I had my mare ultrasounded yesterday at 23 days since last breeding. The vet said the pregnancy is in the uterine body. I know she can't carry the foal to term, so heres my questions. I read that sometime the embryo moves from horn to horn, can this embryo just be moving, is there a possibility of it implanting in a horn in the near future? When should I be expecting her to abort (the vet said very soon)? Should I just terminate the pregnancy now and start over? Is this likely to happen again, ie. mares that have uterine body pregnancies can have them more frequently than typical mares? Thanks!
Fixation of the conceptus usually occurs around day 16 post-ovulation. There could be a few days delay in rare cases, but it would be unlikely that there would be a 7 day delay. It does seem likely therefore that the pregnancy is indeed permanently in the body if that's where your vet found it.
Not all body pregnancies will terminate - some may go to term - but an extremely high percentage will be lost. This loss may occur at any stage, but certainly when placentation is initiated, one will start to see a higher loss rate as there is not an adequate nutrient transfer.
Presuming that semen from the stallion is easily available, termination of the pregnancy is recommended, and soon. Not only does one have to consider that attempting to maintain the body pregnancy is likely to end in loss, but also if that loss occurs after the endometrial cups form and eCG hormone levels rise, one is not going to see the mare come back into estrus before those cups regress and levels subside - typically 3-5 months - and that is going to blow the rest of the breeding season for you. It is therefore recommended to terminate if you choose that route, no later than 28 days (i.e. within the next few days) to avoid eCG secretion. Prior to that though, I would recommend another ultrasound to absolutely rule out the possibility that the conceptus has moved again to a more favourable position.
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