LEXINGTON, Ky. - An abortion syndrome that has caused mares to abort late in pregnancy has killed 442 near-term fetuses and foals from April 28 through noon on Monday, according to figures released Monday by the University of Kentucky's Livestock Disease Diagnostic Center in Lexington. The syndrome, which has plagued central Kentucky breeding farms since late April, also appears to be cause of early fetal loss in at least 678 mares who have aborted their fetuses before 90 days of pregnancy. That figure, released by the Gluck Equine Research Center on May 10, is thought to have grown as more mares have reached their 60th day of pregnancy.

The center reported that on Monday, they had received 12 aborted or stillborn foals or fetuses for evaluation. The as-yet-undiagnosed syndrome has affected all equine breeds, but the center estimates that about 70 percent of the dead foals were Thoroughbreds.

Though researchers still have not officially diagnosed the syndrome, many believe it may be a mycotoxin, a fungus- or mold-produced toxin that can occur in pasture grass that horses eat.

Dr. David Powell, a Gluck Center epidemiologist, has said the center has some evidence that a similar syndrome might be occurring in states north of Kentucky, though he has declined to identify those states. Anecdotal reports have indicated that breeders in Ohio, Tennessee, and Illinois also are seeing higher-than-average abortion rates in mares.