Weed seeds toxic to horses

  • Weed seeds are most commonly a problem as a contaminant in grains.

  • As little as 0.25 percent of a horse’s bodyweight in corn cockle seeds can be toxic.

  • 0.3 to 0.7 percent of a horse’s bodyweight in eastern black nightshade berries can be toxic and may cause death.

  • Cleaning or blowing oats can help prevent toxicity.

In this article we will cover corn cockle seeds, mustard seeds and Eastern black nightshade berries.

Identifying

Weed seeds come in many shapes, colors and textures.

  • Corn cockle and mustard seeds are round or oval in shape and dark brown or blackish in color.

  • Eastern black nightshade berries are small and round. They turn from green to dark purple or black when ripe.

Corn cockle seeds
Corn cockle seeds
Mustard seeds
Mustard seeds
Eastern black nightshade berries
Eastern black nightshade berries
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Toxicity

Weed seed-contaminated oats
Weed seed-contaminated oats

The seeds relative to their plant, contain the highest level of toxic chemical. Seeds are usually a problem when they occur as a contaminant in grain (e.g. oats or soybeans).

  • As little as 0.25 percent of a horse’s bodyweight in corn cockle seed can be toxic.

  • 0.3 to 0.7 percent of a horse’s bodyweight in eastern black nightshade berries can be toxic and may cause death.

  • A toxic amount of mustard seed is unknown.

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Control

Weeds seeds are common in “bin run,” unblown or unscreened oats. Blowing or screening oats separates the smaller weed seeds and other foreign matter from the oats. Commercial grain sellers and feed stores commonly blow or clean oats. If you grow your own oats, make sure they are blown or cleaned before feeding or seeding.

Other information

Some weed seeds can live dormant in the soil for 20 years or more years. This causes weed problems in pastures and hay fields. Most seeds grow in the first few years after they fall from the plant. Regardless, weed control efforts should focus on reducing or eliminating weed seed production.

Photos provided by Krishona Martinson, PhD, University of Minnesota Extension and the University of Minnesota Strand Memorial Herbarium.

Krishona Martinson, equine Extension specialist; Lynn Hovda, DVM, adjunct assistant professor, College of Veterinary Medicine; Mike Murphy, DVM, former professor, College of Veterinary Medicine

Reviewed in 2018

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