Monday, November 25, 2013

Blastomycosis, Botulism, Monensin: Things Horse Owners Should Know About

Happy Monday, folks. Today's blog was requested by several different readers, because they felt that all horse owners should be aware of these frightening problems.

Let's start with...


What is it?
Monensin is a very widely-used antibiotic, commonly sold under the brand name Rumensin, made by Elanco. It is available without a prescription.

Where is it?
Monesin is available from most feed mills, and gets mixed into many feeds.  It gets added to the feed of dairy cows, beef cows, turkeys, chickens, and sometimes pigs.It also gets added to mineral blocks, and sometimes even water tanks. While humans only take antibiotics to combat infections, factory farmers (and somtimes smaller farmers) commonly pour antibiotics into their animals' daily meals. Because their animals are packed together in small spaces, infections such as coccidiosis spread easily. The farmers use antibiotics to try to prevent this kind of thing from happening. Monesin comes in powder, paste, pellet & injectible forms and in molasses- based mineral blocks for cattle.

Why is it scary?
  • Monensin is fatal to horses
  • It only takes a few grams to be poisonous.'
  • There is no really effective treatment.
  • It can cause death in less than 24 hours.
  • I can cause death even weeks after ingestion.
  • It's incredibly common, found in many livestock feeds.
You might remember the terrible case in 2003, where the Huston family lost 12 of their prize Belgian pulling horses to Monensin poisoning. A feed mill in Cottage Grove, WI had accidentally mixed a small amount of the antibiotic into the farm's horse feed order. There was another case in Michigan during the late 80s, with hundreds of horses affected. Those are only two of the most famous cases in this area-- Monensin poisoning is the most common cause of poisoning in horses.

What are the symptoms?
Colic, sweating, laying down, irregular heartbeat, difficulty breathing, peeing a lot, refusing to eat, abdominal pain.

How Can I Avoid It?

Of course not all cattle feed and chicken feed contain monensin, and when they do contain it, it may be present in small enough amounts to be safe... but rather than attempt to check ingredient labels for drug names and percentages, just stay safe and give your horse only horse feed! If you get your grain mixed by a local feed mill, be sure you ask them about the precautions they take to avoid cross-contamination. Remember, it only takes a few grams of Monensin to be poisonous!

You should also avoid the following drugs which have the same effects: lasolacid (Bovatec), laidlomycin, narasin and salinomycin. Although much less common, they are equally deadly.

Find out more at these links: Ionophore Intoxication in Horses,     Monensin in Horses, a Deadly Combination,    Monensin: Poison for Horses,    Poisoning in the Feed Room.

Up next, we have...


What is it?
"Blasto" is a fairly rare fungal infection that can enter the body through the lungs or open wounds. The fungus then spreads, slowly killing its host. The fungus can affect just about any animal, including horses and humans, but is most common in dogs.

Where is it?
Blastomycosis is most often found in areas where the soil is full of decomposing organic material habitually moist. The shady soil in the woods of Northern Wisconsin, anywhere near the Great Lakes and other large bodies of water, and river valleys are all places where it pops up. The fungus is usually only encountered when it is disturbed from its environment-- like when a horse rolls or paws, a dog digs or noses through the forest soil, a wood pile is moved, etc.

Why is it scary?
"Blasto" is most frightening because it's so easily misdiagnosed, or not diagnosed at all. Since it's fairly rare, your vet may not be familiar with it. This is particularly bad, because the fungus needs to be treated early, especially if it is in the lungs, for a patient to survive. Dogs and horses have lost eyes, died gasping for air, or simply suffered for years while vets and owners remained puzzled.

What are the symptoms?
Just about anything, unfortunately. If the Blasto fungus gets in through the lungs, it can produce coughing, fever, chest pain and nose mucous. However, some patients have had no symptoms, other than a mildly reduced breathing capacity. If the fungus gets in through a wound, it can then travel to the lungs. I can also promote infections in the wound that disguise the Blasto. In one case, a mare with an infected teat suffered from, and was treated for, simple mastitis for months before skin lesions finally appeared on her abdomen and Blasto was diagnosed. These random skin lesions look scabby and grainy, and can appear anywhere on the body, regardless of where the fungus originally entered. These lesions can also occur internally, on bones and organs, creating symptoms that may look like the symptoms of other diseases entirely, such as kidney malfunction. Blastomycosis can also cause weight loss, enlarged lymph nodes, inflammation in the eyes and a general feeling of sickness and fatigue.

How can I avoid it?
Humans can avoid Blastomycosis by wearing a mask when working in musty, moist, organic environments, and by only working in these environments in dry summers or in winters, when the fungus is dormant or dead. As for animals... keep their pastured cleaned up, don't let them dig and roll in moist, woody areas, and pray.

Read more at these links:  Treatment and Outcomes for BlastomycosisSystematic  Blastomycosis in a Horse,    Blastomycosis Disease Fact Sheet.

The next sickness was recently brought up by many horse owners after they saw this Craigslist ad, which described 19 sick or dead horses in Vienna, Georgia.

Click to Enlarge


What is it?
Botulism is a very potent bacteria which can kill many animals, including humans, in a few days. Horses are particularly affected by it. It is colorless and odorless.

Where is it?
Although Botulism bacteria can enter a wound, it is most commonly eaten in contaminated hay or haylage. Grain is less often contaminated, but can be affected, especially wheat. We used to believe that food had to have had contact with a decomposing animal in order to be contaminated. Now we know that in fact, Botulism can grow in any low-oxygen environment. Canned food, silage and dense round bales of hay are examples of this.

Why is it scary?
By the time a horse shows symptoms of botulism, it's very hard to treat. Since the horses become paralyzed, they must be held up by a sling. Since they cannot swallow well, they must get IV fluids. At this point, prognosis is poor. Every hour that a horse remains untreated for botulism greatly reduces its chances of survival. Unfortunately, it also takes days for tests to diagnose botulism.

What are the symptoms?
Muscle shaking, difficulty eating, slow movement, weakness, loss of tail and eyelid tone, respiratory failure. Because of their weakness and difficulty eating, horses with botulism may drool quite a bit, even through their noses. Inhaling this drool can cause pneumonia.

How can I avoid it? 
If you can possibly avoid doing so, do not feed round bales of hay. Never feed haylage or other kinds of silage to horses. Buy hay and grain only from reputable companies. Horses can also receive a botulism Type B vaccine... but this vaccine does not prevent types A or C botulism.

Read more at these links:  Botulism in Horses,   Botulism in Horses and HaylageBotulism in Horses: An Update,    Grain Test for Botulism,    Botulism May Become a Problem in Horses This Winter.

Bonus: Check out this Home Canner's Guide: How NOT To Die From Botulism.


  1. Rumensin is pretty common around here. It is well known to kill horses and people are careful with it. I have been lucky never to have had to have it anywhere near my horses.
    I get so offended, as a rancher/farmer, every time we are accused of pouring antibiotics to the cattle to fatten them. I have never done such a thing and don't know anybody who has, or so I have always said. Apparently I was wrong. Rumensin is occasionally added to cake, cattle feed, think horse cookies for cattle and a yummy snack for horses too, when not containing Rumensin. I had no idea, and don't know that the people I know who have fed it knew, that it was an antibiotic. That was a lot of knows :)
    The feed mills say that it will help keep the cows fat. It is also said, not by the feed mills, that it will burn up their gut and kill your cattle off quicker.
    I have never fed it, personally, and never will if it is up to me and not just because of the horses anymore.

  2. Last summer my Lab puppy Kasey died of Blasto. She was 7 months old. We took her into the vet when we saw her acting lethargic and after taking some X-Rays they found odd O shaped masses in her lungs. They took a blasto test and a week later we got the call that she had tested positive and her case was too far along for medication to make a dent in the damage that was done. We had to put her down the next day. Losing her was one of the worst things that has ever happened to me. Blasto is something I hope I never have to mess with again. It was a truley traumatizing experience.

    1. I'm so sorry. Thank you for sharing your story though-- it may help others protect their pets.