Crofton weed (Eupatorium adenophorum) toxicity in horses.

This study examines the symptoms and pathology associated with a respiratory disease in horses, found in south-eastern Queensland, believed to be linked to ingestion of the Crofton weed (Eupatorium adenophorum), summarizing 6 case studies and various experimental feeding trials.

Overview of the Study

• The research describes a specific respiratory disease that affects horses in the south-eastern Queensland region.
• This illness has been reported over a significant period of time and is commonly suspected to be linked with the consumption of a particular plant known as Crofton weed, scientific name Eupatorium adenophorum.

Symptoms and Pathology

• Observed symptoms in the affected horses involve coughing, rapid, intense breathing, decreased physical activity tolerance and overall loss of body condition.
• For horses with longstanding exposure to the plant, particular pathological signs were identified including: fibrosis (excessive formation of connective tissue), proliferating alveolar lining cells (increased production of lung air sacs cells), oedema (fluid accumulation in body tissues), neutrophil infiltration (white blood cells moving into the tissue), and abscessation (formation of abscesses).
• Some instances also showed the occurrence of vascular thrombosis (formation of blood clots in the vessels) and infarction (tissue death due to insufficient blood supply) in the lungs.

Feeding Experiments

• The symptoms and lesions observed in the case studies were replicated in a horse who was deliberately fed E. adenophorum over a span of 8 months. Early stages of the disease were identified in another horse that was fed the flowers of the plant for around 6 weeks.
• Further, experiments were conducted on other species as well. Rabbits that were fed the plant also developed similar lesions. However, when sheep and rats were subjected to the same experimental diet, these symptoms failed to manifest, indicating potential species-specific toxicity of the plant.