PROGESTERONE AND ESTRADIOL IN BIODEGRADABLE MICROSPHERES FOR CONTROL OF ESTRUS AND OVULATION IN MARES

Progesterone and estradiol 17-beta in poly (DL-lactide) microspheres w ere used to control estrus and ovulation in mares after luteolysis was induced by prostaglandin F2 is-proportional-to Mares were given a sin gle intramuscular injection of biodegradable poly (DL-lactide) microsp heres, 1 day following prostaglandin treatment, containing no hormones (control), 0.625 g progesterone and 50 mg estradiol (low dose), 1.25 g progesterone and 100 mg estradiol (medium dose), or 1.875 g progeste rone and 150 mg estradiol (high dose; n=15 mares per group). Mares tre ated with the low dose had significantly longer intervals (P<0.05) to estrus and ovulation than the control mares; however, low dose mares h ad shorter intervals (P<0.05) to estrus than high dose mares and short er intervals to ovulation than medium and high dose mares. Regression analysis indicated that the medium dose was sufficient for maximizing interval to ovulation while the high dose maximized interval to estrus . All groups of mares exhibited similar (P>0.05) post-treatment estrus lengths. A clinical response scoring system based on synchrony of bot h estrus and ovulation within a treatment group was also used to measu re the effectiveness of treatments on control of estrus and ovulation. Clinical response scores did not differ (P>0.05) among treatment grou ps. Mares were randomly assigned for insemination at the beginning of the first post-treatment estrus. Rates for embryo recovery performed b y uterine lavage 7 days post-ovulation did not differ (P>0.05) among g roups. Concentrations of serum progesterone increased in mares receivi ng progesterone and estradiol microspheres. At 10 to 14 days post-inje ction of microspheres, progesterone concentrations were higher (P<0.05 ) and remained above 1 ng/ml in the mares receiving the high dose. Pro gesterone concentrations were also higher (P<0.05) on Days -3 to -1 (D ay 0 = day of post-treatment ovulation) in mares receiving the high do se when compared to control mares. Gonadotropin concentrations were su ppressed (P<0.05) in the medium and high dose groups.