Evaluation of injectable sustained release progestin formulations for suppression of estrus and ovulation in mares.

摘要

Thirty-one mares were used in an experiment to evaluate the effectiveness of three sustained-release injectable formulations of altrenogest and one formulation of medroxyprogesterone acetate (MPA) for long-term suppression of estrus and ovulation. Luteolysis was induced by injection of prostaglandin-F_{2 alpha} (Lutalyse) on day 0 (6th day after the previous ovulation) and was immediately followed by treatment with (1) no injection (controls; n=7), (2) 1.5 mL of an altrenogest solution in sustained-release vehicle (LA 150, 1.5 mL; 225 mg altrenogest; n=6), (3) 3 mL (450 mg altrenogest) of the same solution (n=6), (4) 500 mg altrenogest in lactide-glycolide microparticles suspended in 7-mL vehicle (MP 500; n=6), or (5) 1.0 g MPA as a 5-mL suspension. Mares were checked for estrus daily, and their ovaries scanned every other day until a 25-mm or greater follicle was detected, after which they were scanned daily. Control mares returned to estrus an average of 3.9 days after Lutalyse administration; all the single-injection altrenogest formulations increased (P<.05) the days to return to estrus, with the greatest increase occurring in mares receiving MP 500. Return to estrus was not affected by MPA treatment. Time of ovulation was determined by serial ultrasound scans and confirmed by daily plasma luteinizing hormone (LH) and progesterone concentrations. Control mares ovulated an average of 8.8 days after Lutalyse administration. Treatment with 1.5 or 3 mL of LA 150 increased (P<.05) the mean days to ovulation to 16.5 and 21.2 days, respectively; MP 500 increased (P<.05) the days to ovulation to 33.5 days. Administration of MPA did not affect (P