Disease Du Jour: Thrush and Canker in Horses

Thrush in horses is often underdiagnosed and undertreated, while canker is rare and can be misdiagnosed as severe thrush.
cleaning horse hoof with thrush
Dr. Craig Lesser said environment or conformation can contribute the incidence of thrush. “A horse that is not engaging its frogs or a horse with club feet and deep central sulcus could be more prone to thrush,” he noted.

“Thush is something we commonly see in horses,” said Craig Lesser, DVM, CJF. “It’s an infection in the central sulcus or collateral sulci of the frog. Traditionally, it is a bacterial infection, but occasionally it will have fungal components. And a lot of times horses will have it and it goes undiagnosed and untreated until it becomes an issue.”

He advised veterinarians that “as part of our regular exams, that is definitely something to look into. Whether this horse has a deep central sulcus and maybe has an infection deep within that deep central sulcus that we should treat before it becomes a real issue.”

Lesser is an AFA Certified Journeyman Farrier. He graduated from Colorado State University College of Veterinary Medicine in 2015. Following the completion of an internship at Anoka Equine, he moved to Lexington to complete a podiatry fellowship at Rood & Riddle Equine Hospital and joined the practice as an associate. He is now a shareholder in the practice.

Lesser said environment or conformation can contribute the incidence of thrush. “A horse that is not engaging its frogs or a horse with club feet and deep central sulcus could be more prone to thrush, he said.

“We’ll see thrush in everything from top show horses to backyard horses,” Lesser said.

He reminded veterinarians that owners sometimes get worried because they don’t know that frogs normally slough twice a year. He also said that mild cases of thrush usually don’t cause lameness.

Reddening or extra moisture in the frog can be a tip to inspect the foot closer for thrush, noted Lesser. “Expecially in those feet that have heels that are really contracted, it is hard to see down inside that central sulcus.

Lesser recommended that veterinarians become proficient with their hoof knives and learn how to clean up the frog, central sulcus and the sulci at the heels. When veterinarians see a case of thrush, they should “trim the frog aggressively. I remove any dead tissue or any tissue that could trap bacteria so I have a niche healthy-looking frog.”

Thrush Treatment

Treatment depends on severity. He often uses iodine-based product to dry out the sulci and central sulcus on mild thrush cases. He said there are numerous products on the market. “There are ones on the market that are purple and they stain everything, and it really makes you feel like you are doing a lot,” he said.

With some horses, he starts by soaking the feet with iodine to dry it out. “But the first step is to trim up the foot and get it to the point we can actually treat it,” Lesser said.

In more severe cases with a really deep central sulcus, he starts by cleaning them up.

“A lot of times I’ll take a 4×4 (gauze) and almost ‘floss’ out that central sulcus,” he said. “You’ll be able to fit that 4×4 deep within the sulcus and clean up both edges of it. That does a light debridement on that tissue. Then after that we can add in some iodine.

“If it is deep enough, I oftentimes will pack that area with another 4×4 with some medication on it,” he added. “Some people like to use mastitis medication like Today and Tomorrow. I’ve used some copper sulfate. There’s a whole variety of treatment options with the basis of most of them being drying agents.”

He said severe thrush can make the horse’s foot sensitive and cause some lameness. “Further infection is always my biggest concern,” he said.

When working with a thrush patient, Lesser usually talks directly with the farrier. “I’ll say, ‘Hey, we’re seeing some thrush here. Would you mind opening it up further next time.’ ”

He advised veterinarians to look at the environment at the horse’s facility at every visit. “That’s a huge part of it,” said Lesser. “If these horses are turned out in a big, beautiful field but right by the gate it’s a mud hole, discuss with the owner about changing some of these environmental things.”

Lesser also talked about horses that have ponds in their environments. “Some horses just love to play in the pond and to play in the mud at the side of the pond. Their legs might dry out, but feet just are full of moisture all day.”

The biggest deterrent to thrush, said Lesser, is to pick feet out twice a day. In horses prone to thrush, put something in there to treat thrush twice a day as well.

Canker in Horses

“Canker is hands-down my least-favorite disease,” stated Lesser. “I would deal with laminitic horses all day every day instead of dealing with canker. It’s a tough disease.

“It’s usually midiagnosed,” he said. “Unfortunately, most people think it is really bad thrush. It gets seen by a veterinarian or two and some farriers before it comes to us. We had one slide in veterinary school about it, and it’s something veterinarians may see once in their career. It is very rare to see. Because of that, a lot of times it goes untreated for a little while.”

Lesser said this traditionally was thought to be a disease of draft horses. “I’ve seen it in everything from Thoroughbreds to Quarter Horses to top-end dressage horses to everything in between,” he said.

“What is it? We don’t know,” he admitted. “It was originally thought to be a cancer, and that’s where it got its name from. But since then, there’s been some research that it might be caused by a viral infection from bovine. There’s some people that think it’s a missed bacterial infection. Unfortunately, we don’t have a great answer to the exact cause.”

To diagnose canker, you can take biopsies and send them off, he said. “Usually I diagnose it based on how it looks,” he said. “It will be very white and bleed easily. Most of these horses are not lame from it, but it definitely can cause a lot of bleeding. Often what you hear is that people think they are dealing with thrush but the horse is bleeding randomly and is sensitive to the touch.”

Lesser said canker can invade the hoof wall and make a horse lame, “but initially, it usually doesn’t,” he added.

When looking at a foot, what is the biggest tool in determining if you are seeing thrush or canker?

“My biggest think is [vets] get used to using a hoof knife,” Lesser advised. “Clean the foot up a little bit and see what it looks like. If you scratch on the frog a little bit and it’s thrush, it’s probably not going to bleed much if at all. But if you just sort of ‘bump into’ canker, usually it starts bleeding. The white outer covering of canker is usually a good sign of it as well.”

Collaboration Between Vets and Farriers

“Honestly, being a resource for a farrier is why I have built a lot of my practice,” stated Lesser. “They’re now my larger referral base because they realize I’m not going to throw them under the bus; I’m hopefully going to help them do a better job for these horses and their clients. And at the end of the day, they’re still going to have the clients.”

Lesser said you can offer to take radiographs for the farrier if you are at the barn at the same time. He said if vets see that a horse is acting badly with the farrier, suggest to the farrier and the owner that maybe you could sedate this horse for your farrier because the farrier is “kind of getting beat up.”

“Being that resource is a huge practice builder,” Lesser said. “Most farriers see their clients every four to eight weeks, but you as a young veterinarian might see your clients every year or twice a year. That farrier can instill a lot of trust in you. They can be a practice builder.”

Additional Information

Learn more from Lesser’s conversation on thrush and canker by listening to this episode of the Disease Du Jour podcast.

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