Delayed monensin sodium toxicity in horses

Area of Science:

• Veterinary Medicine
• Toxicology
• Equine Health

Background:

• Monensin sodium is an ionophore widely used in cattle feed.
• Equine ingestion of monensin-containing feed is accidental and can lead to toxicity.
• Poor performance and unthriftiness are common presenting complaints in horses with potential monensin toxicity.

Purpose of the Study:

• To investigate the cardiac effects of monensin sodium ingestion in horses.
• To identify clinical and pathological findings associated with monensin toxicity in equine cases.
• To establish the link between monensin exposure and cardiac myodegeneration.

Main Methods:

• Clinical examination of 32 horses with a history of poor performance post-monensin exposure.
• Diagnostic workup including cardiac abnormality assessment.
• Necropsy examination of 6 severely affected horses.

Main Results:

• Cardiac abnormalities were diagnosed in 8 horses and suspected in 4 others.
• Necropsy revealed marked cardiac myopathy and fibrosis in cases with circulatory failure.
• Clinical signs correlated with pathological findings of specific cardiac myodegeneration.

Conclusions:

• Monensin sodium ingestion in horses can cause significant cardiac damage.
• This toxicity can manifest as acute death or delayed cardiac circulatory failure.
• Specific cardiac myodegeneration is the underlying pathology of monensin-induced heart disease in horses.