Ovarian response in mares to prolonged treatment with exogenous equine pituitary gonadotrophins

Twelve anoestrous mares were treated with an intravaginal sponge containing 0.5 g allyl trembolone (Regumate; Roussel UCLAF, Paris) and 50 mg oestradiol benzoate for 7 days, followed by daily intramuscular (i.m.) injections of 25 mg crude equine pituitary extract (CEG), with (n = 6) or without (n = 6) 0.25 mg porcine growth hormone (pGH). No difference in ovarian response to this superovulation treatment was observed between the 2 groups (2.2 +/- 0.4 vs 2.3 +/- 0.4 ovulations per mare, respectively). CEG treatment was then combined with allyl trembolone (40 mg per os per day) and prolonged in the 12 mares, with (n = 6) or without (n = 6) a 7-day interruption of CEG treatment 7 days after the mares first ovulated. Ovarian responses showed that an interruption in gonadotrophin treatment was not necessary to allow the occurrence of a new follicular wave, but the interruption did seem to generate the growth of a more synchronous cohort of follicles. Ovulation rate in the second wave was higher than in the first although there was no effect of treatment interruption on ovulation rate in the second wave, which occurred during progestagen treatment and gave rise to persistent corpora lutea (36.5 +/- 5.9 days). The 6 mares that did not experience an interruption in treatment continued to receive daily CEG injections and oral progestagen. Two periods (Days 0-47 and Days 48-94) were compared for analysis of follicular growth.(ABSTRACT TRUNCATED AT 250 WORDS)