Fetomaternal interactions and influences during equine pregnancy

Area of Science:

• Reproductive biology
• Endocrinology
• Veterinary science

Background:

• The equine embryo undergoes a 6-day oviductal journey before entering the uterus.
• Maternal recognition of pregnancy occurs around day 17 via embryonic signals to the endometrium.

Purpose of the Study:

• To detail the developmental timeline and hormonal contributions of the equine placenta and fetus during pregnancy.
• To explain the formation and function of equine endometrial cups and their role in early pregnancy maintenance.

Main Methods:

• The study is based on observational data and established knowledge of equine reproductive physiology.
• Analysis of embryonic and fetal development, placental formation, and hormonal profiles throughout gestation.

Main Results:

• Equine endometrial cups form between days 25-38, secreting eCG to stimulate accessory corpora lutea for progesterone production.
• The allantochorion develops by days 80-85, establishing a microcotyledonary structure for fetal nutrition by days 120-140.
• The fetoplacental unit synthesizes steroid hormones, utilizing fetal precursors for estrogens and maternal precursors for progestagens.

Conclusions:

• Endometrial cups and eCG are crucial for maintaining early pregnancy in mares until placental independence.
• The equine placenta provides essential nutrition and synthesizes significant amounts of steroid hormones in late gestation.
• Unusual hormonal profiles near term, with increasing progestagens and decreasing estrogens, are characteristic of mares.