Bureau of Land Management spokeswoman Lauren Gapinski says preliminary lab results indicate the ingestion of whorled milkweed, a highly toxic plant, is suspected to have caused the deaths. The weed was in the hay fed to the horses.
The Pueblo Chieftain reports the BLM began investigating after 11 horses died Dec. 3 and another eight died the following day. Some of the horses died on their own while others had to be euthanized.
Nine horses that showed illness have recovered or are recovering quickly.
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