Summer pheasant’s eye (Adonis aestivalis) poisoning in three horses.

This article reports a case where three horses died after consuming hay infested with a plant called summer pheasant’s eye (Adonis aestivalis), which produced toxins similar to those found in oleander and foxglove plants. Their symptoms started with colic and later developed into severe cardiac conditions which led to their deaths.

Introduction and Background

• The study reports a case of three horses that ingested stems and leaves of the plant Adonis aestivalis, commonly known as summer pheasant’s eye, which was found in the hay they were fed.
• This was the first case of Adonis aestivalis poisoning reported in North America, and it brings attention to its toxicity which hadn’t been described previously in connection with livestock.
• Adonis aestivalis contains a type of toxin called cardenolides, which are also present in the plants oleander and foxglove. These toxins primarily affect the heart and, to a lesser extent, the digestive system.

Clinical Findings

• All three horses showed initial signs of colic 24-48 hours after exposure to the hay. Gaseous distension in the gastrointestinal tract was the main observed symptom.
• Two of the horses then became extremely weak just a day after showing the first signs of discomfort and were euthanized. The third horse was euthanized after 4 days of medical treatment.
• Necropsy (the autopsy of an animal) of the first two horses showed endocardal hemorrhage (bleeding inside the heart) and gaseous distension of the gastrointestinal tract.
• Microscopic examination of these horses revealed mild acute myocardial necrosis and inflammation associated with bleeding in the endocardium and epicardium (innermost and outermost layers of the heart).
• The third horse, which survived longer, showed signs of acute, subacute, and chronic myocardial necrosis and degeneration – representing damage to the heart muscle over a more extended period.

Identification of the Toxin and Conclusion

• The toxic plant, Adonis aestivalis, was identified in the hay provided to the horses.
• Strophanthidin, the active component of several cardenolides (heart-affecting toxins) present in Adonis species, was detected in the gastrointestinal contents of all three horses. This was done using liquid chromatography-mass spectrometry, a highly sensitive technique for identifying chemical compounds.
• The authors conclude that although it is known that Adonis species contain cardiac glycoside toxins, the cardiac lesions observed in this case had not been previously associated with the consumption of Adonis by livestock.
• This case strongly suggests that ingestion of Adonis aestivalis can cause severe and deadly gastrointestinal and cardiac conditions in horses.