Equine Cushings Disease Explained
Team Marketing | 02.12.20
Cushing’s in a nutshell
Pituitary Pars Intermedia Dysfunction (PPID), most commonly known as Equine Cushing’s Disease, is a benign tumour of the pituitary gland located at the base of the brain. It is named after the neurosurgeon Harvey Cushing who first described it. The tumour affects the horse’s hormonal regulation which results in chronically increased cortisol levels that negatively affect the body in a number of ways. The disease is frequently seen in geriatric horses and is increasingly common as horses are living longer thanks to nutrition and veterinary medicine advances. All equines can be affected with the Cushing’s disease but ponies and breeds such as Morgans and Quarter horses seem to be at greater risk.Symptoms
Horses with Cushing’s Disease can exhibit a variety of symptoms, with an excessively long and curly hair coat that fails to shed in the summer being the most recognisable one. Other symptoms include:- Weight loss due to loss of active back muscle, seen as a swayback and potbelly
- Excessive body fat
- Development of insulin resistance which can lead to laminitis
- Polydipsia/polyuria (excessive thirst/urination)
- Blindness
- Weakened immune system; delayed wound healing, chronic infections
- Behavioural changes such as lethargy
- Reproductive disorders
Mechanisms behind Equine Cushing’s Disease
In order to understand the mechanisms behind Equine Cushing’s Disease we must first understand the hormonal regulation of cortisol as the excessive production of cortisol has many harmful effects on the horse. It is important to note that the hormone cortisol regulates body temperature, appetite, blood pressure, muscle tone and helps the body respond to stress. All these important processes are disturbed if cortisol levels are imbalanced (not within the normal range) and this is exactly what happens in horse’s with Cushing’s Disease as the tumour disturbs the delicate balance of cortisol levels.

Diagnosis
A variety of tests are available to diagnose Equine Cushing’s Disease. These include a blood test to identify hyperglycaemia (high blood sugar levels) and a urinalysis to detect abnormally elevated levels of glucose and ketones in the urine. More specific hormone-related tests might be performed to confirm the diagnosis of Cushing’s disease following a repeat blood test to establish the consistency of high blood sugar. Two conditions that can cause misdiagnoses due to similar symptoms are hypothyroidism and insulin resistance..Treatment
Medical therapy - Treatment can be very successful if the symptoms are caught early, basically returning the horse to normal health for several years. Unlike in humans, removal of the tumour by surgery is not a possible treatment in horses since the pituitary gland is inaccessible. The most common treatment is hormonal replacement therapy, where a drug which works to reduce cortisol production is administered. The most common drug used today is Pergolide. It is important to note that treatment does not cure the tumour but controls its’ growth and treats the symptoms. Management - Management is particularly important for horses with Cushing’s Disease due to the body’s inability to regulate many processes and the reduced immunity. This includes routine hoof care, deworming, vaccinations and dentistry. Horses with excessive hair growth should be clipped in the warmer months to increase comfort and better assess their body condition. Due to the lack of being able to control their own body temperature, it is important to provide a shelter and/or rug in the cooler months of the year.