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United States Department of Agriculture

Agricultural Research Service

Title: Knowledge is key to safety; Plants that poison horses

Author
item Stegelmeier, Bryan

Submitted to: DVM The Newsmagazine of Veterinary Medicine
Publication Type: Other
Publication Acceptance Date: July 1, 2007
Publication Date: August 1, 2007
Citation: Stegelmeier, B.L. 2007. Series of articles. Article I: Knowledge is key to safety; Plants that poison horses. August 1, 2007; Article II: Plants poisonous to horses: the neurotoxic variety. pp.1-5, September 1, 2007; Article III: Identifying poisoning signs, sequelae. October 1, 2007; Article IV: Identifying nephrotoxic plants, and how to minimize poisoning. November 1, 2007.

Interpretive Summary: Horses are relatively selective grazers and generally they are poisoned less frequently than other livestock. However, there are exceptions. Some poisonous plants are palatable to horses and exposed horses readily eat them. Others may be eaten by some animals even though they are unpalatable to the rest of the herd. As individual horses may actively seek and eat toxic plants, it has been suggested they become addicted to certain toxic plants. There is little experimental support for addiction, but individual horses do develop strong feed preferences. Such animals certainly pose greater risk to poisoning. As a rule, both preferences and palatability are different when poisonous plants are dried and included in stored feed. Most horses readily accept toxic plants that are included in hay or processed feed. In herd situations, competition for food can enhance poisoning as animals hurry to eat what they can or fight to keep lesser status animals from eating. As antidotes are rare; plant toxin-induced diseases can be irreversible; and some poisonings are lethal: knowing the risks and sequelae of poisoning is essential. The purpose of this first of a short series of papers is to briefly introduce the hepatotoxic plants that poison horses in North America, describe poisoning and the subsequent plant induced disease, and outline current recommendations for treatment as well as management practices to avoid exposure to the plants.

Technical Abstract: Horses are relatively selective grazers and generally they are poisoned less frequently than other livestock. However, there are exceptions. Some poisonous plants are palatable to horses and exposed horses readily eat them. Other plants may be eaten by some horses even though they are unpalatable to the rest of the herd. As individual horses may actively seek and eat toxic plants, it has been suggested they become addicted to certain toxic plants. There is little experimental support for addiction, but individual horses do develop strong feed preferences. These horses certainly pose greater risk to poisoning. As a rule, both preference and palatability are different when poisonous plants are dried and included in stored feed. Most horses readily accept toxic plants that are included in hay or processed feed. In herd situations competition for food can enhance poisoning as animals hurry to eat what they can or fight to keep lesser status animals from eating. As antidotes are rare, plant toxin-induced diseases can be irreversible and some poisonings lethal. Knowing the risks and sequelae of poisoning is essential. The purpose of this series of papers is to introduce hepatotoxic plants that poison horses in North American, describe poisoning and the subsequent plant-induced disease and outline current recommendations for treatment as well as management practices to avoid exposure to the plants.

Last Modified: 7/28/2014
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