PPID, or pituitary pars intermedia dysfunction, is a hormonal disorder in horses caused by progressive changes in a specific region of the pituitary gland at the base of the brain. You may also hear it called equine Cushing’s disease. It primarily affects older horses and leads to a range of problems, from a coat that won’t shed properly to painful hoof conditions like laminitis. PPID is manageable with medication and dietary changes, but it’s a progressive condition that requires lifelong monitoring.
How PPID Develops
The pituitary gland in a healthy horse has a section called the pars intermedia that’s kept in check by dopamine, a chemical messenger sent from the brain. Dopamine acts like a brake, preventing the pars intermedia from overproducing hormones. In horses with PPID, the nerve cells that supply dopamine gradually deteriorate. Without that brake, the pars intermedia grows and produces excess hormones, including ACTH (a stress-related hormone that influences cortisol levels, metabolism, and immune function).
This hormonal overproduction is what drives the wide range of symptoms seen in PPID. It can disrupt how the body handles sugar, weaken the immune system, and alter how the horse stores fat and maintains muscle. The degeneration is slow and progressive, which is why early signs are subtle and often mistaken for normal aging.
Early Signs vs. Advanced Symptoms
One of the trickiest aspects of PPID is that its early signs look a lot like a horse simply getting older. The most common first clue is delayed shedding: a horse that hangs onto its winter coat well into spring or summer, or develops patches of longer hair. At this stage, owners may also notice mild changes in energy level, subtle shifts in body condition, or a slightly pot-bellied appearance that wasn’t there before.
As the disease progresses, symptoms become harder to miss. The hallmark sign is hypertrichosis, an abnormally long, curly coat that fails to shed normally. This is the one symptom considered definitive for PPID. More advanced cases can include:
- Muscle wasting, especially along the topline, giving the horse a swayback appearance
- A pendulous abdomen from weakened abdominal muscles
- Abnormal fat deposits, often above the eyes or along the crest of the neck
- Excessive sweating
- Increased drinking and urination, which typically appears in more severe cases
- Recurrent infections, including skin conditions, hoof abscesses, or respiratory issues, due to a suppressed immune system
- Laminitis, a painful inflammatory condition of the hooves
- Behavioral changes and lethargy
The Laminitis Connection
Laminitis is one of the most serious complications of PPID and often the reason the condition gets diagnosed in the first place. The link runs through insulin dysregulation. Many horses with PPID develop abnormally high insulin levels, and prolonged high insulin is strongly associated with laminitis. This type, sometimes called endocrinopathic or insulin-associated laminitis, can be painful enough to be debilitating. In severe cases it can lead to euthanasia.
Not every horse with PPID will develop laminitis, but the risk is significant enough that managing insulin levels becomes a central part of treatment. If your horse has had unexplained bouts of laminitis, especially later in life, PPID should be on the list of possible causes.
How PPID Is Diagnosed
The most common diagnostic approach involves measuring ACTH levels in the blood. A horse with PPID typically has elevated baseline ACTH because the pars intermedia is overproducing it. However, there’s an important catch: ACTH levels naturally rise in healthy horses during autumn. A blood draw in September might show elevated ACTH that would be perfectly normal for the season. One study of healthy horses in Canada found average ACTH levels of about 21 pg/mL in spring compared to 31 pg/mL in fall. Veterinarians use seasonally adjusted reference ranges to account for this, and geography can influence normal values too.
For horses with borderline or unclear results, a TRH stimulation test provides more information. This involves drawing a baseline blood sample, injecting a small amount of a hormone called TRH (thyrotropin-releasing hormone), then drawing another sample 10 minutes later. In a horse with PPID, the abnormal pituitary cells overreact to this stimulation, producing a spike in ACTH that’s larger than what a healthy horse would show. This test is especially useful for catching early-stage PPID when resting ACTH levels may still fall within the normal range.
Treatment With Pergolide
The primary treatment for PPID is a daily oral medication called pergolide. It works by mimicking dopamine, essentially replacing the chemical brake that the horse’s body can no longer provide on its own. Pergolide doesn’t cure PPID or stop the pituitary from degenerating, but it reduces the excess hormone production that drives symptoms.
Treatment starts at a low dose and is adjusted based on follow-up bloodwork and clinical response. In one controlled study, four weeks of pergolide was enough to significantly reduce ACTH levels in horses with PPID, confirming the drug was working at a biochemical level. But visible improvements in coat quality, muscle mass, and body condition take longer, often several months. Owners should expect a gradual process rather than a quick turnaround.
Because PPID is progressive, the dose often needs to be increased over time. Periodic blood testing helps your veterinarian determine whether the current dose is still controlling hormone levels adequately. Some horses do well on a stable dose for years; others need adjustments more frequently.
Diet and Daily Management
Dietary management is critical for horses with PPID, particularly those with insulin dysregulation. The goal is to minimize sugar and starch intake to help keep insulin levels stable and reduce laminitis risk.
Feeds with more than 20% non-structural carbohydrates (NSC) or more than 3% molasses should be avoided in horses showing signs of insulin problems. This rules out many sweet feeds and, perhaps surprisingly, some senior feeds that are marketed toward older horses but contain high levels of molasses and starch. A better option is a pelleted feed that’s higher in fiber (above 10%) and fat (above 5%), which provides calories without the sugar spike. Concentrates should only be fed as needed to maintain a moderate body condition, and splitting them into small, frequent meals produces less disruption to blood sugar and insulin.
Beyond diet, general management matters too. Regular hoof care is essential given the laminitis risk. Dental care helps older horses get the most nutrition from their feed. A consistent deworming program and prompt attention to wounds or infections are important because PPID horses have weakened immune defenses. Routine vaccinations may also warrant extra attention for the same reason.
Living With PPID
PPID is not a death sentence. Many horses live comfortably for years after diagnosis with proper medication, dietary management, and attentive care. The condition does progress over time, and the medication dose will likely need to be adjusted as the horse ages, but the goal of treatment is to maintain quality of life rather than to achieve a cure.
The biggest factor in long-term outcomes is catching it early. A horse whose PPID is identified at the delayed-shedding stage and started on treatment before laminitis or serious muscle loss develops has a much better outlook than one diagnosed only after a severe laminitis episode. If you have an aging horse, paying attention to coat changes, energy levels, and body condition shifts can make a meaningful difference in how well the disease is managed going forward.