Ionophores such as monensin are feed additives used in cattle, poultry and other livestock. Horses are far more sensitive to them than cattle, so a feed-mixing error or access to cattle feed can cause severe heart and muscle damage, often in several horses at once. There is no antidote, which is why prevention is the central message.
Key facts
Ionophore toxicity at a glance- Species and system: horse; cardiovascular and skeletal muscle.
- Cause: ingestion of an ionophore such as monensin that was approved for cattle, chickens, goats or turkeys, not for horses (MSD).
- Sensitivity: monensin LD50 in horses is 2-3 mg/kg, versus 20-80 mg/kg in cattle and 20 mg/kg in dogs (MSD).
- Typical source: feed mill mixing errors, accidental overdose, misuse in a non-target species, accidental ingestion (MSD).
- Acute signs: weakness, anorexia, colic, profuse sweating, tachyarrhythmias, recumbency, sudden death (MSD).
- Treatment: no specific treatment or antidote (MSD); supportive care.
- Zoonotic: no.
What's inside
13 sections in the full guide- Key facts
- How the NAVLE tests this
- Cause and pathophysiology
- Clinical signs
- Diagnosis
- Differential diagnoses
- Treatment and management
- Prevention, control and public health
- Prognosis
- Putting it together in practice
- Quick review
- Test yourself
- References
The full guide also has 4 tables, 3 self-test questions and 7 references, available to NAVLE members.
Read the full study guide
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