Pituitary pars intermedia dysfunction (PPID), commonly called Cushing’s disease, usually develops in older horses. Its early signs can be subtle, so owners may initially mistake them for ordinary aging, seasonal coat changes, or a gradual loss of fitness.
Early recognition matters because PPID can affect immune function, muscle condition, comfort, and laminitis risk. A veterinarian can evaluate the complete pattern and recommend appropriate testing.
Common Signs of PPID in Horses
- Coat changes: A longer, thicker, or curly coat, delayed shedding, or failure to shed normally is one of the most recognizable signs.
- Increased thirst and urination: Some affected horses drink more water and urinate more frequently.
- Loss of muscle: Muscle loss may be especially noticeable along the topline or hindquarters, sometimes with a pot-bellied appearance.
- Changes in fat distribution: Fat may accumulate above the eyes, along the crest, around the tailhead, or in other unusual areas.
- Lethargy or reduced performance: The horse may seem less energetic, weaker, or less interested in exercise.
- Increased sweating: Some horses sweat more than expected, particularly when carrying an abnormally long coat.
- Recurring infections: Hoof abscesses, dental disease, sinus infections, and skin infections may occur more frequently.
- Laminitis: Horses with PPID may also have insulin dysregulation, which can substantially increase laminitis risk.
What Causes PPID?
PPID is a disorder of the pituitary pars intermedia. Changes in the hormonal control of this part of the pituitary allow it to become overactive and produce abnormal amounts of certain hormones, particularly ACTH and related peptides.
It is not accurate to describe equine PPID simply as adrenal overproduction of cortisol. Blood cortisol concentrations often remain within the normal range, and cortisol testing alone is not the standard way to diagnose the condition.
How Veterinarians Diagnose and Treat PPID
A veterinarian will consider the horse’s age, clinical signs, medical history, and endocrine test results. Testing commonly involves measuring blood ACTH. A thyrotropin-releasing hormone (TRH) stimulation test may be recommended when early PPID is suspected or resting ACTH results are unclear.
Pergolide is the established medication for controlling PPID in horses. Treatment usually requires ongoing veterinary monitoring because the dose may need adjustment based on clinical response and follow-up testing. Good dental care, farrier care, parasite control, body clipping when needed, and management of infections are also important.
If a horse with suspected PPID becomes footsore, reluctant to turn, unusually warm in the hooves, or develops stronger digital pulses, contact a veterinarian immediately. Laminitis is a medical emergency.
Where Magnesium Fits
Magnesium is an essential part of a balanced equine diet, but magnesium supplementation does not diagnose, cure, or directly treat PPID. Current evidence does not establish PPID or pergolide treatment as a cause of magnesium deficiency.
Nutrition still matters. Older horses may have changing calorie, protein, dental, metabolic, or mineral needs, and horses with insulin dysregulation often require careful dietary management. A veterinarian or qualified equine nutritionist can review the complete ration and determine whether additional magnesium is appropriate for the individual horse.
When additional magnesium is appropriate, MagRestore® can be considered as part of the horse’s broader feeding program. It should not replace endocrine testing, pergolide, veterinary treatment, or management of insulin dysregulation.
For additional veterinary information, see the Merck Veterinary Manual overview of PPID in horses. For help reviewing your horse’s feeding program, you can also schedule a consultation with Performance Equine Nutrition.