There’s No Easy Way to Treat Cushing’s Disease

Senior horses may have multiple issues that affect trimming and shoeing strategies, from old injuries to arthritis that limit range of movement or the ability to hold up a hind leg. But the one condition that can most frustrate the owner-vet-farrier team is Cushing’s disease.

Cushing’s, also known as pituitary pars intermedia dysfunction (PPID), is a metabolic disorder common to older horses.

Cushinoid horses often have long, curly winter coats that shed incompletely or late. These horses may show weight loss, excessive drinking and excessive urination. They can develop degenerative suspensory ligament desmitis (DSLD), recurrent infections and, perhaps most importantly and commonly, laminitis.

Cushing’s disease1 occurs when the pars intermedia portion of the brain secretes abnormal hormone levels. These hormones in turn produce high levels of adrenocorticotropic hormone (ACTH), which stimulates the adrenal gland to produce cortisol, a stress hormone. However, the exact mechanism of Cushing’s disease is not completely understood in the horse, and hormone responses in these horses can be inconsistent.

Diagnosing And Treating Cushinoid Laminitis

To the farrier, laminitis typically is the most relevant result of Cushing’s — and often the most frustrating.

The exact process of laminitis development in these horses is unknown. However, it could be associated with insulin resistance. Persistent hyperglycemia (high blood sugar) is a common finding in horses with Cushing’s.

Diagnosis is made based on clinical signs and history, as well as blood test results. Since horses with Cushing’s may produce different hormone levels, and often are inconsistent with each other, veterinarians may use one or more blood tests to reach a diagnosis. These tests may include a basic blood profile — complete blood count (CBC) and chemistry panel, an endogenous (resting) ACTH test, a dexamethasone suppression test, resting insulin and/or glucose levels.

Treatment involves both medicine and management. These horses require diligent care including attention to teeth, deworming, vaccination, nutrition and, of course, farriery. The most commonly used medication is pergolide, licensed in the United States as Prascend. The pergolide dose required to treat an individual horse may change over time as the disease progresses, so the horse should be monitored regularly by a veterinarian. Cyproheptadine is also sometimes used to treat Cushing’s disease in horses, but the results are more variable than with pergolide.

Because Cushing’s disease is an ongoing and progressive condition, even with appropriate therapy, these horses can be medically and financially challenging to manage.

Lexington, Ky., veterinarian and farrier Raul Bras of Rood and Riddle Equine Hospital says that laminitis in Cushinoid horses can be particularly frustrating.

“You do a lot with their feet,” he says, “and when everything looks the way it’s supposed to look, you still can’t get the horse comfortable.”

Hewitt, Texas, veterinarian Bob Judd agrees saying that laminitis in horses with Cushing’s is “tremendously more difficult to treat than laminitis from other causes.”

Bow, Wash., farrier Shane Westman has seen the same thing among his clients’ horses.

“Cushinoid laminitis is harder to manage,” he says, “because they’re prone to it again.”

As with any laminitis case, treatment of the underlying cause is critical to managing the feet, say all three professionals.

“You have to have control with what’s going on with their metabolic system,” says Bras, noting that often Cushing’s horses don’t respond to trimming and shoeing therapies in the same ways as other laminitic horses.

“It is difficult to get complete control of the disease,” Judd says. “To solve the underlying problem is critical. With other causes, if you can treat the underlying problem and get them through it, generally you’re in good shape. But Cushing’s is there forever. And it’s progressive. It will keep getting worse.”

Working As A Team

Westman stresses the importance of working with the client and the veterinarian to ensure that the horse is properly managed.

“Ignorance is the biggest problem I deal with,” he says. “Although there’s a lot of information out there, there’s not a lot of great information.”

Westman says that he feels dietary management is critical with these horses. He worries that owners may fall victim to misinformation or untested products.

“There’s a lot of supplement companies going after that,” he says. “There’s a lot of these ‘miracle’ supplements and people jump on that. I’m an evidence-based guy.”

Westman recommends close cooperation between owner, veterinarian and farrier to manage these horses.

“I think we need to get the vet and the farrier together a little bit better in educating the client on these things,” he says. “A lot of times a proper feeding program hasn’t been stressed. We need to maintain the horse as best we can so that we don’t have issues. That’s the vet’s department. I’m the technician in this process. But the client looks to both of us for advice.”

Judd confirms the importance of dietary management.

“Not every Cushing’s horse is insulin resistant,” he says. “About 50% of horses with Cushing’s also have metabolic syndrome, and those horses are even more difficult to deal with and more expensive. The owner has to be so tedious at feeding them properly.”

Judd points out that insulin-resistant Cushing’s horses require a diet of less than 10% non-structural carbohydrates with no pasture initially, but “maybe a grazing muzzle down the road.”

“They are difficult management-wise,” he says.

Bras agrees with the importance of metabolic and dietary management for these horses.

“You try to control them,” he says, “with medication and checking blood levels.”

However, timing of Cushing’s-related laminitis, while often seasonal, may not be what one would expect.

“One of the other issues I’ve been having with Cushing’s is that we always think spring grass with laminitis,” he says. “But even during the fall, I’m seeing a lot of these Cushinoid horses having episodes of laminitis.”

Bras thinks that these seasonal flare-ups may be related to the impact of season and daylight on equine hormones.

Westman also sees a significant seasonal impact on laminitis in Cushing’s horses.

“I think the fall is actually worse than spring,” he says. “In the fall, the grass seems to sneak up on you.”

Westman notes that weather extremes can stress the grass, increasing sugar levels in the pastures. He has one piece of advice for owners with insulin-resistant and Cushing’s horses: “Grazing muzzle!”

Greater Risk For Relapse

Even when owners are diligent about sticking with a program of medical and environmental management, these horses can prove challenging for the farrier.

“At some point they always relapse,” Westman laments. “Cushinoid laminitis is harder to manage because they’re prone to it again. If you have an acute episode (of laminitis) in a younger horse, sure you have to look at it, but it’s not as bad as when you know that every year in the fall and spring they’re going to relapse.”

Judd agrees.

“With a horse foundered from other causes, once you get them through it and they’re stable, you’re fine in most cases,” he says. “Cushing’s horses, they’re never fine.”

Judd says he spends a great deal of time counseling owners about realistic expectations with these horses.

“You’re looking at a lot of long-term control, a lot of X-rays, a lot of corrective shoeing and meds — for the rest of the horse’s life,” he says. “Cushing’s will keep getting worse. And pergolide is expensive. It’s medically and economically difficult.”

Bras finds that these horses are also slower to respond to appropriate trimming and shoeing than other laminitic horses, and may not respond at all as expected.

“With other horses, you do something, and they’ll respond in a couple of days,” he says. “With some of these Cushinoid mares it takes me a week or 2 weeks to get a response. These horses are aged. Their body doesn’t seem to respond as well as it did before.

“They have so many different issues. It’s a multifactorial cascade on the system. Laminitis may be the obvious, but they have so many other things in their system that it doesn’t help them get over the hump. I think sometimes with the underlying cause, their system gets so out of whack that no matter what you do with their feet you can’t get the inflammation and pain under control.”

Bras says these horses test the extent and breadth of his expertise.

“Shoeing-wise,” he says, “you use everything you have in your toolbox — boots, wooden clogs, glue-on shoes and nylon shoes.”

Sometimes Bras finds himself reaching for solutions beyond the obvious or proven.

“There are some cases,” he says, “where I find myself using ice even though it was thought to be used only on acute laminitis cases.”

Bras finds pain management with these horses challenging. He notes that some horses seem to respond better to flunixin meglumine (Banamine) than to phenylbutazone (Bute). To him, this indicates that the pain is more a result of metabolic inflammation than being bony column related.

Trimming Protocol

Westman approaches Cushing’s laminitis cases as he would any other laminitic horse, though perhaps less optimistically.

“My system never changes,” he says. “My goal is always bony column alignment, so my trimming protocol is always the same.”

However, Westman notes that he will put these horses on a shorter schedule, “every 3 to 4 weeks if they are really bad since they tend to grow lots of heel.” He feels that this schedule helps “keep bone demineralization to a minimum, too.”

Like Bras, Westman is often forced to experiment to find the optimal shoeing configuration for these horses.

“I try to provide good caudal support,” he says. “I try to set the shoe around P3.”

Westman has found one newer product that seems to work well.

“I like the pour-in pads,” he says. “I start about 1/8 of an inch behind the apex of the frog and cover the whole back of the foot. That keeps the weight off the bone and changes the load in softer ground. I’ve been playing with different pour-in pads. You can almost pour the pad to act like a heart bar and play with different densities.”

Westman calls the process “trial and error. I’m playing with not only how well the material seems to hold up in different environments, but also how the foot seems to react. I listen to the client’s feedback on how the horse is doing.”

While he also adapts his shoeing strategies to the progress of the horse, Judd is emphatic on one point — X-rays are critical.

“You cannot treat a foundered horse without X-rays,” he says. “It’s just ridiculous to even try. If you don’t know where the bone is, you don’t know how to trim and trimming is key to the treatment of any foundered horse.

“You need to get lateral and AP radiographs at a minimum. You’re looking for rotation, sinking, sole depth and hoof-pastern axis. Without knowing them, you’re just wasting your time.”

Shoeing The Cushinoid Laminitic Horse

Once he gets radiographs, Judd says, “If the horse is incredibly sore initially, a lot of times we’ll put them on Styrofoam pads for a few days and on anti-inflammatories. If they are more stable, we’ve had good success putting wooden shoes on these horses.”

Judd believes the advantage of a wooden shoe “is that it supports the entire sole and you can be more aggressive with breakover with a wooden shoe than with any other kind of shoe I know of. (Laminitic horses) seem to be comfortable on wood. And you can trim out the surface of the shoe where the horse is more sensitive, distal to the apex of the frog.”

He notes that “a lot of these horses have thin soles. I think it’s because they probably have poor blood supply. You’ve got to try to get them to grow some sole.”

Judd acknowledges that there are many different approaches to shoeing laminitic horses.

“I think it’s accepted by most people that you need to wedge them at least a bit initially,” he says. “You need to take pressure off the deep digital flexor tendon and the coffin bone.”

Judd says he starts with a 3-degree wedge.

“You can do it with a regular shoe, with a pour-in pad to support the palmar half of the foot and a 3-degree wedge pad,” he says. “Or you can use a wooden shoe with a wedge pad.”

Like Westman and Bras, Judd assesses the success of his shoeing strategy by the comfort level of the horse.

“Depending on how well they respond,” he begins then starts again, he says. “You have to treat them based on how they’re doing. Typically, I leave them in a wooden shoe for two settings, then put on a 3-degree wedge with a pour-in pad with breakover. On every reset, I try to drop them by 1 degree until they’re finally in a flat shoe. In my mind that’s how it’s supposed to work. However, it doesn’t seem to work that way very often.”

There’s No Easy Way to Treat Cushing’s Disease