Monensin poisoning

Attention! This is a potentially life-threatening condition for your horse. Time is of the essence, contact your veterinarian immediately.Find a Vet

Monensin Poisoning

Rumensin Poisoning, Coban 60 Poisoning, Ionophore Intoxication

Monensin is a monovalent carboxylic acid, used in the form of the sodium salt (monensin sodium), where it is typically purchased in the form of feed additive pellets. Monensin is one of several classes of antibiotics exclusively for veterinary use, known as ionophores. They are used as anticoccidial feed additives for poultry and cows, as growth promoters, and for improved feed efficiency in ruminants.

Cattle and poultry can ingest relatively high levels of monensin (Chickens - 200 mg/kg and Cattle 50-80 mg/kg) in their feed without any negative impact on their health. Horses and donkeys, however are highly sensitive to monensin. The LD50 value for oral ingestion of monensin in a donkey or horse is 2 mg/kg. For a 1100-lb (500kg) horse, this would require only 0.035 ounces of product containing monensin.

Unfortunately, incidents of poisoning in horse feeds occurs somewhat frequently. Toxic effects of ionophores are directed mainly against skeletal and/or cardiac muscle as a result of disturbances in muscle cell calcium homeostasis followed by increased intracellular Na+ concentration. The possibility of delayed effects on the heart is of major concern in horses exposed to monensin. Horse feed contaminated with monensin can sometimes be detected through smell of the feed. It is usually associated with a strong, 'bitter' odor.

Incubation Period
The incubation period varies depending on the amount of the toxin the horse ingests. Horses can start to develop signs from several hours to 4 months from first consuming the contaminated feed. Most horses that consume toxic levels of monensin, die within 48 hours of onset of signs.


Muscle wasting
Elevated heart rate
Dark red or brown urine
Intermittent sweating
Respiratory distress
Multiple horses affected
Weak, irregular pulse
Cyanotic mucous membranes
Jugular pulse
Sudden death


  • History
  • Clinical signs
  • Feed testing
  • Electrocardiogram (ECG)



Supportive care, there is no antidote.


  • Do not feed horses cattle or poultry feed and don't let them drink out of any water which is also shared by cattle or poultry, as sometimes drinking water is also treated with monensin.
  • Keep cattle and poultry feed locked up and not accessible by your horse.
  • Stay alert on current feed recalls on horse feeds from producers which also manufacture feed for poultry, cattle, and pigs.



Scientific Research

General Overviews