ABSTRACT We conducted research to evaluate whether ergot alkaloids associated with endophyte-infected tall fescue could alter plasma concentrations of hormones important to reproductive function in cows. Six primiparous, estrous-cycling Holstein cows nursing calves received single i.v. injections of ergotamine tartrate, ergonovine maleate, or saline vehicle in a simple cross-over design. Each cow received one compound per estrous cycle, d 15 or 16 after estrus, and all compounds over three estrous cycles. Blood samples were collected at 20-min intervals for 40 min before and 240 min after treatments to assess plasma concentrations of prolactin, LH, FSH, and the response by PGF2alpha metabolite 13,14-dihydro-15-keto-prostaglandin F2alpha (PGFM). Ambient temperature and respiratory rates were measured hourly. Ambient temperature averaged 26oC during data collection. Treatment x time was a significant source of variation for respiration rate and plasma concentrations of every hormone evaluated except FSH. Ergotamine elevated (P < .01) respiration rates 2 to 4 h after treatment. Ergotamine and ergonovine reduced (P < .001) plasma concentrations of prolactin for 2 to 4 h after treatment compared to concentrations before treatment. Plasma concentrations of LH were lowered (P < .01) by ergonovine during the 3rd h after treatment and by ergotamine during the 4th h after treatment. Most cows exhibited secretory PGFM responses after ergotamine and ergonovine treatments compared with an absence of a PGFM response in all cows after saline (P <= .01). Results indicated that ergot alkaloids implicated as causative agents for fescue toxicosis can alter plasma concentrations of reproductive hormones during the late luteal phase of the estrous cycle in cows.
IMPLICATIONS Acute exposure to ergot alkaloids altered plasma concentrations of luteinizing hormone and prostaglandin F2alpha metabolite in cows. It should be recognized that cows grazing endophytic fescue experience chronic exposure to numerous alkaloids. Nevertheless, these results showed that ergot alkaloids associated with N. coenophialum can affect concentrations of hormones that regulate bovine reproductive function. Reproductive efficiency of the cow herd is of utmost economic importance to cattle producers. Reduced plasma luteinizing hormone and increased prostaglandin F2alpha concentrations during the late luteal phase of the estrous cycle as induced by ergot alkaloids suggest that modified endocrine function may be one reason consumption of endophyte-infected tall fescue hinders bovine reproduction.
Key Words: Cattle, Ergot Alkaloids, Prolactin, LH, Prostaglandins, Festuca Poisoning
© 1998, by the American Society of Animal Science. All rights reserved.
J. Anim. Sci. 1998. 76:1448-1454 Back to Table of Contents