Equine Cushings Disease is quite common in the aged horse population, and horse owners often struggle with having an older horse with this condition and how to manage them.
So what is Cushing’s disease?
Cushing disease is a benign tumor of the pituitary gland, which sits just below brain. The tumor does not spread to other parts of the body, but does cause extra hormones (ACTH) to be secreted to the rest of the body resulting in more cortisol being made by the adrenal glands. Cortisol helps horses respond to stress in their environment by changing their metabolism and allowing their body to prepare for a flight or fight response. In a horse with Cushing’s disease the excess cortisol begins to have chronic negative effects on the horse’s metabolism as well as their immune system.
What do horses with Cushings disease look like?
Cushingoid horses are typically older- the average age of diagnosis is 20 years old, although the typical age of onset is younger 12-17 years old; the disease is often not noticed until later. The most typical clinical sign is a long shaggy hair coat that does not shed out in spring or sheds out slower than other horses. Horses with Cushings Disease also get an abnormal fat distribution and often have a cresty neck and periorbital fat (fat deposits just above the eyes that bulge out). Horses will also lose muscle along the
topline and develop a pot belly as seen below. Horses with Cushing’s disease also have a decreased immune system. Cortisol decreases the level of certain types of cells that fight infection in the blood stream. This leads to low grade chronic infections like sinus or tooth root infections or rain rot that just doesn’t seem to go away. Cushingoid horses are also predisposed to foot abscesses and higher levels of parasites.
Horses with Cushing’s disease may have acute severe episodes of laminitis or chronic mild episodes that would only be evident by the horse being more tender footed and possibly divergent rings on the hoof wall. Cushings often causes insulin resistance due to higher levels of glucose in the blood which has been shown to induce laminitis or the rotation of the coffin bone within the hoof capsule.
The current blood tests that are available can be problematic due to natural fluctuation in the hormones produced due to stress or even seasonal variation. Horses may exhibit a normal rise in ACTH and cortisol in the fall. This means that results always need to be interpreted in light of the horse’s history, clinical signs, and environmental situation, including time of the year. The most common test used is to measure ACTH directly with a blood sample. To try and catch more horses that are early in the course of the diease, horses may be given TRH intravenously and a second blood sample may be taken. The spring is the perfect time to test a horse for cushings, and testing may be done at the same appointment as spring shots and teeth.
Currently the only FDA approved treatment for Cushings Disease in horses is Prascend containing the active ingredient pergolide. Side effects of Prascend are minimal, the most common being loss of appetite. Usually it takes about 3 weeks of for owners to report seeing subtle behavior changes, horses often become brighter and more energetic on treatment. About 3/4s of horses will show improvement of clinical signs or blood work within 3 months. After 6 months about 89% of horses will shed out their hair coat and 46% will show improvement in muscle mass.
Extra care for cushingoid horses
Horses living with Cushings Disease may need to be body clipped in the spring and summer to allow them to be more comfortable in the warmer weather. They should also have aggressive treatment of any wounds or skin infections, as well as regular dental care and oral exams. Cushingoid horses also need regular farrier work and need to be monitored for signs of laminitis. Finally fecal egg counts should be done an annual basis to make sure the horse receives the proper deworming protocol. Horses with Cushings Disease may also need extra care in feeding depending on their weight.
Talk with your veterinarian if you have any concerns about caring for your older horse or you think your horse might have Cushing’s disease.
McGowan, T.W. Prevalence, risk factors and clinical signs predictive for equine pituitary pars intermedia dysfunction in aged horses. Equine Veterinary Journal. 2012. pgs 2042-3306.
Rohrbach, B.W. Diagnostic Frequency, Response to Therapy, and Long-Term Prognosis among Horses and Ponies with Pituitary Pars Intermedia Dysfuction, 1993-2004. J Vet Intern Med 2012; 26: 1027-1034.