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Onset of the winter anovulatory period in mares is associated with a marked diminution in adenohypophyseal synthesis and release of LH. Native GnRH, unlike its synthetic agonists, stimulates the synthesis and secretion of LH in mares without pituitary refractoriness. Herein we tested the hypotheses that (1) the average Julian day of pregnancy can be accelerated by up to 2 months in winter anovulatory mares treated continuously with native GnRH beginning on February 1 and (2) mares will sustain luteal function and pregnancy after treatment withdrawal. Forty-two winter anovulatory mares were stratified by age, body condition score, and size of the largest follicle across two locations in a randomized design and assigned to one of three groups (n = 14 per group): (1) Control: untreated, (2) GnRH-14: GnRH delivered subcutaneously in saline at a rate of 100 μg/h for 8 weeks (February 1–March 29) using four …