Monensin and Lasalocid Toxicity in Horses

Important Concepts

• Ionophore Antibiotics: Monensin and lasalocid are used in poultry and ruminant feeds but are highly toxic to horses.

Clinical Signs

• Monensin:

  
  

  • Dose-dependent toxicity.

  • Depression, incoordination, weakness, paresis, paralysis, poor performance, heart failure, unthriftiness.

  • Cardiac arrhythmias, high heart rates, prominent jugular vein distension.

  • Acute ingestion can cause death within hours; chronic exposure results in prolonged symptoms like colic, diarrhea, stiffness, and muscle weakness.

  
  

Pathological Changes

• Cardiac Damage: Permanent damage to the heart muscles leading to heart failure and arrhythmias.

Diagnosis

• Definitive Diagnosis: Requires feed analysis or post-mortem examination.

• Clinical Evaluation: Symptoms suggestive of toxicity, changes in blood work reflecting dehydration and electrolyte imbalances.

Treatment

• Supportive Care: IV fluids, oral laxatives, anti-inflammatory, and pain medication.

• No Specific Antidote: Immediate removal of suspect feed sources is crucial.

Prevention

• Education: Ensuring feed companies prevent cross-contamination of equine feed with ionophore antibiotics.