Thehorse.com - Full Article
by: Pat Raia
October 01 2011, Article # 19321
Minimize your horse's risk of ingesting a deadly plant by identifying and removing harmful species from in and around barns and pastures
One spring a few years ago, four horses on a Colorado farm began losing weight and developed photosensitization (a condition characterized by sensitivity to sun exposure) and neurologic signs. A thorough physical exam and blood work helped veterinarians determine the horses had extensive chronic liver disease, and a liver biopsy confirmed typical signs of pyrrolizidine alkaloid poisoning. These alkaloids are typically found in groundsels such as tansy ragwort, fiddle neck, and rattle pod. However, none of these plants were present in the horses' pasture.
But when the horses' owner broke open a bale from the hay supply he had been feeding all winter, he noticed significant amounts of broad, hairy leaves that were eight to 12 inches long. These leaves were identified as hound's tongue, a noxious weed in many areas across the country that contains significant quantities of pyrrolizidine alkaloids. Hound's tongue remains toxic even when dried in hay. These alkaloids have a cumulative effect on the liver, and after eating the contaminated hay over the winter, the horses developed chronic irreversible liver disease. Eventually, all four of the affected horses were euthanized because of liver failure.
Hound's tongue is one of myriad plants toxic enough to cause illness and even death in horses. So it's important that owners recognize poisonous plants growing in or near their horses' pastures and prevent their animals from ingesting them...
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