Date of Award
Master of Science
An abstract of the thesis of Casie S. Bass, for the Masters of Science degree in Animal Science, presented on April 7, 2010 at Southern Illinois University Carbondale. TITLE: CABERGOLINE EFFECTS ON MARE ESTROUS BEHAVIOR, CYCLICITY, AND ENDOCRINE PROFILES MAJOR PROFESSOR: DR. SHERYL S. KING Adding to the seasonal reproductive perplexity in the mare, many researchers support the idea that multiple controllers may "drive" this event, including both hormonal and neural regulators. Evidence supports the theory that dopamine can exert direct action on the equine ovary independent of prolactin (Jeffcoate, 1993; King et al., 2005). Operating on the hypothesis that dopamine causes direct inhibitory actions within the mare ovary, the present investigation was designed to examine the ovarian, hormonal, and reproductive behavior responses to longterm stimulation of dopamine D2 receptors on the cycling ovary. We hypothesized that the dopamine agonist, cabergoline, would induce a autumnal transitional-like ovarian function in summer cycling mares. More specifically, cabergoline-treated mares would express decreased circulating prolactin, decreased luteal progesterone levels, slowed follicular growth leading to longer estrous cycles, an increased incidence of luteolytic failure resulting in spontaneous prolonged corpora lutea, and possibly a decrease in the intensity of estrous behavior. Cabergoline, a dopamine agonist, was administered orally to cycling mares during the peak breeding season. Reproductive behavior, ovarian and cervical activity, and endocrine profiles were assessed. Results from the present study demonstrated a suppression of prolactin after cabergoline administration, a unique ambivalent effect that dopamine appears to exert on sexual behavior, and a possible suppression-effect during diestrous follicle development in the mare.
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