What is Monensin Toxicity?
It only takes a small amount of monensin concentration in the feed to be toxic, or even lethal. This additive has the chemical property ionophore, which slows the transportation of potassium and sodium across the cell membranes. Cattle can handle about 20 milligrams per kilogram of their total weight, but horses will get sick with only a fraction of that (2 milligrams per kilogram). Monensin is poison to any kind of horse so if you think your horse ingested any amount, it is important to call your veterinarian for an appointment.
Farm owners who wish their cattle and poultry to grow faster and larger have been using monensin in their feed for many years with no problem. However, problems ensued when horses started getting sick with monensin toxicity. After careful study, experts realized that just a trace of monensin in a horse’s feed can cause serious illness because equines are much more sensitive (20 times more sensitive) to ionophores. It was determined that horses were somehow eating the feed meant for cattle and poultry, and furthermore, that horse feed produced in those businesses were being tainted with monensin as well.
Monensin (ionophore) is an antibiotic and growth additive in bulk feeds for cattle and poultry, but can be deadly if consumed your horse. In fact, your horse may be poisoned even if their feed does not have monensin in it, but was made at a plant that also makes feed with the additive.
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Symptoms of Monensin Toxicity in Horses
The symptoms of monensin toxicity may be mild or severe, depending on the amount consumed and length of time it was eaten. However, some of the most often reported signs of monensin toxicity in horses include:
- Walking abnormally
- Excessive sweating
- Exercise intolerance
- Appetite loss
- Rapid breathing and heart rate
- Inability to get up
- Kidney failure (dark urine, fluid retention)
- Muscle wasting
- Heart failure
- Acute monensin toxicity occurs when your horse eats a large amount of monensin in a short period of time
- Chronic monensin toxicity is from eating small to moderate amounts of monensin for a long period of time (more than one month)
Causes of Monensin Toxicity in Horses
The cause of monensin toxicity in horses is the consumption of feed that contains ionophore. It does not have to be a large amount of feed, just traces of this substance is toxic to horses.
- Eating feed meant for cattle or other animals like poultry
- Buying feed that is made in a place that makes feed for cattle with monensin
- Accidentally feeding horses the feed meant for cattle
Diagnosis of Monensin Toxicity in Horses
The veterinarian will need to obtain your horse’s medical history, immunization records, work and living conditions, and be told of any symptoms you have seen. Describe the food that you believe your horse consumed and bring a sample or the package, if possible. Your horse’s vital signs will be recorded and the veterinarian will do a complete and thorough physical assessment which may include a lameness examination as well. Radiographs (x-rays) and laboratory tests will be done next. The veterinarian will be looking for an increase in CK, myoglobin, AST, lactate dehydrogenase, BUN, and PCV as well as a decrease in calcium and potassium.
Treatment of Monensin Toxicity in Horses
There is no antidote or cure for monensin toxicity, but the veterinarian may try to absorb the toxin with activated charcoal given orally. The charcoal absorbs the monensin so it can be flushed from your horse’s digestive system. In addition, supportive care, fluid and oxygen therapy can be provided.
This procedure is done by inserting an esophageal tube and administering activated charcoal. The charcoal will find and cling to the monensin so it can be eliminated from the body without being absorbed by the intestines. Your horse will be sedated during this procedure for safety.
Fluid and Oxygen Therapy
Fluids and electrolytes will be given intravenously (IV) and oxygen will be administered through a nasal cannula. This is a tube that has prongs that are inserted into the nostrils and attached to an oxygen supply so your horse can get a constant source of oxygen. Flunixin meglumine may also be given through the IV to relieve inflammation.
Recovery of Monensin Toxicity in Horses
Any damage to the heart may be permanent so your horse’s prognosis is not good if symptoms have already started by the time you obtain treatment. Chronic heart failure may be a permanent complication. It is important to follow the veterinarian’s instructions for homecare exactly and call if you have any questions about the rate of recovery. Additionally, if you have any new concerns, ask the veterinarian for a return consultation.