Horses that have ingested ionophores show which necropsy finding?

Horses that have ingested ionophores show which necropsy finding?

• A. Skeletal muscle necrosis
• B. Myocardial chamber dilation
• C. Liver necrosis
• D. Myocardial necrosis

Answer: (D)

Ionophores are highly cardiotoxic in horses, so the hallmark lesion seen at necropsy is death of heart muscle. These compounds disrupt ion transport across cell membranes, leading to calcium overload and mitochondrial dysfunction that drive cardiac myocyte necrosis. The heart’s high energy demands make it especially susceptible, so myocardial necrosis stands out as the most consistent finding. Skeletal muscle necrosis can occur with ionophore exposure, but it’s less specific and not the primary lesion described. Liver necrosis is not typically a primary feature, and chamber dilation reflects a functional consequence rather than the initial tissue injury. Therefore, myocardial necrosis best matches ionophore ingestion in horses.

Ionophores are highly cardiotoxic in horses, so the hallmark lesion seen at necropsy is death of heart muscle. These compounds disrupt ion transport across cell membranes, leading to calcium overload and mitochondrial dysfunction that drive cardiac myocyte necrosis. The heart’s high energy demands make it especially susceptible, so myocardial necrosis stands out as the most consistent finding. Skeletal muscle necrosis can occur with ionophore exposure, but it’s less specific and not the primary lesion described. Liver necrosis is not typically a primary feature, and chamber dilation reflects a functional consequence rather than the initial tissue injury. Therefore, myocardial necrosis best matches ionophore ingestion in horses.