Perhaps you’ve noticed that your older horse is losing topline and isn’t shedding as well as she used to. Or maybe she’s drinking and urinating more frequently than normal. What’s going on?
Though you will definitely need to consult with your veterinarian, the answer may be Equine Cushing’s Disease.
What is Cushing’s Disease in Horses?
Cushing’s Disease, more technically known as Pituitary Pars Intermedia Dysfunction or PPID, is a neuro-degenerative disorder affecting aged horses (usually 15+). It’s caused by an enlargement of the pars intermedia of the pituitary gland which is housed in the brain. The pars intermedia is involved with the production of the stress hormone cortisol, as well as pain-relieving hormones known as endorphins. In horses with Cushing’s Disease, the pituitary gland produces hormones in excess, sending them into the bloodstream and affecting the horse’s entire body.
The pituitary gland, along with the hypothalamus, affects many regulatory functions in the body such as metabolism, immune response, body temperature, hunger/thirst, reproduction and growth, cardiovascular function, and stress response. All of these functions can be affected in a horse with Cushing’s Disease.
Horses with Cushing’s Disease also often have impaired gut health, which may lead to problems such as colic, diarrhea, and even pneumonia.
Though much is still unknown about Cushing’s Disease in horses, there are several factors that are thought to cause or at least be strongly associated with the disease. These include:
- Equine Metabolic Syndrome (EMS)
- Insulin Resistance (IR)
- Genetic factors
- Oxidative stress
- Chronic stress
- Toxins from the environment
What Are The First Signs of Cushing’s Disease in Horses?
Symptoms of Cushing’s Disease may be subtle at first. A horse may only show one or a few of the following symptoms:
- Hirsutism (failure to shed or delayed shedding)
- Other changes in hair coat such as patchy shedding, changes in coat color, shaggy hair on legs, face, or neck
- Decreased performance or lethargy
- Muscle loss along topline
- Weight loss with ‘pot-belly’ still existing
- Laminitis, often occurring in the fall
- Insulin Resistance
- Regional fat deposits (neck crest, tail head, above eyes, sheath/mammary area)
- Excessive sweating or anhidrosis (failure to sweat)
- Increased appetite/thirst
- Excessive urination
- Frequent infections
- Newly developed allergies/hypersensitivity to vaccinations, flies, etc.
It typically takes time for these symptoms to develop, but after the disease has progressed, a horse may show multiple symptoms. However, keep in mind that every horse is different in the symptoms they may show.
Diagnosing Cushing’s Disease
Diagnosing Cushing’s Disease is not always straightforward, especially if your horse is in the early stages. Some veterinarians may make a diagnosis based on hirsutism alone. However, diagnostic tests may include:
- ACTH Test: Often considered to be the most reliable indicator of Cushing’s Disease. This test measures the levels of adrenocorticotropic hormone. It can be performed any time throughout the year but must be adjusted to factor in seasonally high levels of ACTH during the fall.
- Dexamethasone Suppression Test: Measures cortisol levels both before and after administration of the steroid, dexamethasone. High cortisol levels after dexamethasone administration can indicate Cushing’s Disease. However, this test can be dangerous for some horses as it can trigger laminitis. If your horse has a history of laminitis or you believe he may be at risk for developing it, ask your vet about performing a different test. It’s also important to note that this test may not be reliable in the fall or early winter months.
- Domperidone Response Test: This is a newer test which uses domperidone, a dopamine-inhibiting drug (commonly used for decreased milk production and fescue toxicosis). Horses with Cushing’s Disease will quickly double their ACTH production after domperidone administration while normal horses will maintain normal ACTH levels. Many vets may not have access to this test yet, however.
Treating Cushing’s Disease
Some horses with Cushing’s Disease do not appear to show any adverse effects, so it’s possible that your veterinarian won’t prescribe medication. However, for horses in advanced stages of the disease or showing adverse symptoms, the treatment of choice is pergolide (Prascend). Your vet may recommend that your horse stay on the drug year-round or possibly just seasonally.
Other treatments your veterinarian may recommend include serotonin agonists, cortisol antagonists, and pain medications.
Feeding a Horse With Cushing’s Disease
Nutrition plays a very important role in treating Cushing’s Disease and can, in fact, help slow the progression of the disease. Because many horses with Cushing’s also have insulin resistance, feeding a low-sugar/starch diet is critical for their health. As far as forage goes, the following guidelines are recommended:
- Have your hay tested to know the sugar/starch content. WSC + starch levels should be less than 12% for Cushing’s horses.
- If your hay tests higher than 12% WSC + starch, or if you can’t get it tested, soak hay in water for 30-60 minutes before feeding to lower the sugar and starch content.
- Feed low-sugar and starch feedstuffs such as beet pulp, hay pellets, or a commercial feed specifically designed for horses with metabolic issues.
- Minimize or eliminate grazing on pasture during the spring and fall (when night-time temperatures fall below 40 degrees F). The safest time to graze is during the late night and early morning hours. Note: Some horses cannot tolerate any grazing during the spring/fall though, as it will trigger laminitis.
- For horses that can tolerate some grazing, use a grazing muzzle to restrict grass intake.
Digestive Support for Horses with Cushing’s Disease
Supplementing with a daily probiotic product such as EQ Probiotic Pellets/Extra Strength can also be beneficial for horses with Cushing’s Disease to help them better absorb critical nutrients. Probiotics also support a healthy immune system and can help prevent infections that Cushing’s horses may be prone to.
EQ Probiotic Pellets/Extra Strength provide the following:
- 50 Billion CFUs of Saccharomyces boulardii, a yeast strain of probiotic that supports a healthy immune system and is safe to use during antibiotic therapy
- L-Glutamine to help maintain a healthy intestinal tract, assist in fueling and repairing muscle tissue, and help prevent systemic infection
- Prebiotics to feed healthy gut microflora
If you suspect your older horse may have Cushing’s Disease, it’s important to speak to your veterinarian right away. Along with getting your horse on medication (if needed), diet and digestive support is key to managing this disease.