Q: Is there any danger in horses grazing frosted pastures in the fall? If so, how long would you wait?
A: Some deciduous leaves can be deadly after a frost or after they have wilted due to broken branches, fall leaf shed or storm damage. Leaves of greatest concern for horses are wilted maple and prunus species, including chokecherry, ornamental almond, and cherry trees. Horse owners should identify all such seasonally toxic trees on the property, and keep horses from their fallen or frost damaged leaves for at least 30 days. Even though these leaves are not commonly eaten, horses can accidentally ingest them, especially if hungry or bored.
Cyanide toxicity can also be an issue after frost. There are no reports of toxicity of horses grazing frost damaged grass, alfalfa, or clover. However, frost damaged pasture forages can have higher concentrations of sugars, leading to an increase in potential for founder and colic. To reduce the chance of adverse health effects, it is recommend that horse owners wait up to a week before turning horses back onto a pasture after a killing frost.
By Krishona Martinson, PhD, University of Minnesota