Ionophore Toxicity in Horses

Ionophores are feed additives used in cattle diets to increase feed efficiency and body weight gain. They are compounds that alter rumen fermentation patterns. Ionophores can be fed to any class of cattle and can be used in any segment of the beef cattle industry. They may also be fed to poultry but are typically toxic to horses.

They are fed to slow the growth of intestinal coccidia. Commercially available ionophores include monensin (Coban and Rumensin), lasalocid (Avatec and Bovatec), salinomycin (Bio-cox and Sacox), narasin (Monteban and Maxiban), maduramicin (Cygro), semduramicin (Aviax), and laidlomycin propionate (Cattlyst). Severity and speed of onset of symptoms of ionophore toxicity in horses is dependent on the amount ingested.

The issues caused by ionophores in horses include cardiovascular issues, digestive upset (colic), muscle impacts (often heart muscle), respiratory problems and sudden death. The lethal dose is less than 1/10th the amount that can be safely fed to cattle. If a horse survives, it will likely have some level of permanent damage to heart muscle, possibly leading to poor performance and congestive heart failure.

Treatment is typically supportive in nature as there is not a specific drug to reverse ionophore poisoning. Prevention is the best option avoiding ionophore poisoning.

Check to make sure that the mill you source your horse feed from is “ionophore free”.

MORE INFO

https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1758-2018.pdf

https://utbeef.tennessee.edu/cattle-nutrition-faq-what-is-an-ionophore/

Thank you Rose Albrecht (QA Expert) for generously providing this content.