COW (case of the week): Monensin Toxicity

One of the more sad cases I encountered this week was a horse that was exposed to monensin. If you haven’t yet heard, MONENSIN IS TOXIC TO HORSES! Monensin is an ionophore that is commonly added to cattle and poultry feeds. It enhances the feed efficiency of feeds. This stuff has been being added to cattle feeds for a long time. The fact that is highly toxic to horses is nothing new either. But apparently there are people who have not yet heard.

Fortunately we don’t often see monensin toxicity since it is generally known that horses should never get this stuff. However, apparently not everyone is aware how sensitive horses are to ionophores. In the case I saw this week, the owner had no idea about the toxicity of monensin. What makes these cases so sad is just how much affected horse’s suffer and how easily preventable it is. Symptoms vary based on how much the horse consumes. Symptoms are progressive and typically include abdominal pain, anorexia, sweating, unsteadiness on their feet, stiff gait and/or a reluctance to move. Affected horses often just look like a severe colic. Often they will have a high heart rate and low blood pressure. If a horse survives, they will likely have permanent heart damage that can cause death, weeks or months after the initial exposure.

Unfortunately, there really is not specific a antidote for ionophore toxicity. If caught early enough, we can administer mineral oil or activated charcoal via a stomach tube to slow or inhibit the absorption. Otherwise treatment consists of supportive therapy. Vitamin E and selenium may be of some benefit.

The moral of the story is do not store any feed with an ionophore, like monensin or lasalocid, anywhere near horse feed. If you have any feeds made specifically for cattle or poultry check the labels to ensure they do not have these products added to them. To prevent accidental exposure, products containing ionophores should never be stored in the same location as horse feed or in any location where a horse may gain access to them. Spread the word to all of your cattle friends who may also have a horse.