Early Clinical Signs of PPID in Horses

When knowledgeable horse owners see an aged horse with a shaggy coat and sore feet, they immediately think of pituitary pars intermedia dysfunction, also known as PPID or equine Cushing’s disease. Owners may then call their veterinarians to discuss these clinical signs and consider testing their horses for PPID.

Haircoat abnormalities and laminitis, however, are believed to occur late in the course of disease. As a result, a group of European veterinary researchers considered what other clinical signs may suggest PPID, and if PPID could be diagnosed earlier in the course of disease before coat changes and laminitis develop.^*

In addition to haircoat abnormalities (delayed shedding, unusually long or shaggy coat, atypical guard hairs) and laminitis, several clinical signs are potentially attributable to PPID:

• Weight loss, loss of condition, or muscle atrophy
• Regional adiposity, including prominent fat pads above the eyes (supraorbital fat pads)
• Poor performance
• Lethargy
• Increased appetite
• Excessive drinking and urinating
• Suspensory ligament laxity
• Behavior changes

One way of testing horses for PPID involves measuring levels of the adrenocorticotropin hormone (ACTH) in a single blood sample. If ACTH is high, then the horse likely has PPID. To determine if an association between certain clinical signs and ACTH levels exist, the research team collected data from owners and veterinarians of 280 horses ranging in age from 11 to 35 years (average of 21 years).

One hundred eighteen (42%) of the horses had “high” ACTH levels, 131 had equivocal ACTH levels, and 31 horses had low ACTH levels.

“Not surprisingly, horses with delayed shedding and laminitis had significantly higher ACTH levels than horses without these clinical signs,” explained Kathleen Crandell, Ph.D., a nutritionist for Kentucky Equine Research.

Clinical signs were then divided into one of three “dimensions” for further analysis. Dimension one included regional adiposity, supraorbital fats pads, history of laminitis, chronic laminitis, and increased appetite. These clinical signs occur commonly in horses with metabolic syndrome. Dimension two included clinical signs suggestive of early PPID, including poor performance, weight loss, muscle atrophy, lethargy, and acute laminitis. Finally, dimension three included clinical signs typically attributable to advanced PPID: muscle atrophy, delayed shedding, weight loss, and hypertrichosis (excessive hair growth).

“Dimensions one and three were both predictors of high ACTH levels but not dimension two. This means that a high ACTH level is not a sensitive marker for diagnosing PPID, especially in the early stages of disease,” explained Crandell.

Why the clinical signs of dimension one, representing equine metabolic syndrome, were also associated with high ACTH levels like dimension three (advanced PPID) is unknown.

These data, according to the researchers, emphasize the importance of focusing on finding biomarkers that can detect PPID at an earlier stage of disease.

Owners are encouraged to have their horse examined by a veterinarian once they begin seeing signs of hair coat changes, laminitis, weight loss, and muscle atrophy. Even if it may seem early in the course of disease, ACTH may still be sufficiently elevated that a diagnosis of PPID can be made. Alternatively, in the face of equivocal test results, we would know to monitor those horses carefully. In addition, it may be prudent to test these horses for metabolic syndrome as well.

Once diagnosed, veterinarians often prescribe pergolide. But the horse’s nutrition must also be addressed.

According to Crandell, “Diligent attention to the feeding program for the PPID horse is crucial for keeping the horse healthy. Feeding a diet low in nonstructural carbohydrates (NSC) is often important for PPID horses, particularly when insulin dysregulation is present, as these horses can be susceptible to laminitis. Dental issues can also be present in older PPID horses, so feeding soaked chopped, cubed, or pelleted forages will help to meet fiber requirement and limit NSC.”

Crandell also recommends offering a low-starch ration balancer that supplies the essential amino acids when there are signs of muscle atrophy or loss of topline, as well as natural-source vitamin E, chelated trace minerals, B vitamins, biotin, yeast culture, and organic selenium.

^*Fouché, N., C. Doras, G. Schüpbach-Regula, A. Scherer, B. Freudenschuss, and V. Gerber. 2025. Association between adrenocorticotropic hormone concentration and clinical signs of pituitary pars intermedia dysfunction in Swiss and Austrian equids. Journal of Veterinary Internal Medicine 39(2):e70008.