THE EFFECTS OF PERPHENAZINE AND BROMOCRIPTINE ON FOLLICULAR DYNAMICS AND ENDOCRINE PROFILES IN ANESTROUS PONY MARES

Nineteen anestrous pony mares were used in a project designed to deter mine the effects of altered prolactin concentrations on follicular dyn amics and endocrine profiles during spring transition. The dopamine an tagonist, perphenazine, was administered daily to mares (0.375 mg/kg b ody weight) in Group A (n=6), while Group B mares (n=7) received 0.08 mg/kg metabolic weight (kg(75)) dopamine agonist, 2-bromo-ergocriptine , intramuscularly twice daily. Mares in Group C (n=6) received 0.08 mg /kg(75), im., saline twice daily. Treatment began January 20, 1994, an d continued until ovulation occurred. Mares were teased 3 times weekly with an intact stallion. The ovaries of the ponies were palpated and imaged weekly using an ultrasonic B-mode unit with a 5 Mhz intrarectal transducer until they either exhibited estrual behavior and had at le ast a 20-mm follicle, or had at least a 25-mm follicle with no signs o f estrus. At this time, ovaries were palpated and imaged 4 times weekl y. Blood samples were obtained immediately prior to ultrasonic imaging for measurement of prolactin, FSH and estradiol-17 beta. Perphenazine treatment advanced the spring transitional period and subsequent ovul ation by approximately 30d. Group A exhibited the onset of estrual beh avior earlier (P < 0.01) than control mares. In addition, Group A mare s developed large follicles (> 30 mm) earlier (P < 0.01) than Group B mares, with least square means for Groups A and B of 47.0 +/- 8.8 vs 8 8.1 +/- 8.2 d, respectively. Control mares developed 30-mm follicles i ntermediate to Groups A and B at 67.3 +/- 8.8 d. Bromocriptine decreas ed (P < 0.05) plasma prolactin levels throughout the study, while perp henazine had no significant overall effect. However, perphenazine trea tment did increase (P < 0.05) mean plasma prolactin concentrations fro m Day 31 to 60 of treatment. There were no differences in mean plasma FSH or estradiol-17 beta between treatment groups. We concluded that d aily perphenazine treatment hastened the growth of follicles and subse quent ovulation while bromocriptine treatment appeared to delay the gr owth of preovulatory size follicles without affecting the lime of ovul ation. (C) 1998 by Elsevier Science Inc.