Photograph by Melissa Farlow
Mares wear muzzles to prevent them from eating disease-causing eastern tent caterpillars.
Scientists believe the mysterious illness that caused equine abortions in central Kentucky for the past two years will not strike the state's famed industry with such vengeance a third time. Mare Reproductive Loss Syndrome (MRLS) killed up to 20 percent of the foal crop in 2001, led to the cancellation of this year's major money-making yearling sale, and cost the billion-dollar-a-year industry millions.
Why the optimism? Scientists believe there is less chance the area will be invaded by the hairy insects area farmers have come to dread. "Where there have been high numbers of eastern tent caterpillars, there have been high numbers of abortions," says Lee Townsend, an entomologist at the University of Kentucky College of Agriculture. "Careful examination of many central Kentucky wild cherry trees over the past few weeks point to a very low population this year." Such insects have a natural cycle of strong populations for three or four years. Then their numbers drop because of crowding and disease, according to Townsend.
However, since most farmers begin breeding their horses in mid-February, it is still too early to be certain MRLS won't be a problem. Most of the abortions in 2001 and 2002 occurred 40 to100 days after conception. "In 2001 and 2002 the abortions occurred in the weeks preceding the Kentucky Derbyin April," says Nancy Cox, Associate Dean of Research at University of Kentucky's College of Agriculture.
So far, equine abortions in the area this year are down slightly in all horse breeds according to the University of Kentucky, which monitors premature foal deaths. A certain percentage of abortions do occur naturally in the breeding season.
Horse farms have also taken extra precautions to protect their prized equine mares from MRLS this season, another reason for the optimism. "Lots of horse producers in 2002 got ready for the season by cutting down cherry trees, muzzling their horses, restricting access to pastures, and other things. MRLS was very much reduced in 2002 and people have continued with those strategies in 2003," says Cox. This year farm managers are also advised to spray or inject cherry trees with insecticide to kill caterpillars. "Couple that planning with fewer caterpillar masses and it does portend for a better season for us," Cox said.
The eastern tent caterpillar is predominantly found throughout the eastern half of the United States and seems to prefer nesting in wild cherry trees, a common sight on Kentucky horse farms. When caterpillars emerge from their nests, they feed off the trees until they reach the pupa stage or the tree loses its leaves. When the caterpillars travel pastures searching for other food sources, mares can easily ingest them while grazing.
Although caterpillar populations are down and horse farmers have steeled their acres for the season, area scientists and veterinarians are still determined to find out exactly how this common insect could cause abortions in much larger mammals. Research will focus on discovering if the causal agent is natural to the caterpillar or if it is some kind of chemical compound not native to the animal. Says Cox, "We're confident after this year we'll be a lot farther down the road to finding out the exact cause."