Horses Poisoned by Milkweed

Nineteen horses that died at the Wild Horse Inmate Program facility in Colorado were probably poisoned by narrowleaf whorled milkweed that was in baled hay, according to findings from the Veterinary Diagnostic Laboratory at Colorado State University.

A number of other horses at the facility became ill after eating the hay, but later recovered. The facility is run by the Bureau of Land Management and houses about 2,000 horses and 400 donkeys.

Affected horses showed signs of neurologic impairment including incoordination, weakness, and seizures. Tests for infectious diseases were negative.

Ingestion of even small amounts of milkweed can cause serious illness or death. Horses usually avoid eating the plant when they are grazing, but may unknowingly consume dried milkweed that has been included in baled hay.