Crofton weed (Eupatorium adenophorum) toxicity in horses

Area of Science:

• Veterinary Pathology
• Equine Medicine
• Toxicology

Background:

• A chronic respiratory condition affecting horses in coastal Queensland has been observed for years.
• This disease is suspected to be linked to the ingestion of Crofton weed (Eupatorium adenophorum).

Purpose of the Study:

• To describe the clinical signs and pathological findings of this equine respiratory disease.
• To investigate the role of Crofton weed (Eupatorium adenophorum) in the development of the disease.

Main Methods:

• Clinical and pathological examination of six field cases of the respiratory disease in horses.
• Experimental feeding of Crofton weed (Eupatorium adenophorum) to horses, rabbits, sheep, and rats.

Main Results:

• Clinical signs in affected horses included coughing, rapid respiration, reduced exercise tolerance, and weight loss.
• Pathological findings revealed lung fibrosis, alveolar lining cell proliferation, edema, neutrophil infiltration, abscessation, and in some cases, vascular thrombosis and infarction.
• Horses experimentally fed E. adenophorum developed similar signs and lesions; rabbits also developed lesions, while sheep and rats did not.

Conclusions:

• Crofton weed (Eupatorium adenophorum) is implicated as the causative agent of this respiratory disease in horses.
• The study provides pathological evidence supporting the link between E. adenophorum ingestion and equine respiratory disease.