Mare Reproductive Loss Syndrome - Tent Caterpillars

Spring is here and as the new foals begin to arrive, they are not the only new young creatures showing up on the scene. Also beginning to hatch are the larvae of the Eastern Tent Caterpillars and Forest Tent Caterpillars. What does this have to do with your horse or my Arabian horses?

You may remember in 2001 there were a large number of thoroughbred foals dying in Kentucky and no one knew why. The problem was threatening the racehorse industry and it was imperative to the economy of the state that the reason behind the deaths be identified.

I remember hearing the stories about the dying foals and updates as the numbers of foals increased but don't recall ever hearing what was being done to solve the mystery

I also didn't hear that it wasn't just the thoroughbred farms but 17 other breeds of horses affected. At least one report states was not just limited to the one area of Kentucky. It spread over a number of states. By the time the epidemic ran it's course 4,000 mares had aborted with economic losses reaching $500 million.

The outbreak was catastrophic. The new stories covered the globe as concerns spread about threats to the world horse industry. The state department and FBI were involved wondering about the possibility of contagion associated with agri-terrorism

Mare Reproductive Loss Syndrome was the name given to the phenomenon that included death to fetuses in all stages of development and even foals born alive but dying. What does this have to do with Eastern Tent Caterpillars. Unveiling a Six-Legged Equine Assassin: Mare Reproductive Loss Syndrome describes how the caterpillar became suspect.

Studies were done that proved the caterpillars were the problem but still no one knew specifically why the caterpillars were killing the horse fetuses and foals.

"A series of studies over the next five years has subsequently revealed that horses will inadvertently eat the caterpillars and that the caterpillar hairs embed into the lining of the alimentary tract. Once that protective barrier is breached, normal alimentary tract bacteria may gain access to and reproduce in sites with reduced immunity, such as the fetus and placenta. Fetal death from these alimentary tract bacteria is the hallmark of MRLS. " Quote from MRLS: Eastern and Forest Tent Caterpillars Currently Feeding

The time is right for spraying for caterpillar larvae and keeping these pests out of horse pastures where they might be ingested. While the epidemic was restricted to the Kentucky area where the wild cherry trees this particular species of caterpillars thrives, it would seem to me that making sure that any kind of caterpillar larvae in any part of the country might be wise.

The Kentucky outbreak was what it was because of the large numbers of horses it affected and the economic impact to the horse industry. That's what spawned all the research. The numbers of the larvae were also larger than the norm which contributed to the disaster.

To date, no one's really looking at the effect across the board to horses in general that might ingest caterpillar larvae of any kind. It seems to me that MRLS could easily be the explanation for odd abortions across the country. While it may be a while before science catches up, I think spraying for caterpillars this time of year is a simple enough precautionary step to use to protect my Arabian horses just in case MRLS isn't just restricted to these two forms of caterpillars.
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