all compounds over three estr ous cycles. Blood samples were collected at 20-min intervals for 40 mi n before and 240 min after treatments to assess plasma concentrations- of prolactin, LH, FSH, and the response by PGF(2 alpha), metabolite 13 , 14-dihydro-15-keto-prostaglandin F-2 alpha (PGFM). Ambient temperatu re and respiratory rates were measured hourly. Ambient temperature ave raged 26 degrees C during data collection. Treatment x time was a sign ificant source of variation for respiration rate and plasma concentrat ions of every hormone evaluated except FSH. Ergotamine elevated (P < . 01) respiration rates 2 to 4 h after treatment. Ergotamine and ergonov ine reduced (P < .001) plasma concentrations of prolactin for 2 to 4 h after treatment compared to concentrations before treatment. Plasma c oncentrations of LM were lowered (P < .01) by ergonovine during the 3r d h after treatment and by ergotamine during the 4th h after treatment . Most cows exhibited secretory PGFM responses after ergotamine and er gonovine treatments compared with an absence of a PGFM response in all cows after saline (P less than or equal to .01). Results indicated th at ergot alkaloids implicated as causative agents for fescue toxicosis can alter plasma concentrations of reproductive hormones during the l ate luteal phase of the estrous cycle in cows.