Summer pheasant's eye (Adonis aestivalis
) is a small herbaceous perennial plant with large buttercup-like blossoms and soft, fern-like leaves. It is native to Europe and Asia, and was introduced to other areas of the world as a garden ornamental. A. aestivalis
was introduced into North America initially as a horticultural plant, however it escaped cultivation and now grows in the wild in the western United States (California, Oregon, Washington, Idaho, Montana, and Utah), Missouri, and New York. It grows abundantly in open forests and disturbed sites in the Western states. It also grows in hay fields, and on occasion can get mixed in with hay when baled.
All parts of A. aestivalis
contains cardiac glycosides, which are cardiotoxic to horses, resulting in fatal digestive and cardiac disturbances. Specific chemicals include adonitoxin, strophanthin, vernadigin, and cymarin. The leaves and flowers have the highest concentration of toxins.
In 2004, three horses died from eating grass hay containing A. aestivalis
. The hay appeared normal to the naked eye, but most of the 20 horses that were fed the hay refused to eat it. The three horses that died began to show clinical signs of gastrointestinal disturbances and myocardial necrosis after consuming the hay contaminated with A. aestivalis
24-48 hours after they were first exposed.
In a 1952 there were reports of four separate cases in which horses were fed alfalfa hay contaminated with A. aestivalis