Foal Losses: View From the Field

Actually, the view from the field in Central Kentucky was rather lonely this Thursday, May 10. There were acres and acres of fresh-mown--or being furiously mowed--pastures that are beginning to resemble putting greens. The recommendation is to cut the grass to hopefully reduce the amount of mycotoxins being ingested by mares--if in fact that is the cause of the current syndromes affecting pregnant mares. Managers and owners desperate for something to do that might help were taking all suggestions seriously. Veterinarians were pulling out all the stops treating at-risk mares with everything that seems logical. Researchers and scientists were busily taking samples and running tests to try and find answers.

During this interim from outbreak to answer, many farms are keeping in-foal mares in stalls. While this might solve the problem of keeping them off the pasture, it brings about other problems. Many of these pregnant mares have healthy foals which would be much better off outside getting exercise. The answer to that is either turn out the pregnant mares with the foals--which most managers aren't going to do--or wean the foal--another unacceptable scenario. Therefore, some farms are hand-walking mares and foals morning and afternoon, and spending a lot more time cleaning stalls.

Dr. Roger Murphy, president of the Kentucky Veterinary Medical Association and the Kentucky Association of Equine Practitioners, said he thinks the measures he and other vets are taking are working to some degree. He believes that mares less than 50 days pregnant which are treated medically (mostly with domperidone and progesterone) and taken off pasture are showing some signs of reversal of the problems.

In one mare he scanned with ultrasound Thursday, a few days ago her pregnancy was "going downhill." The fetus had a high heartrate (greater than 120 beats per minute, which is a sign of stress), there was a "folding" along the edges of the vesicle that contained the fetus, and there were particles in the fluid surrounding the fetus. On Thursday, the fluid was clear, the fetal heartrate was normal, and the vesicle containing the fetus looked smoother.

Another mare which was suffering the same symptoms a few days ago only got worse. Murphy told the farm manager that her placenta was thickened, the fetus had a high heart rate, and there were particles in the fluid of the vesicle surrounding the fetus. While the foal was still alive, the vet didn't hold out much hope for the mare remaining pregnant.

And so the story went at farm after farm--good news and bad news. One farm lost no foals and all the mares remained pregnant. One farm reported very few 2001-crop foals lost, but about a 70% loss in early pregnancies. Another farm had three normal foals born this last week.

It seems that mares are getting in foal easily, then at 45-50 days are starting to show signs of problems. With the current medical treatments, mowing, and a little rain, it is hoped that if this was an environmental anomaly, then perhaps Mother Nature will tender the cure. Murphy said that mares over 50 days pregnant which lose the fetus are tough to get back in foal because endometrial cups have already begun to form. This physical circumstance makes it more difficult to get mares to return to a normal cycle.

In his practice, Murphy said he has seen about a three-fold increase in fetal loss. "On average, you see about 10-12% early fetal loss in any given year. The average this year has been about 38% in my practice." For foals, the average loss for any given year is about 4-5%. This year Murphy thinks the loss will be about 10% of late-gestation foals in his practice.

Some other observations from the field that might or might not be related to the current syndromes of foal loss:

* Managers and vets are seeing unexplained fevers in yearlings and foals. This brings up the question of whether the mycotoxin in the grass (if it is the cause) could have an effect on growing horses--specifically on the growth plates.

* Veterinarian Murphy remarked that he has seen more large foals at foaling this year than in any other single foaling season. (Some of them have been born at 160 pounds.)

* Mares which lost early fetuses are coming back into heat and are re-breeding successfully.

* For this entire breeding season, Murphy said he has seen an unusual amount of mares getting in foal on only one cover. ("Fertility has been astonishing this year.")

* An incinerator is needed at the Kentucky Disease Diagnostic Center to resolve the problem of too many carcasses waiting to be taken to the rendering plant after necropsy and remove the potential of spreading a future disease if one occurs that is contagious from horse to horse (unlike the current situation, where the problem does not seem to be contagious).