LEXINGTON, Ky. - Although the number of sick and dying foals may be slowing, veterinarians are seeing other illnesses, including a potentially fatal heart condition, occurring in increased numbers in horses of all ages. Doctors are unsure if the growing number of cases of pericarditis, the development of fluid in the sac around the heart, seen in the past two to three weeks is connected to the recent outbreak of Mare Reproductive Loss Syndrome.

"I think the coincidence would imply that the two somehow are related," Dr. Doug Byars, internal medicine specialist at the Hagyard-Davidson-McGee clinic in Lexington, said Tuesday. "To see the number of cases we've seen in the past week to 10 days is profound and tells us we're dealing with another pattern of illness."

In the past three weeks, foals have been dying and mares losing fetuses at a staggering rate across central Kentucky. More than 6 percent of this year's foal crop and up to 25 percent of the 2002 foal crop may have been lost to the unexplained syndrome.

Scientists have not pinpointed a cause for the deaths, but they have focused their research efforts on possible mycotoxins produced by fungal organisms in pasture grasses and fescue endophyte toxicity.

Byars said he had seen about 45 cases of pericarditis in recent weeks, including eight on Friday, four on Saturday and three each on Sunday and Monday. Annually, the hospital might see three or four cases for the entire year, he said.

"It's certainly cause for alarm," Byars said.

The condition has been seen in horses of all ages, including suckling foals, yearlings and broodmares.

Dr. Bill Bernard, internal medicine specialist at Lexington's Rood and Riddle Equine Hospital in Lexington, said his hospital had seen eight pericarditis cases in the past two weeks.

"I'm not sure I'd characterize it as an epidemic, but we certainly have seen a huge increase in numbers," Bernard said. "It's very unusual."

Dr. Johanna Reimer, a cardiology specialist at Rood and Riddle, said the illness is characterized by inflammation and an influx of fluid in the sac around the heart.

Pressure caused by the swelling and fluid can make it difficult for blood to re-enter the heart and cause heart failure, she said.

"In severe cases, it can be fatal," Reimer said.

Treatment for the condition includes the draining of the fluid from around the heart and drug therapy, including antibiotics and steroids, Reimer said.

Doctors also have noticed higher than normal instances of fever, eye inflammation and laminitis, an inflammation of the sensitive laminae in the horses feet, which may or may not be related to the syndrome.

Meanwhile, both Byars and Bernard agreed that the number of dead or sickly foals at their hospitals and aborted early-term pregnancies on the farms appeared to be declining.

"They seem to be trickling off," Bernard said. "It may be because we've seen the worst of it or it may be because we're getting closer to the end of the breeding season. At this point, we're not sure."

Twenty-six dead foals -- 18 late-term and eight early-term -- were delivered to the University of Kentucky's Livestock Disease Diagnostic Center between Monday afternoon and Tuesday afternoon, bringing the total to 468 since April 28. Twelve were received at the center on both Sunday and Monday.

Last season, the center received fewer than 70 in the same period.

"I think the real barometer will be when broodmares stop having these early-term fetal losses," Byars said. "Until then, I don't think we can say for sure that this is over."