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Corro Stories

Signs of Cushing's Disease in Horses and Best Treatments

By Liv Gude Founder of Pro Equine Grooms

Horse lovers are likely familiar with Cushing's disease, the condition in which a horse's pituitary gland releases too many hormones. These hormonal changes start a chain reaction throughout the body, contributing to insulin problems, laminitis, and excessive hair growth.

Today, Cushing's in horses is called pituitary pars intermedia dysfunction (PPID) to clarify the source of the condition. In humans and dogs, Cushing's originates in the anterior portion of the pituitary gland. Turns out, horses want to do things their way, and the middle part - the intermediate portion - of their pituitary gland gets involved, hence the name change.

The origin is slightly different in horses than in other creatures, but the hormonal changes are similar.

 

What is the cascade of hormones in PPID?

As adrenocorticotropic hormone (ACTH) is released from the pituitary gland, it signals the adrenal glands to release cortisol - the stress hormone. Usually, higher cortisol levels trigger the brain to decrease ACTH, keeping cortisol levels in check. With PPID, there is no such mechanism, and the cortisol level increase unchecked.

This chain reaction affects many other things in the horse's body, from hair growth to insulin to the immune system. Some horses with PPID, but not all, develop insulin resistance, another metabolic disorder that increases the chance of laminitis.

What are the signs of PPID?

The signs of PPID are varied, and not all horses show the tell-tale extra hair and lack of shedding. Many horses are tested for PPID after laminitis, significant loss of topline, and an increase in fatty deposits. It is possible to find PPID before any signs appear, which is the best course of action, especially if you have an older horse. Some vets routinely test for PPID and insulin resistance when a horse is about 15 years old or more.

The primary signs of PPID are:

  • Excessive drinking and excessive urination
  • Lethargy and tiredness
  • Delayed shedding and an extra-long or curly hair coat
  • Wounds that take far too long to heal
  • Pockets of fat near the flanks, shoulders, tailhead, and mane crest
  • Weight loss and muscle loss, especially along the topline
  • Laminitis or tender hooves after a farrier visit
  • Strange sweating patterns
  • Loss of fitness
  • Hay belly appearance
  • Trouble fighting internal and external parasites

How is PPID detected in horses?

There is no conclusive test for PPID in horses, but there are diagnostic measures your vet can use for a more complete picture of your horse's metabolism. The dexamethasone (dex) suppression test is one way, as is measuring ACTH alone or in response to stimulation.

In the dex suppression test, your horse's cortisol levels are measured in the afternoon. Immediately following this, a dose of dexamethasone steroid is given, and cortisol levels are measured a day later.

The dexamethasone will reduce cortisol levels in healthy horses, but if a horse has PPID, the steroid will not change cortisol levels.

Cortisones, like dex, are tied to laminitis. Your vet may decide that this test is not beneficial to your horse. Additionally, testing with dex in the fall yields confusing results. A horse, even without PPID, will have actively rising ACTH levels in the fall. If the dex suppression test is used, the results may not be accurate.

There is another test, the thyrotropin-releasing hormone (TRH) stimulation test. Blood is drawn, TRH is administered, and 10 minutes later, another sample is collected. This test doesn't require a vet visit the next day and determines hormonal responses to the stimulant. For these reasons, the TRH stimulation test may be favored.

For horses that have a history of laminitis, it's worth exploring insulin and glucose levels as well, which may indicate insulin resistance. Your vet may also want to test for ACTH levels alone.

None of these tests are expensive or difficult and will alert you to possible risks long before your horse has trouble shedding or showing other signs. Early management of PPID can decrease the risk of laminitis and help your horse have a healthier lifestyle

Treatments of PPID for Horses

There is no magic treatment that will cure PPID, but there are many ways to keep your horse healthy. It boils down to medications, such as Prascend® and sometimes cyproheptadine, and lifestyle changes. The key is to minimize the risk of laminitis and help your horse's immune system fight off wounds and other diseases.

Your Horse's Diet

Even if your horse doesn't have insulin resistance, feed them as if they do. Low sugar and low starch forage come first. Limit the sugars and starches in their fortified feeds and grains. Look for hay and feeds that are below 10% in non-structural carbohydrate (NSC) values. Supplements are often loaded with added sugars for flavor, so find offerings without ingredients ending in "ose". Electrolytes and other supplements often have flavorful sugars, and there are low-sugar alternatives, as well.

Special Supplements

Science has come a long way when it comes to the equine diet. Many supplements help support the horse with metabolic issues, both PPID and insulin resistance. They work to balance the vitamins and minerals that influence insulin regulation.

Your Horse's Grazing

If you are lucky enough to have pasture for your horse, it's excellent for many reasons. Your horse can socialize, graze, reduce stress and ulcers, and move around. However, pasture can be high in sugars to the point of triggering laminitis in horses. Using grazing muzzles is the kindest way to have your horse wear a personal slow-feeder hay net and still enjoy grass time. The grazing muzzle works to limit both the quantity of grass and how fast it hits the hindgut, reducing the risk of laminitis.

Extra Grooming and Clipping

If your horse with PPID grows enough hair for the herd, bust out the clippers. If blanketing in the winter is not in the cards for your horse, clip with combs or guards to remove the bulk of the hair without compromising your horse's thermoregulation. As warm weather approaches, help your horse shed with grooming gloves and shedding blocks, and clip if needed. Many horses with PPID require clipping throughout the summer, so they don't overheat. Even if overheating isn't a danger, it's not comfortable wearing a sweater in warm weather.

Keep Exercising

The horse that moves will always be more comfortable. Counter any muscle loss and topline weakening with appropriate riding and lots of turnout.

Attend to Wounds and Practice Preventative Care

PPID causes a horse's immune system to run at a reduced level. Wounds take longer to heal, skin infections spread easily, and the ability to ward off parasites and sickness diminishes.

Your vet can help with any wounds or injuries that come up! Do fecal egg counts regularly to monitor your horse's parasite burden and treat according to your vet's protocols. The fecal egg count lets your vet know approximately how many ascarids your horse is hosting, and is a good indication of how his immune system can tolerate that load.

Partner with your vet to create a testing schedule for your horse's ACTH, insulin, and glucose levels. If your horse is on medications, follow-up blood work is usually needed to check if the dosage is suitable for your horse.

Many horses have long and illustrious careers with PPID. Making a few changes to your horse's management and some targeted vet care will help your horse stay happy and healthy.