Horse lovers, veterinarians and scientists alike have long wondered why horses put out to pasture in the fall are so prone to contracting a deadly muscle disease that can kill the animals within days. Now, a team of University of Minnesota researchers may have found the answer.
A toxin found in the seeds of box elder trees was recently found to be behind the equine muscle disease seasonal pasture myopathy. Otherwise known as SPM, the disease is fatal in over 90 percent of cases.
Stephanie Valberg, Ph.D., D.V.M., director of the University of Minnesota Equine Center, led a team of U of M collaborators including plant pathologist, animal science, veterinary, biochemist and horticulture experts to make the discovery.
“We’ve wondered for hundreds of years why horses put out to pasture in the fall die from severe muscle damage,” said Valberg. “When we examined the white snakeroot, which was previously believed to cause seasonal pasture myopathy, we found it wasn’t always present where horses were becoming sick, so clearly it wasn’t the answer.”
This finding led Valberg to consult with U of M College of Food, Agriculture, and Natural Resource Sciences on another suspected culprit found at every horse pasture involved in the study: the seeds of the box elder tree.
An analysis by the U of M Department of Horticulture Science revealed box elder tree seeds contained the toxin hypoglycin A and blood samples confirmed the toxin was consumed by affected horses. Box elder seeds appeared to be responsible for seasonal pasture myopathy.
This discovery led to an understanding that when a sufficient quantity of the box elder seeds and their toxins were consumed, a breakdown of respiratory, cardiac, and posture-related muscles occurred.
A European-equivalent of seasonal pasture myopathy known as atypical myopathy is suspected to have a similar cause.
Valberg’s team and their collaborators are currently working to help horse owners and veterinarians identify and prevent this deadly disease in both Europe and the U.S.
More information on their ongoing work and findings can be found here.