We have a 16 yr old APHA broodmare that foaled in January. We had her ultrasounded on day 31 (would have liked to start earlier, but vet was unavailable). SHe had just ovulated, so we ran to the stud farm and picked up semen. She was inseminated 6 hrs later. We started ultrasounding for pregnancy at day 14 and were unable to find a pregnancy. She has been checked every other day and is now at day 23. Her uterus is toned, she is not building any significant follicles (several 10-15mm) and is not teasing to the stallion. We did find what we thought could be a vesicle in the upper uterine horn adjacent to the oviduct. The vesicle (if that is what it is) is only 14mm. Regardless, this mare thinks she is pregnant. If this is a pregnancy, it certainly does not look normal.
Are we better off to just prostin this mare and start over? I know she will get her endometrial cups soon and then really take awhile to be ready to breed. What dosage do you recommend?
If it is a vesicle, it should be down by the corpus-cornual junction by now, but I'd give a it a day or two to sort itself out before doing anything radical. Day 28 post-ovulation is the latest day recommended to do anything, and if you are seeing a pregnancy from a second - later - ovulation, it may not yet be at the point of fixture.
A standard luteolytic dose of Prostaglandin F2α is all that is required to cause a mare to return to estrus.
Thank you Jos. Another question... If this is not a vesicle, why would the mare not have returned to estrus? Do mares have false pregnancies? And if this IS a vesicle, and it does not move, is that dangerous?
Thanks so much for your time, it is great to have you as a resource!
If the mare was pregnant (but the object you are seeing was perhaps a cyst not a vesicle) but underwent early embryonic death, it could delay the return to estrus.
If it is a vesicle, then it's not exactly dangerous, but if the mare has really gone past the point of fixation (around 16 days - and with a diameter of 14mm I'm a little skeptical that she has if it's a vesicle, as that would be small), it doesn't bode well for the pregnancy as upper horn or body pregnancies are usually doomed in the horse...
Check it again and see it is growing or moving - and remember that by day 23 a heartbeat should be visible per ultrasound if it is a pregnancy.
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