Embryo Mobility
When performing ultrasonography before day 17 it is essential to see transuterine movement of the embryo. This occurs between both uterine horns and the uterine body. Mobility of the embryo begins to slow by day 15 and completely stops by day 17. The mobility of the embryo is essential for early recognition of pregnancy. The embryo is secreting a substance which will prevent the uterus from releasing the hormone PGF2a. Remember that PGF2a is released around day 17 of the estrous cycle to cause the normal regression of the corpus luteum in a non-pregnant mare. The substance from the embryo must come in contact with all surfaces of the uterine endometrial linning. Inhibition of transuterine mobility results in failure of the mare to recognize she is pregnant and production of PGF2a by parts of the uterine endometrium. The PGF2a would then cause regression of the corpus luteum, the mare would come into estrus, the uterine environment would not be compatible with embryo survival and any potential embryo would die.
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