The Role of Light Progression in the Hormonal Sequence of the Mare’s Estrous Cycle
The hormone sequence of the mare’s estrous cycle is driven by the progression of increasing day length. The mare’s hormones are affected as the days get longer. This eventually brings her to estrous, and then to ovulation. In the mare’s estrous cycle, the initial hormones affected by increasing day length are the hypothalamic hormones, GnRH and kisspeptin. GnRH, a hormone that is produced by the hypothalamus and stimulates secretion by the pituitary (Munoz Cueto et. al. 2020). Another hypothalamic hormone is Kisspeptin. It acts in the hypothalamus and stimulates GnRH production (Zhao, et al. 2017,). This hormone cascade leads to a surge in LH, which is the primary hormone responsible for the mare’s receptiveness to breeding. The LH surge triggers the mare’s estrous cycle and leads to the ovulatory follicle becoming the dominant follicle in the ovary (Robinson et al., 2016). As the LH surge continues, the dominant follicle produces increasing amounts of progesterone, which is essential for the mare’s receptiveness to breeding.