Embryo transfer in anovulatory recipient mares

Abstract

This article discusses the main aspects of using hormonal protocols based on the application of estrogen followed by progestogen in anovulatory or acyclic recipients, either in anestrous or transition in embryo transfer protocols. Most mares demonstrate seasonally polyestrous behavior, by which they manifest estrus and ovulatory cycles during periods of higher daily luminosity. The annual reproductive cycle of mares is characterized by the presence of four phases defined by follicular dynamics: anestrous, spring transition, ovulatory, and autumn transition. During the phases of transition and anestrous, the incidence of ovulations decreases or is zero, making it difficult to synchronize ovulations between donors and recipients in preparation for embryo transfer. Some studies have shown that anovulatory/acyclic recipient mares managed with steroid-based protocols have similar uterine changes to those observed in pregnant mares. However, there is no sufficient research to allow to clarify the best steroid protocol with respect to dose, treatment times, and routes of administration.