Cushing’s Disease In Horses

Cushing’s disease in horses has become nearly as common of a household name as laminitis and colic in the last several years. Cushing’s is a disorder commonly found in middle-aged to older horses. The disease is often diagnosed in horses between 17 and 23 years of age. Though a simple disease in origin, it often manifests as a host of many symptoms, affecting vital functions throughout the horse’s body.

What Is Cushing’s Disease In Horses?

What Is Cushing’s Disease In Horses

All horses contain a vital organ called the pituitary gland, a prune-sized structure that is also known as the “master gland”. Cushing’s disease is also known as PPID, or Pituitary Pars Intermedia Dysfunction, due to the misbehavior of this gland. The pituitary gland resides in the base of the brain, and is responsible for releasing directive hormones that indicate to other structures in the body when to release other hormones to coordinate circulation, kidney function, metabolism, growth, and reproduction.

Cushing’s disease in horses is a malfunction of the pituitary gland, in which the gland releases too much adrenocorticotropin hormone, or ACTH. This hormone triggers the release of cortisol and other hormones, which leads to various health issues throughout the horse’s body. Over time, Cushing’s disease can also develop into small tumors around the pituitary gland.

The reason that the pituitary gland malfunctions really has no other basis than old age. The gland is controlled by a handful of nerves. Some horses’ nerves degenerate at a faster rate than others, causing the onset of this disease and its many subsequent symptoms.

Warning Signs & Common Symptoms Of Cushing’s Disease

Warning Signs & Common Symptoms Of Cushing’s Disease

Because the excess of ACTH in the body results in higher levels of cortisol and other hormones, a horse’s body will respond with a variety of symptoms, including:

  • Muscle wasting, where the topline and other muscular areas begin to degenerate
  • Rounded abdomen (or “potbelly”) and fat deposits, particularly along the crest of the neck and the dock (base of the tail)
  • Growth of long, curly hair
  • Delayed shedding in the Spring/Summer
  • Overall lethargy and decrease in energy
  • Laminitis
  • Proneness to infection
  • Infertility
  • Increased drinking and urination
  • Neurological issues/blindness
  • Abnormal sweating

The most notable of these symptoms are the delayed shedding and the changes in the horse’s conformation. The difference in their physique can be drastic, as their muscle density and conformation gives way to abnormal fat storage.

Should you see any or multiple symptoms on this list, the best thing to do is to reach out to your veterinarian to complete an exam and diagnostic tests.

Diagnosis & Ruling Out Equine Metabolic Syndrome

Diagnosis & Ruling Out Equine Metabolic Syndrome

Thankfully, in the last decade or so, understanding about PPID in horses has become much more common. Veterinarians can sometimes use multiple symptoms characteristic of Cushing’s disease to make a positive diagnosis. However, some of the same symptoms – obesity, chronic laminitis, and insulin resistance – could also be a sign of a different illness altogether: Equine Metabolic Syndrome.

Unlike Cushing’s disease, Equine Metabolic Syndrome does not come with certain symptoms, like the long, curly hair. Insulin resistance is the culprit of Equine Metabolic Syndrome, not the pituitary gland.

In order to correctly diagnose Cushing’s disease in horses, veterinarians can administer one of two tests that assess the pituitary gland.

  1. The first is the dexamethasone suppression test, where the veterinarian has to come out twice over a 24-hour period. The vet will take the first blood sample in the afternoon, followed by an injection of a low dose of dexamethasone into the horse’s muscles. The vet will return around noon the next day to collect another blood sample. After that, both blood samples are compared for cortisol levels. An unaffected horse’s body will react to the dexamethasone by suppressing cortisol production, whereas a horse with Cushing’s disease will have little-to-no change in its cortisol levels. Though deemed incredibly effective in diagnosing Cushing’s, this test could increase the risk of laminitis in horses that are already prone to it. Because of this, many veterinarians will favor another test, which measures ACTH in the blood plasma.
  2. The ACTH measurement test is much less invasive, requiring only one blood sample. The sample is then tested for levels of ACTH in the bloodstream. A horse with Cushing’s will have much higher levels of ACTH than normal horses. The drawback of this test is that ACTH levels can decrease in the sample kit if not handled properly. Alternatively, horses under stress and pain from other conditions can also result in high ACTH. Sometimes a veterinarian will couple the ACTH measurement with tests that check the horse’s insulin resistance and hyperglycemia, which are other earmarks of the disease.

Treatment Of Cushing’s Disease

Treatment Of Cushing’s Disease

Because understanding of the disease has increased in the past several years, early diagnosis is much more common than it ever has been. While PPID cannot be reversed or cured, the symptoms can be managed so that the horse can live with a greater quality of life.

The primary medical treatment option is an FDA-approved medication called Prascend, whose active ingredient is pergolide. Pergolide was originally developed for humans suffering from Parkinson’s disease. Enough commonalities have been found between human Parkinson’s and equine Cushing’s to treat them similarly, though the diseases are still notably different.

Living With Cushing’s Disease

Living With Cushing’s Disease

Because Cushing’s disease affects the horse’s insulin and blood sugar levels, avoiding sugars and starches in their diet will help their overall health in the long run. Focus on low-sugar, high-fiber feed, and avoid treats, sweet feed, and pasture grazing as much as possible.

Remember, too, that horses living with Cushing’s disease will also have weak immune systems and will be prone to infections. Preventative health, including regular vet checks, deworming, dental checks, and quality hoof care is a must to ensure that they maintain the best possible quality of life.

All thanks to the latest research and equine medical practice, early diagnosis of Equine Cushing’s is more possible than ever. As a result, symptom management and treatment can allow affected horses to live healthier and longer lives than ever before.

References:

  1. https://www.smartpakequine.com/content/cushings-disease-horse
  2. https://aaep.org/horsehealth/equine-endocrinology-cushings-disease-and-metabolic-syndrome
  3. https://equusmagazine.com/diseases/managing_cushings_disease_042709
  4. https://aaep.org/horsehealth/equine-cushings-disease-equine-pituitary-pars-intermedia-dysfunction
  5. https://www.petmd.com/horse/conditions/endocrine/c_hr_cushings_syndrome
  6. https://equusmagazine.com/management/endocrinesystem_062907-8306
  7. https://thehorse.com/118494/what-causes-equine-cushings-disease/
Lindsey Rains
Lindsey Rains is an equestrian blogger and creator of Alta Mira Horsemanship. She focuses on communication between horse and rider and kind training tactics. She resides in Liberty Lake, WA, USA, with her husband. Visit her blog. You can also follow her on Pinterest, Facebook, Instagram, Twitter, or YouTube.


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