Understanding Equine Cushing's Disease (Pars Pituitary Intermedia Dysfunction): Causes, Diagnosis, and Management

As horses age, they can become at an increased risk of pars pituitary intermedia dysfunction (PPID - formerly known as Equine Cushing’s). PPID is an endocrine disease that can result in various, subtle clinical signs such as an abnormal hair coat, loss of muscling, or even increased drinking. PPID affects more than 1 in 5 senior horses, and can sneak up slowly and cause significant health challenges over time, including the risk of life-altering laminitis.

I’ve seen the effects of PPID firsthand in practice, and I know how confusing the early signs can be. Let’s explore what this disease is, what it does to your horse’s body, and what you can do to manage it effectively.

What is PPID in Horses?

Pituitary Pars Intermedia Dysfunction (PPID), is a hormone-related condition that affects the pituitary gland of horses. This small, but important gland is located at the base of a horse's brain and helps control many essential body functions by sending signals that regulate things like metabolism, stress response, and water balance.

In horses with PPID, a specific part of the pituitary gland called the pars intermedia becomes overactive. Over time, it can enlarge and produce too many hormones, especially one called ACTH (adrenocorticotropic hormone). The enlargement of the gland can affect surrounding tissue and negatively impact reproductive function and/or drinking habits.  In addition, the increase in the ACTH hormone can act on the adrenal glands to increase the release of other hormones, such as cortisol, which will subsequently have negative effects on multiple body systems, like the immune system. 

It is very important to understand that the only risk factor for PPID is advancing age.  That is why PPID is very uncommon in young horses. Unfortunately, there is no known way to prevent PPID but there is a treatment available. 

While PPID  itself isn’t painful or life-threatening, the side effects can greatly impact your horse’s comfort, health, and quality of life, especially if left undiagnosed or untreated.

Fun facts - when PPID was first recognized in horses, it was termed Equine Cushing’s because it shared some of the characteristics to human and canine Cushing’s.  However, with time, we began to recognize that there were many differences in the pathology in horses as compared to other species.  Therefore, the name pars pituitary intermedia dysfunction was coined to better represent the disease process. 

Clinical Signs of PPID

One of the challenges with PPID is that the symptoms can vary widely and in the early stages, they’re often subtle or mistaken for normal aging. However, recognizing the clinical signs early can make a big difference in your horse’s long-term comfort and quality of life.

  • Hirsutism: A long, curly hair coat that doesn’t shed normally, often the most recognizable symptom.
  • Laminitis: Inflammation of the laminae in the hoof, leading to lameness.
  • Muscle Wasting: Noticeable loss of muscle mass, especially along the topline and hindquarters.
  • Lethargy: Reduced energy levels, a quiet demeanor, or an overall sluggishness.
  • Abnormal sweating (hyperhidrosis): Either excessive sweating or a coat that stays unusually dry.
  • Increased thirst and urination: Known as polydipsia and polyuria, often one of the earliest subtle changes observed.

Horses in advanced stages of PPID may develop a characteristic “teddy bear” appearance, with a thick, curly coat and loss of topline muscle. But in horses with mild or early PPID, these signs can be easy to overlook. In some cases, laminitis is already developing quietly in the background before more obvious signs emerge.

That’s why early screening is so important, especially for horses entering their mid to late teens. In the next section, we’ll explore how PPID is diagnosed and the challenges that can come with catching it in its early stages.

Diagnosing PPID

Diagnosing PPID involves a combination of recognizing clinical signs and running specific blood tests to evaluate hormone levels. The primary hormone measured is adrenocorticotropic hormone (ACTH), which tends to be elevated in horses with PPID, especially in more progressed cases.

  1. Baseline ACTH Test: A simple blood draw to measure the horse’s resting ACTH levels. This test is effective for horses showing clear clinical signs and can be performed year-round. However, ACTH levels naturally rise in the fall, so labs may adjust reference ranges to account for seasonal changes.
  2. TRH Stimulation Test: This test provides a deeper look at how the pituitary gland responds to stimulation. A baseline blood sample is collected, thyrotropin-releasing hormone (TRH) is administered, and then a second sample is taken 10 minutes later. Horses with PPID typically show a dramatic spike in ACTH levels following TRH. Note: this test is not recommended during the fall, when natural hormonal fluctuations can interfere with results.

It's important that horses are calm and not stressed during testing, as stress can temporarily raise ACTH levels and lead to misleading results.

In early or mild cases of PPID, hormone levels may still fall within the normal range. For these horses, dynamic tests like the TRH stimulation test or the overnight dexamethasone suppression test may be necessary to uncover abnormal hormone patterns. However, because even these tests have limitations, your veterinarian may recommend beginning treatment based on clinical signs alone, especially when symptoms are clearly pointing to PPID.

Because some horses with PPID also have insulin dysregulation (ID), it is recommended to include insulin testing as part of the diagnostic process. Horses who are affected by ID are at an increased risk for laminitis, which can significantly affect quality of life. Please be aware that some PPID horses with ID can also be affected by equine metabolic syndrome (EMS). It is important to consult with your veterinarian about your test results to ensure you are appropriately treating and managing your horse who is affected by endocrine disease.   

A full geriatric wellness panel, including blood chemistry, can also help assess overall health and rule out other conditions that may affect older horses.

Treatment Options for PPID

While there is no cure for PPID, the good news is that it can be managed successfully with the right treatment and care. The goal of treatment is to reduce hormone imbalances, control clinical signs, and help your horse maintain a good quality of life for as long as possible.

The mainstay of treatment is a medication called pergolide, available as an FDA product called Prascend?. This drug is a dopamine agonist, meaning it helps restore proper signaling in the brain to reduce the overproduction of hormones from the pituitary gland. This medication is a small tablet, given orally once a day, typically for life. While compounded pergolide is sometimes available, it is not recommended due to inconsistent quality, safety, and effectiveness.

Ongoing research is exploring other medications, such as cabergoline, which is given as an intramuscular injection every 7–10 days. Cabergoline acts in a similar manner to pergolide. At this time, Prascend? remains the gold standard due to its proven results and FDA approved status.

Lifestyle and Management Strategies for Horses with PPID

Managing PPID isn’t just about medication, it also involves daily care and support to keep your horse feeling their best. With consistent attention to nutrition, routine veterinary care, and environmental management, many horses with PPID can continue to lead active and comfortable lives.

Nutrition and Weight Management

Support weight gain in underweight horses:

  • Offer easily digestible fiber, such as pelleted senior feeds that are easier to chew and digest, especially for horses with worn or missing teeth.
  • Add fat supplements, such as oils, if extra calories are needed.

Control sugar intake in horses with insulin dysregulation:

  • Eliminate or reduce grain-based feeds.
  • Limit pasture access, especially during the spring and fall when grass sugar content is highest.
  • Test your hay to ensure the starch content isn’t too high. 

Address obesity in easy keepers:

  • Reduce calorie intake with a controlled diet.
  • Increase regular, safe exercise to support weight loss and improve insulin sensitivity.

Dental and Routine Veterinary Care

  • Schedule routine dental exams to address issues affecting eating and digestion.
  • Maintain a consistent parasite control and vaccination program to protect overall health.
  • Include regular bloodwork and metabolic testing as part of geriatric wellness checks to monitor for complications or progression.

Laminitis and Hoof Care

  • Horses with PPID and ID are at increased risk of laminitis, even with subtle or undetectable early signs.
  • Work with a skilled farrier for therapeutic trimming and shoeing, especially if signs of laminitis are present.
  • Use pain management or anti-inflammatory medications as prescribed to support comfort in horses with chronic hoof issues.

Seasonal Grooming and Comfort

  • If your horse doesn’t shed normally, body clipping during warm months can help regulate body temperature and improve comfort.
  • Monitor for abnormal sweating patterns (too much or too little) and adjust turnout or blanketing as needed.

Supporting Your Horse Through PPID

While a PPID diagnosis can feel overwhelming at first, it doesn’t have to be the end of your horse’s active, comfortable life. The key is staying proactive and working closely with your veterinarian, monitoring for subtle changes, and adjusting your horse’s care as their needs change.

If you suspect your horse may be showing signs of PPID or if they’re entering their golden years, don’t wait to schedule a wellness exam. A few simple steps now can make all the difference in keeping your horse comfortable, healthy, and by your side for many more seasons to come.