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Amy K. Stone, Ohio State University Extension, Lucas County; Joseph F. Boggs, James A. Chatfield, Mary Maloney, Erik A. Draper, Hannah Mathers, Pamela J. Bennett, Jane C. Martin, Marianne Riofrio, |
What Killed the Foals?
Dan Potter led a discussion regarding the on-going search for last season's widespread loss of Thoroughbred and other foals in Kentucky. The problem is now known as Mare Reproductive Loss Syndrome (MRLS) and was characterized by extremely high fetal mortality rates during the spring of 2001. The topic was particularly poignant and fitting given the location of the Bluegrass BYGLive! The economic impact of the foal deaths was estimated to exceed some $336 million through 2003, with more than $300 million of that centered in the Bluegrass region around Lexington. And the problem was not confined to Kentucky alone, but spread to neighboring states.
Early speculation focused on the possible role played by the extremely high populations of eastern tent caterpillar experienced this past spring in the Kentucky horse region. While the caterpillars feed on a wide range of hosts, cherry trees are preferred, and black cherry is very common in central Kentucky.
It was speculated that the caterpillars somehow served as a vehicle to carry the cyanogenic compounds contained in the cherry leaves to the horses. Observations that some symptoms appeared to be consistent with cyanide poisoning seemed to support this theory. Consequently, some horse farms have implemented a black cherry removal program. So far, Gainesway has not moved in this direction.
Dan noted that research conducted thus far by a colleague in the Department of Entomology indicates that it is highly unlikely the caterpillars delivered cyanide to the horses.
The caterpillars are apparently very good at detoxifying the cherry leaves, and virtually all the cyanide was removed in the caterpillars foregut. The compound was not found in the midgut, the hindgut, or the frass (excreta). It was also not incorporated into the body of the caterpillars. Although cyanide was present in the foregut, it was calculated that a horse would have to consume more than 2,000 lbs. of caterpillars in order to experience a toxic reaction.
The search for a causal agent is being pursued down several paths, but as with many puzzles encountered in nature, guideposts illuminated by solid scientific evidence remain elusive. Likewise, pitfalls have been impossible to avoid.
The entire story thus far provides a fascinating glimpse into the practical application of the scientific process. To the credit of UK, no final conclusions have been drawn, and the research continues.