Bryony Plant Poisoning in Horses

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Bryonia dioica Toxicity in Horses

Bryonia dioica, or bryony, is an invasive plant that is known to climb buildings, trellises, fences, barns, stables, homes, trees, and even over other hedges. It is most often found in hedgerows and open wooded areas, and grows most vivaciously in areas with a temperate climate. In the U.S., the bryony plant is more commonly found in the Northwest states.

Both white bryony and black bryony are known for being highly toxic to the intestinal tract. While the whole plant is toxic to a horse (i.e., leaves, berries, vines), the berries and roots of the plant hold the most poison. The coloring of the berries is best way to distinguish between the two types of bryonies. While both plants’ berries begin green, the white bryony's berries ripen to black colored berries, while the black byrony's berries ripen to red colored berries. The plant is described as having an unpleasant odor, so horses will generally not eat from the plant as a first option, but may do so if left without other suitable forms of feed.

Knowing what the bryony's leaves and berries look like, and ensuring that your horse does not have access to it, is critical to protecting your horse from the plant's toxic effects. 


The main side-effect of bryony toxicity is as an intense laxative. Some of the symptoms that may be seen are:

  • Soft stool, diarrhea
  • Excessive urination (polyuria)
  • Elevated temperature
  • Profuse sweating
  • Trouble breathing (dyspnea)
  • Muscle tremors
  • Muscle spasms


  • Ingestion of the bryony plant  - especially the berries and roots
  • Ingestion of any part of the plant may have a toxic effect in the intestinal or respiratory system


It often proves difficult to determine the exact cause of poisoning in a horse. A veterinarian should always be consulted when some type of poisoning is suspected, and especially so if you have determined that you have a poisonous plant growing on or near your property, and your horse is exhibiting symptoms of illness. Your veterinarian will perform a thorough examination, which may also include blood and urine analysis. These tests will not tell the veterinarian exactly what toxin has been ingested, but will give clues to the damage that is occurring in the horse so that proper medical action may be taken.

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