Diagnosis of Taxus (yew) poisoning in a horse.

The research presents an autopsy report of a horse that died suddenly and post-mortem investigations revealed it succumbed to Taxus (yew) poisoning. Previously, diagnosis of such poisoning was based on exposure history and presence of plant material in the gastrointestinal tract; but in this case, cardiac lesions were the first evidence of Taxus toxicity in horses.

Investigation Process and Findings

• The horse under investigation was a seemingly healthy 2-year-old Thoroughbred colt, which was found dead overnight in its stall without any previous known illnesses, diseases or toxic exposure. The report doesn’t give any information on visible clinical signs before the horse’s death.
• A necropsy was performed the next morning after the sudden death, revealing mild to moderate hemorrhages in both ventricles of the animal’s heart.
• Microscopic examination of the heart indicated acute mild multifocal necrosis within the papillary muscles and ventricles.
• The most incriminating evidence was the discovery of approximately 2% Taxus alkaloids in the stomach content of the horse. The presence of these toxic chemicals was confirmed through gas chromatography and mass spectrometry tests.

Significance and Implications

• This case is unique and important because, until this time, pathologies associated with Taxus poisoning were not documented in horses.
• This is the first report of cardiac lesions found in a horse after lethal exposure to Taxus.
• The discovery implies that exposure to Taxus should be considered in the differential diagnosis of horses that die suddenly or those having cardiac lesions suggestive of this type of toxicity, even if fragments of the plant cannot be physically identified in the stomach.
• The report has essentially broadened the understanding of Taxus toxicity in horses and opens up new grounds for veterinary investigations when dealing with sudden unexplained equine deaths.