What You Should Know About Horses and Monensin Poisoning

by Caitlyn Andrews August 29, 2018

What You Should Know About Horse Monensin Toxicity

Have you heard of monensin? You need to know about this feed additive if you have horses.

It could save your horse's life.


What is monensin?

Monensin is an ionophore antibiotic. You may have heard of monensin referred to by its common trade name - Rumensin.

It's a feed additive commonly used for cattle. It can improve feed efficiency and increase milk production efficiency. It also prevents and controls coccidiosis. 

Coccidiosis is one of the most economically devastating diseases in the cattle industry. It causes diarrhea, weight loss, dehydration, loss of appetite, and in some cases, death.

Cattle producers have successfully used monensin for decades to keep their herds healthy.

Why is monensin poisonous to horses?

If monensin is so beneficial for cattle, why does it harm horses?

Horses are highly sensitive to ionophore toxicity. Monensin disrupts the transportation of sodium and potassium in cells. Consuming even small amounts of monensin can lead to heart failure and can be lethal for horses.

How can horses get into monensin?

You might be thinking that your horse could never get into monensin because you don't have cattle. Of course, horses that live on the same farm as cattle or share the same barns or pastures are at a higher risk.

However, horses can still accidentally ingest monensin without having a cow as a pasture buddy. If you've ever hauled your horse to another farm, practice arena, sale pen, or another unfamiliar place where cattle could have been then your horse could come into contact with cattle feed.

A nosy horse could find some spilled pellets on the ground or leftover in a bucket. Pay attention to your horse and don't let them eat any leftover grain that they find.

It's not just cattle feed you need to watch out for. Monensin is sometimes used in swine or poultry feed. Be cautious and don't let your horse near any feed intended for another species if you are unsure of whether or not it's safe for horses, too.

Even if the feed isn't for another species, it's possible for horse feed to be contaminated with monensin at the plant where it's made. This is why it's important to buy feed from reputable feed mills or manufacturers.

Symptoms of monensin toxicity in horses

Horses that have eaten feed with monensin can show a variety of signs. It all depends on the individual horse and how much monensin has been consumed.

If you suspect your horse has ingested monensin, you should contact your vet immediately. Symptoms typically appear within 12 - 24 hours after the horse has eaten monensin.

Here are some of the symptoms of monensin poisoning in horses:

  • Colic
  • Increased heart rate
  • Abdominal pain
  • Muscle weakness
  • Dark urine
  • Sweating
  • Incoordination
  • Diarrhea
  • Rapid breathing
  • Inability to stand
  • Abnormal movement
  • Heart failure

Horses may exhibit signs of congestive heart failure after the episode. Sudden death can occur anytime in the weeks or months that follow the incident.

Treatment for monensin poisoning

Unfortunately, there is no cure for monensin or rumensin poisoning in horses.

There is no vaccine or magic pill to make it go away.

The best way to stop your horse from suffering monensin poisoning is to prevent it from happening in the first place.

No matter how careful you are as a horse owner, we all know that accidents can happen. A stubborn pony can break out of his stall and open up the feed bins or a mix up at the feed mill could cause monensin to get into your horse's feed.

If your horse ate monensin, try not to panic. Though there is no definitive treatment, it's possible that your horse will recover. If you catch it early, your vet can try to treat the symptoms or administer supportive care.

Often, this done by using activated charcoal or clay products. Your vet may administer these via an esophageal tube. These products absorb the toxins so they can be eliminated through the digestive system instead of being absorbed into the intestines. Your vet may also try administering fluids and electrolytes through an IV.

Horses exposed to monensin can develop permanent heart damage. Even with prompt treatment, it's possible for the horse to pass away weeks or months down the road from heart failure.

This is why it's crucial that you enlist the help of your vet as soon as possible. Be sure to follow any aftercare instructions that are given. Monensin toxicity is serious and you should never assume that your horse will just recover on their own without any help from you or the vet.

Tips to keep your horse away from monensin

Here are some tips for keeping your horse from getting monensin poisoning:

  • Store cattle, swine, poultry, and other feeds separately from horse feed in clearly marked containers;
  • Use separate feed tubs, troughs, or buckets for horses if you have other animals on your farm;
  • Lock or secure feed bins to keep an escaped horse from opening one and helping themselves to a snack;
  • If you have multiple animals and someone is carrying for your horse, be sure to go over the importance of keeping the feeds separate and not allowing your horse to try the other feeds;
  • When traveling to areas where other livestock have been present (rodeos, sales pens, etc), don't let your horse pick at feed tubs or buckets. Keep an eye out for loose pellets on the ground;
  • Purchase quality horse feeds from a reputable feed store or manufacturer to reduce the risk of contaminated grain;
  • Monitor your horse closely and always look for signs of distress or discomfort when caring for them;
  • Keep your vet's emergency phone number handy and posted on your horse's stall or elsewhere in the barn so you or someone caring for your horse can easily reach the vet if needed.

Better safe than sorry with horses and monensin

Monensin poisoning can be devastating for horses. This is why it's important to always make sure your horse can't access livestock feed with monensin.

Follow the tips above and never hesitate to contact your vet if you believe your horse has gotten into feed with monensin, even if the horse isn't showing symptoms yet. Prevention and fast action could save your horse's life.

Caitlyn Andrews
Caitlyn Andrews


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