Gestation in the mare. Part I.

Gestation in the mare presents unique characteristics that distinguish it from other domestic species. After fertilization in the oviduct, the embryo reaches the uterus between days 5.5–6.5 post-ovulation, where a glycoprotein capsule unique to equids is formed, providing it with sphericity and protection. The embryonic vesicle undergoes extensive uterine mobility until day 16, a mechanism essential for maternal recognition of pregnancy and prevention of luteolysis. From days 36–38, endometrial cups form and secrete equine chorionic gonadotropin (eCG), stimulating the development of accessory corpora lutea. The placenta is of a diffuse epitheliochorial type, and the source of progestagens progressively transitions from the ovary to the fetoplacental unit, which will be the primary source from day
100 onwards. Pregnancy diagnosis can be performed using laboratory methods (progesterone, eCG, estrogens, relaxin) and, more frequently, clinical methods (rectal palpation, transrectal ultrasonography).