July 13, 2023 — Equine pituitary pars intermedia dysfunction is a well-known disease in horses and is thought to be the most common endocrine (gland) disorder affecting equids. Research estimates upwards of 15-30% of horses over the age of 15 have PPID, and some experts believe the number might be even higher.
For many of us old enough to remember, equine Cushing’s disease, as it was known, was an oddity at the time. However, improved diagnostic tests, coupled with a better grasp on pituitary physiology, suggest the disease is more common than originally thought.
Abnormal Hormone Production Causes Clinical Signs of Disease
As the name suggests, PPID is a disease of the pituitary gland, a small organ located in the brain. The pituitary gland produces and stores hormones crucial to many different bodily functions, including metabolism, reproduction and growth. One of the hormones produced by the pituitary gland is adrenocorticotropic hormone. In PPID, the pituitary gland becomes diseased and begins to produce too much ACTH. This hormone has many functions, including increasing production of cortisol, which in excess, is what leads to disease symptoms many horse owners know:
- Hair coat changes
- Lethargy
- Behavior changes
- Muscle loss
- Pot belly
- Recurrent infections
- Laminitis
Diagnosis
PPID can be diagnosed through specialized blood tests in combination with clinical signs. Many of the tests can be performed in the field and don’t require referral to a specialty clinic, although a referral is sometimes needed for some extremely specific tests.
Blood tests that might be recommended include:
- Measurement of ACTH
- TRH stimulation test
- Dexamethasone suppression test
- Measurement of blood insulin level
It's important to know that each test has pros and cons, and none are 100% accurate all the time. Your veterinarian will recommend the test – or combination of tests – that is best for your horse.
Treatment
It's important for horse owners to know that although PPID is treatable, it isn't curable, and therapy is lifelong.
Successful treatment typically relies on a combination of medication, diet change and exercise. As always, staying on top of wellness care such as routine dental examinations, parasite control, farrier work and vaccinations is important.
Finding better ways to diagnose and treat PPID
Because of PPID’s significant impact on horse and pony health and well-being, Morris Animal Foundation focused its latest call for proposals on equid health.
“PPID is an important disease to study because it’s so common,” said Dr. Nicola Menzies-Gow, Professor in Equine Medicine at the Royal Veterinary College in the United Kingdom. “PPID causes clinical signs which can have a significant impact on the affected animal’s quality of life.”
Although the equine medical community has recognized PPID for decades, many unanswered questions remain. This is where the Foundation stepped in and reached out to veterinary scientists to submit projects aimed at tackling PPID.
“There are still a lot of big questions about PPID that need answers,” Menzies-Gow said. “For example, we don’t know what actually causes PPID. We also need a diagnostic test that can detect the disease with 100% accuracy in all animals, and we need more information about how our current treatment affects the risk of laminitis.”
Menzies-Gow is one of the equine medicine experts who recently reviewed project proposals submitted to Morris Animal Foundation. Each proposal is carefully scrutinized and only the absolute best projects are recommended for funding.
Several excellent PPID-focused proposals from researchers around the world were reviewed. Projects recommended for funding include a unique study that hopes to harness the power of artificial intelligence in the early diagnosis of PPID. Another study will revisit the use of an older drug, cyproheptadine, in the treatment of PPID.
It’s clear that PPID has risen from oddity to an important disease in equids, and that it has a larger impact on health and welfare than previously suspected. Morris Animal Foundation is excited to help improve the quality of life of horses and ponies through our new grants!
Learn more about the Foundation’s work to help horses and how you can support researchers around the worldworking on improving diagnostics and treatments for our equid friends.