Folliculogenesis and Ovulation in Equine Species

Abstract

The hypothalamus is considered as a key point of reproductive control; this organ produces the GnRH hormone, a decapeptide that is released into the hypothalamic-pituitary portal system to stimulate the synthesis and release of gonadotropins. Gonadotropins are responsible for ovarian follicular dynamics, estrogen production, ovulation and luteinization of the corpus luteum, as well as other hormones and substances such as the insulin-like growth factor (IGF-1), and the Pregnancy-associated plasma protein A (PAPPA), which control the main signs of estrus behavior and the events that determine ovulation. Some of the most significant ovulation processes include the release of the follicular prostaglandin that starts the lysis of the follicle wall; this lysis is associated to the increase of the endothelial nitric oxide synthase (eNOS), which increases ovarian blood flow by activating the vasoactive peptide angiotensin II (Ang II), endothelin-1 (ET-1) and atrial natriuretic peptide (ANP). This review aims to increase awareness of the events related to the estrous cycle, follicular dynamics and the ovulation process so as to apply them properly to the management of reproduction in mares.