By NEC Veterinary Intern, Dr. Antonella Pannunzio.
Equine Cushing’s Disease, also known as Pituitary Pars Intermedia Dysfunction (PPID) is the most common endocrine disorder diagnosed in horses.
Cushing’s disease is a progressive disorder caused by a benign tumor affecting a part of the brain known as the pituitary gland.
Normally, the pituitary gland releases hormones that help regulate normal body functions. PPID occurs when there is an abnormal growth of the pars intermedia portion of the pituitary gland, which results in chronically increased cortisol (stress hormone) levels that negatively affect the body in a number of ways including but not limited to muscle wasting, body temperature dysregulation, weakened immune system, insulin resistance.
While previously associated with older horses, it has been reported in horses as young as 7 years old. All breeds of horses can be affected but ponies and Morgan horses appear to be predisposed.
Cushing’s disease is a progressive disorder. The symptoms may be slow to present but will ultimately progress with time.
Clinical signs include, but are not limited to:
- Excessively long hair coat which often fails to shed out at normal seasonal intervals.
- Excessive water intake and urination
- Weight loss
- Laminitis or multiple laminitis episodes
- Fat deposits on the neck, over the eyes, above the tail, sheath
- Pot-belly due to lack of tone in the abdominal musculature
- Increased sweating
- Lethargy or poor performance
- Recurrent infections, such as sole abscess or skin infections
- Reproductive disorders such as abnormal estrous cycles in a mare
In cases of suspected PPID, there are two main diagnostics tests that can be performed by your veterinarian, resting ACTH concentration, and a thyrotropin-releasing hormone (TRH) stimulation test.
To initially screen, your veterinarian can collect a single blood sample to test for resting ACTH concentration, which may be enough to make a diagnosis in the later stages of PPID, or in horses with numerous symptoms.
The other test that can be performed is the Thyrotropin-releasing hormone (TRH) stimulation test to confirm diagnosis in a horse with minimal symptoms. This test involves obtaining a blood sample, administering thyrotropin-releasing hormone (TRH) intravenously, and collecting a second blood sample 10 minutes later. If ACTH levels in the blood sample increase excessively in response to TRH, the test is considered positive for PPID. Unfortunately, TRH is very difficult to obtain in Australia, please consult with your vet to discuss further.
Treatment is quite simple, and consists of an oral daily medication called Pergolide (PrascendⓇ). The dose may vary depending on the individual horse’s response, and ACTH concentration should be rechecked after initiating treatment to determine response. Owner has to be aware that changes in symptoms may not be noticed until 2 months after treatment is started.
It is important to note that treatment can improve clinical signs and quality of life of horses diagnosed with PPID but the condition can only be managed and not cured.
Early diagnosis can offer better quality of life and treatment is generally successful at keeping your horse comfortable as long as it is continued for the remainder of the horse’s life.
Management and Nutrition of horses with PPID
In addition to medical treatment, it is suggested routine wellness care including farrier care, deworming, vaccinations and dental care. Due to the lack of being able to control their own body temperature, it is important to provide shelter or rugs in the cooler months of the year. Nutritional management is also very important, and it is recommended a good quality diet low in starches and sugars. Horses should have grass intake restrictions especially during the day (as sugar are likely to be at their highest level)
If you think your horse has symptoms consistent with Cushing’s disease, you should contact your veterinarian to discuss diagnostics and treatment.
If you are worried that your horse may be affected by Cushings Disease give us a call at the clinic and we can discuss the blood tests that are required for diagnosis. Contact the clinic on (02) 49276135 or firstname.lastname@example.org. More information on PPID and laminitis can be found at http://www.talkaboutlaminitis.com.au
- Equine Internal Medicine. Reed. Third edition
- Current Therapy in Equine Med Robinson, Sprayberry. Sixth edition
- Interpretation of Equine Laboratory Diagnostics. Nicola Pusterla and Jill Higgins