Dr. Tom Riddle: One Practitioner's Experience With Foal Loss Problem

I have been asked to speak about my experience with the recent early fetal loss syndrome in Central Kentucky. I saw my first two cases on April 26 when I was asked to fetal sex six mares on a farm in Jessamine County. Fetal sexing requires the use of ultrasound in mares between 60 and 70 days of gestation. Of the six mares which I ultrasounded on that farm, two had dead fetuses surrounded by allantoic fluid which was filled with echogenic particles. Both of these mares felt pregnant based on rectal palpation. It was very unusual to find two dead fetuses on the same day on the same farm. Last year I estimate that I found only five dead fetuses out of 400 mares which I fetal sexed during the entire year. After finding the two dead fetuses on the farm, I contacted the farm veterinarian and we assumed it was just extremely bad luck.

The following day, April 27, I fetal sexed six mares on a farm in Woodford County and again found two with non-viable fetuses surrounded by a very cloudy fluid. I reported to the farm manager and the farm's veterinarian that I had had a similar experience the day before and that I was concerned that the cases might be related.

Three days later, on April 30, I found a dead fetus in a mare in Bourbon County. At that point, I was very concerned. I talked with the Jessamine County farm veterinarian and he had found several more mares with either dead fetuses or with live fetuses surrounded by a cloudy fluid. This veterinarian and I began asking other veterinarians if they had seen similar cases. At this point, April 30, no one we talked to had seen this early fetal loss.

On May 1, after finding three more cases I contacted Dr. Neil Williams at the Diagnostic Laboratory to let him know we would be sending fetuses and serums from these mares, and I contacted Dr. Roberta Dwyer at the Gluck Center to report the alarming numbers of early fetal deaths on multiple farms. Unfortunately, since that time I have seen many more cases, as have most veterinarians in Central Kentucky.

In my practice, I have noticed no effect on conception rates in mares checked 15 days from breeding. There appears to be no effect on the normal pregnancy loss rate between 15 and 28 days.

I have seen 23% of pregnancies lost between 28 and 42 days and a 30% loss between 42 and 60 days.

By far the largest number of cases is in the 60-85 day range with 35% found to have aborted by that time period, with another 32% showing abnormal allantoic fluid.

Detecting the Problem

While the majority of mares present with no outward signs, some mares present with a vulvar discharge ranging from a dark brown serous material to outright pus. A few mares have presented with membranes hanging from their vulvas. I have had one mare reported to have shown signs of straining prior to aborting, but otherwise no one has reported any behavioral changes.
I have not had fever reported to me in any cases, although I have heard another practitioner report fever in one mare.

While many of the mares have been found to palpate pregnant, only to find a dead fetus on ultrasound, some mares have less fluid distention of the uterus on rectal examination and others have completely eliminated the fetus and are obviously not pregnant.

Ultrasound examination of the typical case reveals a fetus which is approximately normal in size to slightly small with no heartbeat. The allantoic fluid is generally filled with a "snowstorm" of echogenic material.

In some cases the fetus is still alive and is surrounded by fluid containing varying amounts of material. In 2 cases, only the amniotic fluid was cloudy, with the allantoic fluid clear. I have followed some fetuses for 6 days that continue to live in spite of obviously abnormal allantoic fluid. I will continue to follow these to monitor viability of the fetus.

I have checked several mares that looked perfectly normal on ultrasound, only to find that they have aborted 3 to 4 days later.

Measurement of the thickness of the chorio-allantois or placenta may be helpful in predicting future viability of the fetus, although I have not done enough to make a definitive statement.

Unfortunately, the majority of these mares which abort after 40 days will not return to ovulatory heats until approximately 120 days after their last breeding date. While the mare may show signs of heat and produce a follicle, the follicle will almost always luteinize or form a corpus luteum instead of ovulating. On initial examination of the post-abortion mare who is showing signs of heat, she may have a normal appearing follicle; however, because the follicle is under the influence of the endometrial cups which begin formation at approximately 36 days, the follicle will not ovulate but will instead develop flocculence within the fluid as it becomes a corpus luteum. The endometrial cups are naturally eliminated by the body between 90 and 120 days post conception, therefore most mares will not begin cycling normally until approximately 120 days post breeding. Mares that return to normal ovulating heats prior to that time will be the exception.

In 23 years of practice in Central Kentucky I have seen only one episode of early fetal loss that was similar to our current situation. This occurred in 1981 on multiple farms in Central Kentucky. This was prior to the use of ultrasound so we were limited to rectal palpation to confirm the pregnancy status of mares. There were large numbers of mares between 60 and 90 days of gestation who were found to have aborted. Comparable to our current situation, some mares were found with membranes protruding from the vulva with the fetus lying in the reproductive tract. In 1981, the abortions were limited to mares bred in February through mid to late March. Mares bred from April on were not affected. No definite cause was ever found for that outbreak.

Possible Management Solutions

It is very difficult to make recommendations for practical management of our mares which are pregnant from this year's breedings because we do not know the cause of the abortions.

It is reasonable to me to assume that the cause of the problem is in the pastures where the mares are grazing; therefore, anything we can do to reduce grazing could be helpful.

Ideally, removing the mares from the pasture would be the best way to avoid possible exposure to a toxin. Practically speaking, this would be extremely difficult to manage. I have clients who are mowing their fields very closely and I have one client who has plowed a field and essentially eliminated all grazing.
We, as horsemen, know that there are many complications that can arise from complete stall confinement for a mare, especially if she has a foal by her side. This option would have to be considered a last resort.

It is very difficult to make a reasonable recommendation for medical management of mares with apparently healthy fetuses since we do not know the cause of the problem. I have measured progesterone levels in a number of mares that have aborted and have found them to be well within the normal range to maintain a pregnancy. Therefore I am not recommending that mares be supplemented with progesterone or Regu-mate.

Because the later term stillborns show some signs that are consistent with an endophyte toxicity, I think it is reasonable to assume that the cause of the early fetal loss could be related. For that reason, I have recommended to my clients that they consider the use of Domperidone in their pregnant mares. This product was designed for use in late term mares and there has been no research to my knowledge that shows that it would have any efficacy in preventing early fetal loss. But, we are in a situation in which we are trying to do everything possible to prevent pregnancy loss and I feel that Domperidone could be helpful. Researchers that I have talked with feel that there should be no harm from using it. Another possible avenue for preventative treatment is a feed additive containing a Brewer's yeast – like mixture and Saccharomyces Cerevisiae fermentation solubles. These substances may be helpful if the mare is ingesting a mycotoxin.

I have also recommended that my clients place their pregnant mares on Banamine for 5 days until we have a better idea of the cause of the abortions. Banamine is a potent anti-inflammatory and is known to fight endotoxins and this is my rationale for it's use.

While we have likely ruled out bacterial infection as a cause of our problem, I have recommended that my clients place their mares on sulfa-trimethoprim in case there is a secondary bacterial infection.

In closing, I want to stress the necessity of using ultrasound to determine fetal viability. After 75-80 days, it becomes more difficult to image the fetus and we will have to rely more on the appearance of the fluid and the size of the uterine distention.

About the Author

Tom Riddle, DVM

Tom Riddle, DVM is a founding partner of Rood and Riddle Equine Hospital in Lexington, Ky.

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