Nearly every ranch or farm operation has multiple types of feed around the place. There will be sacks with feed in it for the horses, some for the light calves, some for a steer that’s being fed out, something different for the chickens and some range cubes for the cattle and sheep. Most of these products are harmless if fed to a different animal than intended, but a few can be deadly if fed to the wrong species.
A type of supplement that is used in certain feeds is called an ionophore. Better known by the names Bovatec® and Rumensin®, ionophores are used to improve feed efficiency in beef cattle and to aid in the prevention of some diseases. It’s found in premixed feeds, blocks and in bags for adding to rations.
Bovatec®, with the scientific name of lasalocid, is most often used for cattle in pasture or forage situations and can also be fed to sheep.
Rumensin®, or monensin, is used in feedlots to help prevent acidosis and to control feed intake on high-grain diets while increasing gains in beef cattle. It also helps to prevent coccidiosis in cattle. Rumensin® (monensin) is used in chicken feed also. Rumensin, however, can be toxic to sheep.
The two products, though beneficial for the animals they are meant for, can be very dangerous for horses. Ionophores are a class of drugs that are particularly toxic to horses and it doesn’t take very much to do the damage. Rumensin is ten times more toxic than bovatec and less than one half a gram can be fatal to a horse. They can also be deadly to dogs.
Kadoka, SD, veterinarian Dr. Bill Headlee, DVM, says, “We had a client have nine head of horses get into about a 25 lb bag that was in the back of the pickup. They had scattered it around and eaten some of it. Three of the nine died and it took the others a long time to get over it.”
When horses ingest an ionophore they will demonstrate some or all of the following symptoms: muscular weakness, colic-like symptoms, trouble breathing, lack of appetite, diarrhea, stiffness, lethargy, a blue tinge to gums and membranes (cyanosis), pulmonary edema, degeneration of the heart muscle and kidney damage.
Dr. Headlee says, “The horses that we treated were sweating and at first appeared to be having tying-up syndrome with the stiff muscles and unwillingness to move. They also went into convulsions.”
When a horse survives ionophore poisoning, they can have long term damage, including heart damage which could result in sudden death during exertion weeks or months later. “One horse we treated had muscle weakness and unthriftiness for several years afterward. We attributed that to kidney, heart and muscle damage,” says Dr. Headlee.
Not much can be done for a horse that has ingested an ionophore as there isn‘t an antidote. Dr. Headlee says that one might give the horse mineral oil or activated charcoal to move it through the system faster, in hopes of preventing some of the damage.
Horses are known for being nosey and getting into feed they shouldn’t, as the nine did that Dr. Headlee treated, but it can problems can also occur through cross-contamination of feed. Feed mills are generally very careful to clean out the mixing area before making a different kind of feed, but, even with great care, a small amount of rumensin or bovatec could still get mixed with a batch of horse feed. If that happened, and it was the deadlier rumensin, it could be enough to kill horses that ate the next batch of feed.
Another problem involves the feeding of cattle or sheep feed to horses, thinking that if it’s good for one, it will be good for the other. If a person is going to feed that way, it is critical that they not only read the label carefully but that they talk to the nutritionist that is involved with the feed. If there is any question, it would be good to also have a veterinarian knowledgeable in equines look the label over too.
The safest thing that a horse owner can do is to use feed specifically produced for horses, in a mill that only produces horse feeds. In leiu of that, read labels carefully and check with a veterinarian to be certain.
If a farm or ranch is going to have products on hand with rumensin or bovatec in them, it would be prudent to keep them separate from any other feed and locked up so that horses can’t possibly get into it. Don’t ever put horses in an area where other livestock has been fed anything with an ionophore in it, as horses tend to keep looking for one more nibble of feed after cattle or sheep have quit eating.
The ionophores bovatec and rumensin are good supplements when used properly for the species they are intended for, but, if there are horses and other susceptible species around, there is a responsibility to manage the products so they can do no harm.