Deadly Feed
By Eleanor Blazer
          "Tainted Feed Kills Horses" are headlines that appear too frequently.   

            Is your horse at risk?  Yes, if you purchase feed from manufacturers that use a drug called an ionophore.

            Ionophores are non-therapeutic antibiotics used to control coccidiosis, a microscopic one-celled parasite, that can infect animals, birds and humans.  Cattle and poultry producers use the antibiotic to fight the protozoa which causes diarrhea, decreased egg production, decreased rate of gain, and death in severe cases.  Cattle growers also use feeds containing ionophores to prevent bloat, acidosis, and to increase feed efficiency.

            While ionophores can be beneficial to cattle and chickens, it can be deadly to horses.  According to a study done in 1985 by Langston VC, Galey F, Lovell R and Buck WB (Toxicity and Therapeutics of Monensin: A rev. Vet. Med., 80: 75), a commonly used ionophore called monensin may cause death in some horses, if as little as 1milligram per kilogram (2.2 pounds) of body weight is consumed.   For an average-sized horse of 1,000 pounds this works out to less than a gram of monensin having the potential to kill a horse.  To put it into prospective, an average-sized paper clip weighs about a gram. 

            One of the first signs that an ionophore may be present in the feed is when horses refuse to eat feed that is new.  Symptoms of ionophore poisoning vary from horse to horse, based on how much they have eaten.  Some horses may die without any clinical signs of being sick.  Other horses may act depressed, have diarrhea, colic, show reluctance to move, be weak or stiff.  Sweating, head pressing, blindness and increased urination may also be present.  Death and/or symptoms usually appear within eight to 24 hours of eating the contaminated feed. 

            It is difficult to diagnose ionophore poisoning.  The symptoms are similar to several other equine diseases.  Only testing the feed or stomach contents can confirm the presence of the ionophore. 

            Treating a horse poisoned by an ionophore depends on diluting the drug that is in the body and getting it out of the horse has quickly as possible.  This is usually done by the veterinarian administering fluids.  Sadly, even this is not usually effective, and the odds of saving the horse is low.  Horses that do survive generally have heart damage and can no longer be productive. 

            Despite feed companies having strict guidelines in place when handling ionophores human error can occur.  The only way to prevent horses from being exposed to ionophores is to purchase feed from companies which do not use the drugs.  Horse owners who also feed cattle or poultry need to avoid using livestock feeds that contain ionophores, or keep them in a separate facility away from the horses.  Ionophore drugs are: monensin, lasalocid, salnomycin, narasin, maduramicin, laidlomycin and semduramincin.

            There is no antidote for ionophore poisoning, so it is up to you to ensure your horse is safe. 

* Earn a Bachelor of Science Degree in Equine Studies, an Associate of Arts Degree in Equine Business Management, or certification as a Professional Horse Trainer, Riding Instructor or Stable Manager.  Go to and get started today! 

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