Which signs are typical of monensin toxicity in horses?

• A. Colic, sweating, tachycardia, weakness
• B. Coughing and sneezing
• C. Diarrhea only
• D. Lameness only

Answer: (A)

Monensin is a potent ionophore that horses are unusually sensitive to. When ingested, it disrupts ion transport in skeletal and cardiac muscle cells, leading to muscle injury and systemic distress. The result is a pattern of signs that reflects abdominal pain plus autonomic and muscular involvement: colic from intestinal and muscle soreness, sweating from pain and stress, a fast heart rate as the body responds to distress, and generalized weakness from muscle damage. The other options don’t match this multi-system toxicity: respiratory signs like coughing or sneezing aren’t typical of monensin poisoning; diarrhea alone doesn’t capture the broader signs of muscle and cardiac involvement; lameness alone doesn’t reflect the characteristic gastrointestinal and autonomic findings. So the combination of colic, sweating, tachycardia, and weakness best represents monensin toxicity in horses.