Ionophores are feed additives commonly used in cattle diets to enhance feed efficiency and promote weight gain. These compounds work by modifying rumen fermentation patterns and can be administered to all types of cattle, making them versatile across various segments of the beef industry. Like many other feed additives, ionophores are provided in small quantities and are typically delivered through another feedstuff as a carrier to ensure proper intake. In addition to their efficiency benefits, ionophores help reduce the occurrence of coccidiosis, bloat, and acidosis in cattle.
Ionophores are TOXIC to horses and equines. Horses are extremely vulnerable to ionophore toxicity, with a lethal dose being less than one-tenth of what is safely fed to cattle. For example, just 2-3 mg/kg, or roughly 1 gram, of monensin can poison a 1,000 lb. horse. Salinomycin is even more dangerous, with only 0.6 mg/kg needed to cause fatal poisoning. Even a tiny amount of ionophore can be deadly to horses.
Symptoms
The severity and rapidity of clinical signs depend on the amount ingested. Horses sharing the same feed source can be affected at the same time.
Common signs include:
- Sudden death
- Exercise intolerance
- Refusal to eat
- Colic
- Increased heart and respiratory distress
- Hypotensive shock.
It’s important to note that if a horse survives, it will likely suffer some degree of permanent heart muscle damage, which could result in poor performance and potentially lead to congestive heart failure.
Treatment
There is no specific antidote for ionophore poisoning, but supportive care might be beneficial depending on the severity of the case. This care includes emptying the gastrointestinal tract with mineral oil and activated charcoal, along with administering IV fluids to support heart function. In more serious cases, intensive nursing care may be needed, including heart monitoring and the use of antiarrhythmic medications.
Prevention
Understanding how your horse’s feed is produced and what it might come into contact with is crucial for safeguarding their health. Knowing the production process helps you ensure that the feed is free from harmful contaminants, such as ionophores, which can be deadly to horses. It’s essential to choose feed suppliers who prioritize safety and transparency, and who implement rigorous protocols to prevent cross-contamination, especially when manufacturing feeds for different species. By staying informed and selecting trusted sources, you can significantly reduce the risk of accidental poisoning and protect your horse’s well-being.
You might have seen a post on Facebook about Beutler Ranch in Oklahoma losing a majority of their herd to monensin poisoning (below), from horse feed that was accidentally treated with the drug in the feed mill. It is a heart-breaking and developing story. This is just one sad tale of a mix-feed mill accidentally sending horse feed out with the ionophores in the feed.
References
The University of Arizona: https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1758-2018.pdf
Kentucky Equine Research: https://ker.com/equinews/ionophore-toxicity-horses/
UT Beef & Forage Center: https://utbeef.tennessee.edu/cattle-nutrition-faq-what-is-an-ionophore/
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