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Articles of Interest donated by Christine Chambers

Following is from the University of Kentucky's College of Agriculture as of Friday, May 25, at 5 p.m.

We are able to report significant recent progress in accounting for Mare Reproductive Loss Syndrome (MRLS). Observations to date implicate cyanide or cyanogenic compounds as the causal agent. Wild black cherry trees are the likely source of these toxins. Limited recent imply the Eastern Tent Caterpillars may be directly or indirectly involved in the delivery of cyanogenic compounds to horses.

We want to emphasize that the current observations are preliminary, must be confirmed, and that further validation is absolutely essential. We have not yet met reasonable standards of scientific proof. Information summary briefs from several of the presentations made at the Mare Reproductive Loss Syndrome Information Sharing Meeting held yesterday at the Keeneland Sales Pavilion are posted to our web-site. In addition, several audio files of sound clips from the speakers are also posted. A replay of the entire meeting is also provided by a link with

There are several suggested recommendations from UK Extension Specialists for Pastures and Forages, Dr. Jimmy Henning and Dr. Garry Lacefield for horse producers as follows:

1. It should be considered safe to turn horses back out to pasture.

2. Mow pastures to dislodge any larvae or caterpillar
excrement from the leaves.

3. Do not confine horses in small areas that are surrounded by wild cherry trees.

4. Using temporary fencing to skirt off fence line areas next to high numbers of wild cherry trees may provide an extra level of safety.

Hay recommendations:

1. Fusarium mycotoxins were not found in any first cutting hay made before May 6th. It is therefore highly unlikely that properly cured hay from first or subsequent cuttings in Kentucky will cause any mycotoxin-related problems in horses.

2. Because of the possible presence of Eastern Tent Caterpillars in first cutting hay, producers should cull any hay from fields that had significant numbers of wild cherry trees in the proximity. This decision have to be made by the producer on a field by field basis.

3. Hay fields that are surrounded by cherry trees should be scouted for the presence of larvae or cocoons prior to cutting.

4. Future cuttings from these fields are considered safe because there would be no larvae or cocoons present.


Researchers Probing How Mares Ingested Cyanide; 150 Farms Surveyed

Scientists now believe they know why more than 500 foals died and mares spontaneously aborted several thousand more early pregnancies on central Kentucky's horse farms this spring.

Their work, however, is far from finished as they work to explain their theory conclusively and make sure they can help prevent a future outbreak of Mare Reproductive Loss Syndrome.

"We've come a long way in a fairly short period of time, but there's still a lot of things we don't understand," Dr. Thomas Tobin, a toxicology and pharmacology researcher at the University of Kentucky's Gluck Equine Research Center, said Wednesday. "We're confident we've zeroed in on cyanide and cyanogenic compounds as the problem. Now we have to determine how the mares ingested the poison."

Researchers and veterinarians began surveying more than 150 farms on Wednesday in an attempt to determine the exact conditions present on the farms during the last few weeks of April. The statistical data collected then will be analyzed by local scientists as well as those at the United States Department of Agriculture.

The on-site visits also will focus on the proximity of cherry trees to pastures in which pregnant mares may have grazed.

The prevailing theory suggests mares somehow ingested cyanide produced from the leaves of the trees, which are found on many of the region's horse farms.

"The extreme environmental conditions we had this spring, including several days of hard frost, may have damaged the leaves and made them even more toxic," Tobin said.

Low levels of cyanide, which inhibits the body's ability to receive and use oxygen, were found in the tissue of several fetuses. The poison may have caused foals to struggle for oxygen inside the womb.

"It wouldn't take a large amount of poison to affect an early-term embryo or a near-term foal," Tobin said. "We know that wilted leaves or broken branches from a black cherry tree are lethal to cattle and sheep."

Scientists also believe that Eastern tent caterpillars, which nest in the cherry trees and are immune to the poisonous chemicals in their leaves, may have played a role.

Tent caterpillars, which in Kentucky have now cocooned and are growing into moths, will be shipped from New York for study. Researchers will feed cherry tree leaves to caterpillars and monitor how the insects digest the toxins and how the toxins might be secreted and ingested by horses, Tobin said.

"We expect to have significant data from those tests back in about six to eight weeks," he said. "We hope they will be able to tell us exactly what, if any, part the caterpillars played in this scenario."

Scientists originally thought toxins generated by fungal- or mold-based agents in pasture grasses might have been behind the outbreak. But tests on hundreds of grass samples have been mostly negative for such toxins, Tobin said.

More than 100 scientists and staff from UK's College of Agriculture along with veterinarians, farm managers, leaders in the equine industry and other governmental and private agencies have worked around the clock for nearly a month to find the cause of the outbreak.

"The cooperative scientific and technical progress, made under the most urgent conditions in essentially a three-week period, is unprecedented anywhere," said Scott Smith, dean of the University of Kentucky College of Agriculture. "This effort has been a model of communication and cooperation, and will continue to be."

Current estimates show that up to 5 percent of this year's foal crop and as much as 29 percent of the 2002 crop may have been lost to the syndrome. Kentucky produces about 10,000 thoroughbred foals each year.

David Switzer, executive director of the Kentucky Thoroughbred Association, estimated the economic impact on the state's billion-dollar thoroughbred industry at between $200 and $225 million.

Those numbers are based on estimates of approximately 500 dead foals this year and 2,000 spontaneous abortions of horses that would have been born next spring.

The foals lost this year would have generated about $37 million in stud fees and sales revenue, and those lost that would have been born next year about $150 million, Switzer said.

Another $35 million to $38 million of the total number is lost income for companies that do business with horse farms.

"I think those numbers are on the conservative side," Switzer said. "If you don't have as many foals, you don't buy as much feed or hire as many stable workers. It's going to trickle down and hit everyone connected with the horse industry. Nobody is going to be untouched."