Detoxifying Cyanide

According to Dr. Terry Fitzgerald, the Eastern tent caterpillar does a very good job of detoxifying the cyanide it ingests when eating the leaves of black cherry trees. Fitzgerald, a distinguished university professor of biological sciences at the State University of New York College at Cortland, is an expert on tent caterpillars and their habitats. Researchers at the Gluck Equine Research Center at the University of Kentucky have been working with Fitzgerald because of his knowledge in this area. The professor has studied the Eastern tent caterpillar since 1976.

Fitzgerald explained that these caterpillars detoxify cyanide when it passes through their digestive tracts. “By the time it is a fecal pellet, there isn’t much cyanide left, only a fraction of what was in the leaves,” explained Fitzgerald.

“The image projected that cyanide was raining down out of trees in caterpillar fecal material is not true,” asserted Fitzgerald. “There is some cyanide there (in the feces), but is it enough to cause problems in horses?”

There is up to 4,000 parts per million (ppm) of cyanide in young leaves of black cherry trees that caterpillars prefer to eat, said Fitzgerald. There is 50-100 times less cyanide by weight basis in the fecal pellets than in the leaves.

“It (the caterpillar feces) does contain a little bit of cyanide, but the caterpillar is good at breaking down the cyanide quickly,” he said. “The cyanide disappears in the caterpillar’s body quickly.

“The question is, is there enough cyanide in the fecal pellets to do damage to the horse, and will they (horses) eat the material?”

The professor also pointed out that because the caterpillar is so proficient at detoxifying the cyanide it ingests, that by the time the caterpillar leaves the tree and makes it into a field, there is a low quantity of food in its gut, and that food is already partially detoxified.

Fitzgerald is gearing up to do a larger study of the Eastern tent caterpillar next year, collecting caterpillars at various stages of growth and feeding. “We got a late start this year because caterpillar season was nearly over by the time I got involved,” he explained.

“This was an excellent year for caterpillars," said Fitzgerald earlier this year. "Next year should be a very big year, too, where I am located (New York). Then another year there should be a lot, then the numbers will crash because of a bacteria or virus or weather."

He said the Eastern tent caterpillar develops over time into a very large population, then the population "crashes." It takes four or five years for them to appear again, then about every 10 years the population cycles back to an "outbreak" in the number of caterpillars.

Fitzgerald theorized this spring that 2001 might just have been a bumper year for young black cherry trees. He suggested that horses grazed the trees under fences or electric wires where bird droppings included seeds. Fitzgerald said that by this time of year in un-grazed and un-mowed areas, black cherry tree seedlings would be eight to 12 inches tall.

“The production of trees is not regular each year,” explained Fitzgerald earlier today. “You might see hundreds of seedlings one year, and very few the next several years. Cherry tree seeds can stay underground for several years. If the seedlings are a factor, then you would not expect to see this phenomenon (foal losses) every year.”

He said it has been suggested that there might be as much as 3,000-5,000 ppm cyanide in one leaf of a black cherry tree seedling, but it isn’t known for sure. Fitzgerald currently has seeds of black cherry and choke cherry trees, but they must be kept cold for at least three months before they can be germinated. Fitzgerald then will grow the trees and measure how much cyanide is found in the young leaves.

The cause of the various syndromes seen in the Eastern part of the United States and Canada, especially in the Ohio Valley, is still not known. Research is continuing to try and piece the puzzle together.

About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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