08/17/2001 12:00AM

Pregnant mares monitored in study of foal death syndrome


LEXINGTON, Ky. - Months after at least 1,200 central Kentucky mares lost their fetuses in the mysterious mare reproductive loss syndrome of April and May, some researchers are monitoring pregnant mares to determine whether or not their fetuses are growing normally.

At a veterinary symposium hosted in Saratoga Springs, N.Y., by Cornell University and the New York Thoroughbred Breeders, reproductive veterinarians noted that the cause of MRLS remains unidentified, and they discussed concerns that fetuses that survived the epidemic might encounter developmental problems.

Dr. Walter Zent of Lexington's Hagyard-Davidson-McGee equine hospital told participants that the clinic is working with the Gluck Equine Research Center to study 100 mares who were bred around March 15, the breeding window for many MRLS-affected mares, but ones who did not abort their fetuses.

"Hopefully, we can learn whether their fetuses are growing pretty normally," he said. "We are measuring the areas of the fetus that we can see - the eye, the diameter of the aorta, the femur, the diameter of the chest. Essentially, we measure the growth. The idea is to learn something about the fetal growth, and, hopefully, if the fetuses continue to grow normally, people will be less worried about these mares."

The study group involves about 100 mares who live year-round on eight central Kentucky farms. Zent said the criteria required the mares to be 15 or younger and bred on or before March 15. The fetuses are measured once a month, and, just two months into the study, Zent said that the fetuses measured so far are normal.

A team headed by Dr. Dietrich Volkmann of Cornell has proposed another research project to study the hormonal patterns in mares affected by the syndrome. Volkmann noted that veterinary accounts of the syndrome provide evidence that placental development and function may have been among the first things affected by the syndrome. But not all mares showing abnormal fetal fluid lost their foals.

"This raises the question as to whether fetuses that were not aborted are developing well and normally," he said, adding that a mare's hormone levels can serve as indicators of placental health. "We may be able to predict whether placental function in partially affected individuals returned to normal or remained affected for longer periods of time. That may assist us in predicting the outcome of affected but surviving pregnancies: will such foals be normal or abnormal at birth?"

The cause of MRLS is still unknown, but researchers are investigating a number of theories, ranging from cyanide and hemlock poisoning to possible increased potassium concentrations or mycotoxins in pastures. A panel of veterinarians at the symposium said that most feed now includes mycotoxin binders, which neutralizes the mycotoxins' effect, and that there appears to be no downside to feeding those. Most of the participants also agreed that there is little indication for medicating mares with domperidone, a preventive treatment for fescue toxicosis. But with so little known about the syndrome's cause, the panelists agreed that definitive recommendations will depend on continuing research.

OCD disease on the decline

Also at the symposium, Dr. Alan Nixon of Cornell discussed a bone problem that breeders and trainers often deal with in horses: the developmental the orthopedic disease osteochondrosis dessicans, a common joint disability in which cartilage detaches from bone and begins to disintegrate.

Nixon pointed out that research has identified a link between diet and OCD, and that horsemen's increased awareness of that has caused a significant decrease in OCD incidence.

"The most prominent dietary difference on farms with a low incidence of OCD was a diet higher in copper and zinc," Nixon said. "Follow-up feeding trials have further demonstrated that both copper and zinc play an important role in the development of OCD."

Nixon noted that research suggests that other dietary factors, such as excessive protein and energy levels, also may influence OCD by increasing a young horse's growth rate. Genetics may also be involved.

"Studies of Kentucky yearlings in the 1980's showed that nutritional changes dramatically lowered the incidence of OCD, but then the incidence on each farm studied reached a constant level, suggesting another cause. That is now believed to be genetic. But environmental factors are probably more important than genetics."

Nixon said that OCD, which affects twice as many colts as fillies, can be treated by therapies ranging from reduced exercise to joint injections to surgery.