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Mare Reproductive Loss Syndrome (MRLS) Confirmed in Florida




The University of Florida’s College of Veterinary Medicine has confirmed two cases of MRLS and has one other case that is suspect. All three cases occurred in Alachua County this spring. At this time, it is strongly recommended to mare owners that all abortions and foal deaths receive a post-mortem evaluation.


Inspection of pastures for the presence of cherry trees and Eastern Tent caterpillars also is critical. According to Dr. Dana Zimmel of the university of Florida’s College of Veterinary Medicine, one mare produced a septic foal on March 18, 2006 that was euthanatized after two days of intensive treatment. Samples from an earlier abortion on the same farm were re-examined and showed indications of MRLS.

The third case was a foal born on march26, 2006 that was treated in the neonatal intensive care unit at the University of Florida for 12 hours before being euthanatized. In the Kentucky outbreaks of 2001-2002, there was a strong association between the presence of unusually large numbers of eastern tent caterpillars (ETC) and MRLS. Eastern tent caterpillars were found on the Alachua County farms and have been collected for future study. Research has been ongoing since the Kentucky outbreak began in 2001.

The most recent information on the state of this research was published by The Horse in December 2005. In that article, Bruce Webb, a University of Kentucky entomologist who has been studying MRLS, said, “We can prevent mare reproductive loss syndrome as we experienced in 2001 and 2002 by keeping horses away from caterpillars.”


Mare reproductive loss syndrome, which historically can cause late-term abortions, early-term fetal losses, pericarditis (heart problems), unilateral endophthalmitis (problem in only one eye), hyphema (blood in the eye) in foals, mouth ulcers and laminitis was first seen in Kentucky and surrounding states (and as far north as Canada) in 2001, with a reduced incidence in 2002.


In 2001, there were 516 late-term abortions and 2,998 early fetal losses in Kentucky’s Thoroughbred industry alone. There also were about 60 cases of pericarditis and 50 cases of unilateral uveitis reported in Central Kentucky horses.

More than 30 percent of the anticipated 2002 Thoroughbred foal crop in Kentucky was lost due to MRLS. The economic cost to the state from losses suffered by all horse breeds was estimated at nearly USD 336 million, according to a study commissioned by then-Kentucky Governor Paul Patton and conducted by the University of Louisville's Department of Equine Business.

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