Nowadays horses tend to live longer due to more attention being given to nutrition, hoof
and dental care and management of arthritis but with this we see certain medical conditions
occurring more frequently with the older population of horses. One such condition is
Pituitary Pars Intermedia Dysfunction (PPID) or commonly called Equine Cushing’s Disease
and is estimated to affect 21% of horses and ponies over the age of 15 but has been
documented in a horse as young as 7 years old. Ponies and quarter horses tend to be
overrepresented in affected breeds.
The pituitary gland, which is located just beneath the hypothalamus in the brain, controls
much of the hormone production in the body. PPID results from benign growth of a specific
region of the pituitary gland called the pars intermedia and the hypothalamus also
degenerates. The hypothalamus modulates body functions like thirst, hunger and
temperature regulation.
Many people are familiar with the typical signs associated with a Cushingoid horse such as a
long curly coat that fails to shed in summer, pot belly, muscle wasting, chronic laminitis and
increased thirst and urination but these are seen often in advanced cases. Early signs of the
disease can be more subtle and can be mistaken for the horse simply getting on in years.
Poor performance, subfertility, delayed wound healing, recurrent infections and soft tissue
injuries, a change in metabolism and weight loss, change in coat compared to other horses
kept on the farm. Ideally detection and treatment of PPID should occur before the advanced
signs are obvious as the horses quality of life may have been affected for several years
already.
Endocrinology is a complex branch of medicine that involves production and inhibition of
various hormones that have extremely powerful effects on the body. In the case of PPID,
growth of the pituitary gland disrupts many processes in the body and results in over
production of a variety of hormones, most importantly adrenocorticotrophic hormone
(ACTH) which regulates cortisol synthesis in the adrenal gland. This is also the main
hormone we test for in cases of suspected PPID. It is a simple blood test but may need to be
repeated if results are not definitive and is complicated by the fact ACTH levels are affected
by time of year. It is also worthwhile to test insulin levels as insulin dysregulation is often a
confounding factor especially in obese patients.
A drug called Pergolide is used to treat PPID. This mimics the effects of dopamine in the
body and through a series of hormonal interactions, inhibits the production of ACTH is the
pituitary gland and reduces cortisol levels in the body. Re testing of ACTH is recommended a few months after starting Pergolide in case dosage needs to be adjusted. Improvement of
clinical signs is often rapid when an adequate dosage is given. It should be noted that
treatment is not curative and merely improves clinical signs but if detected early,
Cushingoid horses can have a long and healthy life. Extra care should be given to teeth, feet,
worming, coat clipping and providing adequate water for these horses.
If you have any concerns about your horse, please don't hesitate to get in touch with one of our Vets by calling our office on 03 5975 6586 or emailing contact@racetrackvetservices.com
