With spring finally approaching and horses being turned out to pasture again, we wanted to raise awareness on a couple of plants that are commonly found in pastures (and hay) that can cause issues in the horse.

Please join us over the next few weeks while we go over some of the most common plant toxicities as well as what the signs are and how to recognize the plants.


Ionophores like Monensin (also known as Rumensin), Salinomycin (also known as Biocox, Coxistat or Saccox) and Lasalocid (known as Avatec or Bovatec) are often added to cattle feed and poultry feed, to help improve energy yield from the feed and to help prevent bacterial infections. However, when ingested by your horse they can soon become fatal. 

Horses are 10 times more sensitive to the toxic effects of ionophores compared to cattle. So even ingestion of small amounts of these ionophores can cause serious disease. If your horse ingests one of these products, call your veterinarian immediately as early intervention is always needed!

Ionophore ingestion mostly affects the muscles in the body, including the heart muscle. Ionophores have an effect on the ion balance in the body, which lead to necrosis of the muscle and disturbances in the conductance of the heart. This can lead to increased heart rate, arrhythmias, increased respiratory rate, muscle weakness, mild colic signs and sudden death. Even when horses only show mild or no signs initially, arrhythmias can still be seen later on.

Unfortunately, there is no antidote or specific treatment for ionophore toxicity and prevention is truly the best option.
Treatment is initially directed at limiting the absorbance of the toxic substance into the bloodstream. This is achieved by pumping the stomach to remove any ionophores that might still be present in the stomach. The sooner we can do this, the more ionophores will still be present in the stomach and the more ionophores we can remove from the body. Afterwards, activated charcoal can be administered. Activated charcoal will bind some of the ionophores present in the intestines, decreasing the amount of ionophores that are absorbed into the bloodstream.

After this, the treatment consists of supportive care, which includes IV fluids and supplementation of vitamin E and selenium (antioxidants, known to support healthy muscle). If arrhythmias are present, anti-arrhythmics can be used as well.

If the stomach contents are removed quickly, before significant absorption has occurred, prognosis is fair. If treatment is only started at a later stage, prognosis is poor to grave, with a mortality rate of ~80% due to the effects on the heart muscle.