BOTULISM IN HORSES. (Beware of birds using your trough.)

Yesterday, I wrote about our ravens and how happy I was that they had come back.

Today, I received a very smart warning from a reader (Thank you).  I knew that I had to pass it onward.

“I have to warn you about something that happened to a friend of mine. The ravens are scavengers (like vultures), and had eaten road kill and then drank from my friend’s water trough for the horses. The horses came down with botulism. 4 died awaiting diagnosis, and the other 3 were euthanized because they were too far gone. There was an actual investigation, and this was the determination of the wildlife officers and veterinarians who worked on the case.
These are smart birds, and you can “train” them to stay away from the horses. Set up their own area away from the horses (with water, and food, if you like), and then aggressively shoo! them away from the horses, and leave them alone when they stay in their own area. It is amazing how smart they are.
But don’t take a chance with them drinking from your horse’s water troughs. My friend’s horses died excruciating deaths (blindness and paralysis).
When they are around, as a precaution use bleach and clean your water buckets every day.”

So, I decided to do some research.


Botulism is violent and almost always fatal in horses.  A dose that wouldn’t bother a dog or a cow, will kill a horse.

Ask your vet about a vaccine.

Botulism can be found in the soil, in hay and in troughs… best to keep troughs clean from bird droppings, your hay dry (and off of the dirt) and your horses vaccinated.


I found this article in Equus online.  You can go to the original article here.

Click image to go to the original article

Botulism in horses is a nightmare no one wants to face: Last night your horse was his usual cheerful self. This morning, you find him standing alone with muscle tremors, his head low and his lips slack, drooling heavily, too weak to manage more than a shuffling walk.

Botulism in horses is a devastating illness that occurs when they ingest toxins produced by the Clostridium botulinum bacteria. The resulting disruption of communication between nerves and muscles leads to debilitating and potentially deadly neuromuscular impairment. Without prompt treatment, botulism in horses is almost always fatal.

No hard figures are available, but Robert Whitlock, DVM, PhD, of the University of Pennsylvania School of Veterinary Medicine, estimates that roughly 150 to 250 horses succumb to botulism poisoning each year. Most cases occur in states east of the Mississippi, but it can happen virtually anywhere. Complicating matters is the fact that botulism can be difficult to recognize. “It’s a rare disease and unfortunately, practitioners without experience dealing with botulism have difficulty properly diagnosing it,” says Whitlock. A horse’s chances of survival depend on how quickly treatment begins and how rapidly the disease signs progress.


Which makes it important to understand how botulism poisoning occurs, what it looks like, what can be done to treat it and–perhaps, most critical–what you can do to reduce your horse’s risk of exposure to the causative organism. Here’s what you need to know.

It’s impossible to completely avoid C. botulinum bacteria.
C. botulinum spores are found in the soil, on vegetables and foods–they are literally everywhere,” explains Whitlock. “Inert spores can live in the environment for decades without causing any harm. It is when they are given a favorable environment for toxin formation that they pose a danger.” Botulism spores are most likely to form toxins in moist, anaerobic (with little or no oxygen) conditions where protein is rich and acidity is low (pH greater than 4.5). A prime location is decaying vegetable matter. More rarely, toxins may form in decaying animal tissues.

Various strains of C. botulinum are capable of producing seven different neurotoxins (A through G), not all of which can sicken horses. Most cases of equine botulism are caused by type B toxin, which can be found anywhere but is most prevalent in the Northeast and the Appalachian states.

Equine illness linked to type C toxin has been reported in Florida, California, New Mexico, Utah, Arizona, the New England states and Canada. Type C toxin is usually associated with decomposing animals but is also in bird droppings. A third form of the botulism toxin, type A, is found in soil in the northwestern states of Washington, Idaho, Montana and Oregon as well as Utah and Ohio. Type A toxicity is uncommon in horses.

Horses are especially sensitive to C. botulinum.
“A dose of botulism toxin capable of killing a horse probably would not make a cow or a dog sick,” explains Whitlock. “Horses are much more susceptible as a species. Even humans are more resistant than horses.” Evidence in literature suggests that vultures, due to their subsistence on carrion, have developed a natural resistance to botulism.

C. botulinum can affect horses in three ways:

  • The term “botulism” most often describes poisoning that occurs when horses ingest the preformed toxins present in hays or feeds contaminated with the active bacteria.
  • Intestinal toxicoinfection, also called “foal botulism” or “Shaker foal syndrome,” develops when a foal ingests C. botulinum spores, which vegetate, colonize and release toxins in the immature gastrointestinal tract. “[This] risk declines about the time the foal is weaned and the mature microflora of the gut prevent the overcluster of C. botulinum,” says Nathan Slovis, DVM, DACVIM, of Hagyard Equine Medical Institute in Lexington, Ky.
  • Wound botulism, the rarest form, results when C. botulinum enter a wound that closes over quickly–such as an injection site or puncture wound–providing an anaerobic environment that enables them to become activated and multiply. Castration wound infections and umbilical hernia repair with clamps have both been associated with wound botulism in horses.

Botulism toxins are among the most potent in the world.
Botulism toxins can permanently damage the nervous system. They travel through the horse’s bloodstream, eventually reaching the myoneural junction, where signals pass from motor neuron to muscle fiber. After penetrating neuron cells, the toxins bind to the synaptic vesicles, sacs that contain the molecules (acetylcholine) that signal the muscle to contract. This prevents the chemical’s release, and the result is paralysis.

“Essentially, the toxin disrupts the communication from nerve to muscle,” says Pamela Wilkins, DVM, PhD, professor of medicine at University of Illinois College of Veterinary Medicine. “It’s like cutting a telephone line. The signal is still coming in, but when you pick up the line, there’s nobody there.”

The toxin’s effects are seen first on the horse’s most frequently used muscle groups: those used for chewing, swallowing, standing, blinking and swishing the tail. “Typically you see tongue tone weakness, eyelid and tail weakness, an inability to eat normally, a stiff, short gait, trembling and increased recumbency,” says Wilkins. “But clinical appearance depends on the dose of the toxin. Some horses won’t eat and are a little weak and that’s as bad as they get; others are down and paralyzed.”

Signs may appear anywhere from a few hours to several days after exposure to the toxins. Death, says Wilkins, is usually due to suffocation when pulmonary muscles are compromised.

Feeding round bales increases a horse’s risk of developing botulism–but not for the reasons you might think.
Most of us have heard that the rotting bodies of rodents, birds or other wildlife swept up during the hay baling process are a major source of botulism poisoning. But this simply isn’t true.

“That is an all too common misconception,” says Whitlock. “The truth is that 90 percent of botulism cases are in no way associated with dead animals. Most horses have type B botulism and that comes from soil, not from deceased animals [which are linked to type C].”

In fact, “the spores are [in the hay] all the time, whether they are picked up during harvest or baled along with the flecks of dirt with the grass. If the hay remains dry, then it’s fine. But if you have enough botulism spores with an anaerobic environment and spoilage in this tightly packed bale, the spores grow and make toxins,” says Whitlock. “That’s especially true when the bale is thrown out in a field or even stored in a shed but on the ground where dirt and moisture can get in.”

A less common and often overlooked source of botulism poisoning is loose hay thrown out onto muddy or damp ground in paddocks or other enclosures: “The horses will stomp on it and the hay gets packed down,” says Whitlock. “By the time the horses come back and dig it out of the mud, the environment is conducive for spores in the soil to form toxins.”

The swiftness of onset and severity of botulism signs are good predictors of a horse’s prognosis.
The greater the amount of botulinum toxin a horse ingests the worse his illness is likely to be. And the sooner a horse is given botulism antitoxin, the better. The polyvalent antitoxin (which works against both type B and C) and a monovalent antitoxin (against type B) contain antibodies that bind to the free-floating toxins in the blood that would otherwise attach themselves to neurons. But the antitoxin cannot repair the damage already done to neurons.

“The antitoxin does not reverse clinical signs, it abates the progression of them from that point on,” says Whitlock. “If the horse is already down, or very weak and approaching that point, it’s too late.” Once the antitoxin is administered, the body can begin the process of growing new nerve cells.

In addition to the administration of antitoxin, horses with botulism often require intense supportive care, which usually consists of antibiotics, intravenous fluids, catheterization and rectal evacuation. Bedsores from long periods of lying down, corneal ulcers due to poor eyelid tone, and pneumonia from insufficient respiratory activity are among the most common complications.

The total cost of care and treatment for a horse with botulism typically ranges from $10,000 to $15,000, depending on the length of hospital stay. Affected horses may not recover their full muscle strength for six months or longer.

A small percentage of affected horses survive without treatment, says Whitlock, “but only when they’ve had a low dose of toxin and the clinical signs are very slow and gradual over a period of days.”

Laboratory tests can confirm botulism, but results may be available too late to matter.
Botulism is confirmed using a mouse inoculation test–also called mouse bioassay–which can detect toxins in serum, manure or gut contents. A diluted sample is injected into mice and they are observed for signs of botulism. If they are affected, more samples and specific botulism antitoxins are injected into other mice, which are observed for clinical signs to determine the type of botulism poisoning.

The test can take five to 10 days and may be inconclusive if the amount of toxin from the sample is insufficient. That’s why, says Wilkins, most cases of botulism are diagnosed based on clinical signs alone: “We’ll use lab tests as confirmation, but by the time the results are in, [a horse with botulism] is either better or isn’t alive anymore.”

Nonetheless, she adds, signs can be subtle and easily confused with other illnesses. “Botulism can present like colic,” says Wilkins, “and it has been confused with severe renal failure.” In addition, botulism poisoning in horses can also look like rabies, Eastern equine encephalomyelitis, West Nile encephalitis, equine herpesvirus and plant toxicity.

The most effective way to prevent botulism is through vaccination.
Available since the mid-1980s, the equine botulism vaccine is effective against toxin type B, the most common form in horses. Statistics show that the inactivated toxoid vaccine is effective in about 95 percent of cases, and even when protection is incomplete it can increase a horse’s chances of survival.

The American Association of Equine Practitioners recommends botulism vaccination of pregnant mares and of foals, primarily to prevent Shaker foal syndrome.

Whitlock, who describes the vaccine as “one of the safest and most efficacious in the industry,” strongly advises administering it to horses who are fed round bales as well as those in areas where previous cases of botulism have occurred. “I can’t tell you how many times I hear, ‘My vet never told me about this [vaccine],'” he says. “This is a situation where an ounce of prevention is worth a pound of cure.”


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5 comments have been posted...

  1. Dave Miller

    Hi Guys

    Here are the current top 20 individual standings as well as the top 10 team standings after day two of the Jumping

    As well as the current overall medal standings. Some nations are doing better than expected, and unfortunately some are doing slightly worse. Have a look to see how your country is fairing.

    Remember you can get TV times for the USA and UK as well as find out how you can stream all the live action at the link below

    Please let me know if these comments are getting too much :) Would like to join the web community but not get on their nerves.


  2. Bunny

    There is another bird problem to watch out for and that is when a bird poops, or – worse – drowns and dies in a water trough or bucket. Birds are heavily infested with salmonella. A horse drinking out of a trough or bucket where a dead bird has been stewing (as in a warm environment), or where there is a lot of contamination by bird feces as in a bucket or water trough that has not been cleaned recently, may ingest enough of the pathogen to create a cascade of toxic events bad enough to cause horrific illness if not death. Symptoms of salmonella poisoning are similar to those of Potomac Fever (some of you may remember THAT epidemic from decades ago!). Unfortunately the treatment for salmonella poisoning is not the same as for Potomac Fever and the two diseases are so similar that vets may mistake one for the other and the wrong treatment method also will hasten a horse’s death exponentially. Prevention is the best way to make sure a horse does not drink contaminated water and suffer the consequences. I well remember this from a boarding barn I was in at the time and the barn manager nastily stating that she was sure she “couldn’t monitor and clean and refill water troughs every day.” After witnessing the horrible suffering and death of a top competition horse in that barn most of us left that facility and I understand that a few months later the place was closed down. Moral of the story is if you can’t provide the most basic essential for your horses – clean fresh water, every single day – you shouldn’t have a horse or especially not hold yourself out as a safe boarding facility!

  3. JKMcCandless

    Thank you so much for sharing this valuable article on botulism. It is another thing to worry about, but great to be aware of. I appreciate your articles very much. Jeannie

  4. Dave Miller

    Hi there fellow riders

    Here are the results from yesterdays first day of Showjumping.

    As well as the current overall medal standings. Some nations are doing better than expected, and unfortunately some are doing slightly worse. Have a look to see how your country is fairing.

    Remember you can get TV times for the USA and UK as well as find out how you can stream all the live action at the link below


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