Pregnancy:
* Estrogen: Plays a crucial role in early pregnancy. It helps establish and maintain the uterus lining (endometrium), prepares the mare's body for conception, and suppresses ovulation.
* Progesterone: The "pregnancy hormone," produced by the corpus luteum (a temporary structure on the ovary) and later by the placenta. Progesterone maintains the pregnancy by keeping the uterine lining thick and preventing contractions, ensuring the fetus stays implanted.
* Human Chorionic Gonadotropin (hCG): This hormone is produced by the early embryo and helps to maintain the corpus luteum, ensuring a continued supply of progesterone.
* Equine Chorionic Gonadotropin (eCG): Unique to horses, this hormone is produced by the early placenta and acts like LH, promoting the development of additional corpora lutea on the ovary. This provides a higher concentration of progesterone, crucial for successful pregnancy.
Foaling:
* Prostaglandin F2 Alpha (PGF2a): This hormone, produced by the uterus, is responsible for initiating the cascade of events that lead to foaling. It causes the corpus luteum to regress, reducing progesterone levels and allowing estrogen levels to rise.
* Estrogen: As progesterone decreases, estrogen rises, initiating the final stages of gestation. It increases uterine contractions and relaxes the cervix, preparing for delivery.
* Oxytocin: This hormone is released from the pituitary gland and plays a crucial role in the final stages of labor. It triggers strong uterine contractions, facilitating the expulsion of the foal.
* Relaxin: Produced by the placenta, relaxin softens the ligaments and joints of the pelvis, allowing the mare to expand her birth canal and deliver the foal.
Other Important Hormones:
* Adrenocorticotropic hormone (ACTH): Produced by the pituitary gland, ACTH stimulates the adrenal glands to release cortisol, which plays a role in maintaining pregnancy and preparing the mare for labor.
* Cortisol: This hormone is essential for maintaining the pregnancy and contributing to the final stages of labor.
Note: These are just some of the key hormones involved. Other hormones like prolactin, insulin, and thyroid hormones also play indirect roles in pregnancy and foaling.
Understanding these hormones is crucial for managing a mare's pregnancy and ensuring a healthy foaling.