Cushing’s Disease & Pituitary Health
By: Dr. Lydia Gray
Updated January 26, 2021
What is Cushing's Disease in Horses?
Equine Cushing’s Disease is more accurately known as Pituitary Pars Intermedia Dysfunction aka PPID. It is a collection of clinical signs such as hair coat changes, weight and muscle loss, laminitis, and others due to overproduction of certain pituitary hormones. PPID is a common endocrine (hormonal) disorder of older horses and ponies and has been described as one of the most common diseases in all ages of equine.
PPID occurs in all breeds and both genders, with increasing age as the only proven risk factor. It is diagnosed in approximately 30% of horses over 30 years of age and 20% of horses over 20 years of age and is uncommon in horses less than 15 years old. However, it has been documented in horses as young as 5 years old, in rare cases.
What Causes Equine Cushing’s Disease?
Normally the hypothalamus at the base of the brain regulates the activity of the nearby pituitary gland, including the production of certain hormones for use throughout the horse’s body. However, in PPID chronic damage from oxidative stress to the hypothalamus allows the pituitary gland to operate unchecked, resulting in excessive production of these hormones. The result is subtle, early-stage clinical signs as well as obvious, advanced-stage clinical signs across a number of body systems. The most recognizable of the advanced signs is “hypertrichosis,” a long, sometimes curly, hair coat that fails to shed.
How is Cushing’s Disease in Horses Diagnosed?
How do owners first recognize Cushing’s Disease in their horse?
Once a horse displays the shaggy hair coat characteristic of PPID, the disease has already progressed into an advanced stage. Therefore, horse owners should become familiar with the early signs since the sooner a horse is diagnosed and treatment started, the better its chances of responding to medication and management, thereby improving its quality of life.
According to the 2019 Recommendations for the Diagnosis and Treatment of Pituitary Pars Intermedia Dysfunction from the Equine Endocrinology Group (EEG), early and advanced signs of PPID in horses are:
- Changes in attitude or lethargy
- Decreased performance
- Regional hypertrichosis (excessive hair growth)
- Delayed hair coat shedding
- Loss of topline muscle
- Abnormal sweating (increased or decreased)
- Ligament and tendon inflammation
- Regional fat deposits
- Dull attitude
- Inability to perform at the normal level
- Generalized hypertrichosis (excessive hair growth)
- Loss of seasonal hair coat shedding
- Dipped back (topline muscle atrophy)
- Rounded abdomen (bottomline muscle atrophy)
- Abnormal sweating (increased or decreased)
- Increased drinking and urination (PU/PD)
- Recurring infections
- Dry eye/recurring corneal ulcers
- Increased mammary gland secretions
- Tendon and suspensory ligament laxity
- Regional fat deposits (e.g. above the eye)
- Laminitis and recurring sole abscesses
How is Equine Cushing’s Disease related to Equine Metabolic Syndrome?
When testing a horse for PPID, experts recommend also testing for Equine Metabolic Syndrome, a separate but potentially related endocrine condition that can complicate things. EMS, as it is known, is a collection of endocrine and metabolic abnormalities that increases a horse’s risk of developing laminitis. The hallmark sign of EMS is “insulin dysregulation,” which includes:
- hyperinsulinemia (high levels of insulin in the blood, HI) and
- insulin resistance (the failure of cells to respond to insulin, IR)
Another typical feature of EMS is an all-over obesity and/or localized areas of fat under the skin, known as regional adiposity. A “cresty neck” is one common place for these fat deposits.
Not only can Cushing’s Disease and Equine Metabolic Syndrome occur in the same horse at the same time, PPID is known to exacerbate EMS. Plus, if an EMS horse is determined to also have a separate pituitary dysfunction like Cushing’s, it may do better on medication for that disease (pergolide). Likewise, if it is determined that a Cushing’s horse also has EMS, then a more appropriate diet can be followed. To read our article about EMS, click here.
How do veterinarians diagnose Cushing’s Disease in horses?
PPID can be one of the more challenging diseases for vets to diagnose in horses, especially in the early stages when the clinical signs are subtle (e.g. change in attitude or lethargy, decreased performance, weight and/or muscle loss). Therefore, when horse owners first notice a difference in the health or behavior of their horse – or the vet picks up on something during a routine visit such as a Coggins test or health certificate – a more thorough evaluation should take place that includes patient history, physical exam, and bloodwork.
When a veterinarian “takes a history” on a patient, it means they are having a conversation about an animal’s previous health and behavior compared to changes that have been noticed recently. This dialogue includes everything from diet, exercise, medications, and supplements to daily habits, attitude, and appearance. That’s why it’s important the vet speak to the person or people who know the horse best. Being prepared with the horse’s medical records, training journal, and other documents is also very helpful.
A thorough visual and hands-on assessment of the horse is a key component of the PPID diagnosis, especially in the early stages. The veterinarian may be able to pick up on subtle differences from the last evaluation, such as:
- the beginnings of fat deposits
- slight loss of muscle over the topline
- tenderness to hoof testers over the soles of the feet
- mild pain to palpation of tendons and ligaments in the legs
- other key indicators of the initial stages of Cushing’s Disease
Based on the history and clinical signs, the veterinarian may recommend one or more blood tests to rule in or rule out PPID as well as assess insulin status. Some tests are static, requiring only one sample (such as resting ACTH and resting insulin), while others are dynamic, requiring both “before” and “after” samples (such as the TRH Stimulation Test and the Oral Sugar Test).
Which tests are recommended depends on a number of factors, including time of year, whether the disease is in early or late stages, etc. The Equine Endocrinology Group (EEG) regularly updates testing recommendations based on the latest research, publishing a diagnostic flow chart for vets to use.
Treatment of Equine Cushing’s Disease
According to the EEG’s flow chart, horses with a history and clinical signs of PPID and whose ACTH blood levels are above the normal range for the season in which testing occurred should be put on the prescription medication pergolide. The brand Prascend® is the first and only FDA-approved treatment for the control of the clinical signs of PPID, improving the horse’s quality of life but not necessarily extending their lifespan. Although pergolide does not “cure” PPID, it does slow progression and lessen clinical signs, even changes in hair coat and muscling. Starting a horse on prescription medication as soon after diagnosis as possible may also help reduce the risk of serious medical problems such as laminitis, tendon and ligament injury, recurring infections, and other issues.
Some horses will begin to show improvement in clinical signs in as little as one month after starting Prascend, although others may take two or three months to show benefits. The veterinarian will monitor the case closely and advise when it is time to repeat blood tests to see if the medication is also having an effect internally.
Owners should let the vet know if they notice any side effects of the pergolide, such as lack of appetite. Since this is one of the more common adverse reactions, there is an established protocol for getting the horse back on feed and back on medication.
Managing Cushing’s Disease in Horses
Medication is just one component of treating the horse diagnosed with PPID. To provide the best overall outcome, horse owners need to work closely with the veterinarian in all aspects of the horse’s life including wellness or preventive care, the feeding program, and the exercise regimen. This is especially true if the horse has also been diagnosed with EMS or insulin dysregulation, or has other health conditions such as laminitis, increased susceptibility to infections, tendon or ligament issues, and so on.
Special attention should be given to the wellness program and overall supportive care of horses diagnosed with PPID. Not only are the majority of horses with Cushing’s Disease 15 years of age or older and therefore likely experiencing other age-related issues, the effects of PPID itself may require additional maintenance.
Dental care, vaccinations, parasite control, physical exams, and even hoof care all need to be undertaken with particular care in senior horses. As systems – such as the immune system – start to decline, these horses can be more prone to tooth and gum disease, infections, parasitism, sole abscesses, and other health problems. This is even more true when the aging horse has PPID.
In addition to stepped-up veterinary and farrier care, horse owners themselves will need to be more observant of the Cushing’s horse and prepared to increase the level of care from season to season.
For example, in warm summer months, horses with long and shaggy haircoats may need body clipped to remove unshedded winter hair. Learn more about how to clip your horse here. Because shade and moving air can also aid in cooling, horses with access to barns or run-ins may appreciate fans and sun-blocking curtains. Horses naturally cool themselves by sweating (like people do), so supplementing with salt and electrolytes is encouraged to help replace fluids and minerals lost in sweat.
On the other hand, cold weather may call for blankets, shelter, and deeper bedding for horses with Cushing’s Disease that struggle to maintain body condition when temperatures drop. Additional calories in the form of extra hay provide the supplemental energy horses need to stay warm when it’s cold, wet, and windy. Since it’s especially hard for a thin horse to thermoregulate, owners may want to score their horse’s body condition every two to four weeks to stay on top of weight loss.
As horse age – and particularly if they lose weight, become unsound, or develop a medical condition like PPID -- they may slowly lose their place in the herd pecking order. Since this could result in limited access to food, water, and shelter, owners should pay attention to any change in social status and be prepared to adjust the horse’s lifestyle as needed. An adjustment to the exercise program as well as to tack may also be in order if loss of topline muscle (a common sign of Cushing’s Disease), results in saddle fit issues.
Horses with Only PPID
For horses that test positive for PPID but not for insulin abnormality (ie EMS), no nutritional changes may be necessary if the current diet is based on high-quality forage; complete and balanced; and appropriate for the horse’s age, weight, and any other existing health conditions. Overweight/obese horses (or underweight horses) with Cushing’s Disease should have their diets reviewed by an equine veterinarian well-versed in nutrition or by a certified nutritionist since it can be challenging to keep horses with this condition at their ideal weight.
Horses with PPID and EMS
Horses that test positive for Cushing’s as well as some form of insulin dysregulation such as insulin resistance (IR) or hyperinsulinemia (HI) likely need their diets adjusted. For the overweight horse struggling with both endocrine conditions (Cushing’s and EMS), the EEG provides this advice for trying to reduce body fat:
- Limit calories (use a ration balancer or multi-vitamin instead of grain)
- Feed hay with low (12%) NSC or non-structural carbohydrates ie sugars and starches
- At least at first, do not allow any access to grass, even with a muzzle
- Consider whether even low NSC treats are appropriate during the weight loss period
- Add controlled exercise if the hooves are stable and the vet approves it
Later, when the weight has come down, the bloodwork is improving, and there are no signs of laminitis, some limited pasture and low NSC treats may be acceptable. Options for limiting pasture include using a muzzle, restricting by time, or setting up strip grazing or a track system.
Giving daily oral medication to horses can be challenging, especially when dealing with a PPID horse who may be suffering from one of the common side effects of pergolide administration: a loss of appetite. Some horses willingly eat pills mixed in their regular meal, although it may be best to offer medication separately as a “treat” to ensure it was not left in the feed tub, pushed out onto the ground, or spit out. One option is to use treats specially made for this purpose with soft centers surrounded by hard outsides that pills can be “mashed” into. Another option is to find a treat that the horse already likes and hide or mask the pill in it. Some owners will core a hole in a hard treat like a carrot or apple while others opt for soft treats like prunes or dates.
Supplement selection for horse with PPID, EMS, or both must be thoughtful and done in consultation with the vet. In addition to the previously mentioned electrolytes for heavy sweaters and a multi-vitamin instead of fortified grain, other categories to consider include amino acids (protein) to help rebuild topline muscle, omega 3 fatty acids, and vitamin E to bridge the gap between fresh grass and dried forage, and antioxidants to help combat oxidative stress. In addition, there are “specialty” supplements that combine in one product ingredients to support a horse’s metabolic or pituitary health. There is even a category of supplements developed for laminar health.
Controlled activity for the PPID horse needs to be just as tailored to the individual as the preventive care and diet. Otherwise healthy animals diagnosed with Cushing’s that are responding well to treatment and management are encouraged to continue with their regular exercise program. Cushing’s and/or EMS horses with a history of laminitis should gradually return to exercise under a veterinarian’s direction.
Many owners ask: Can I ride my horse with Cushing’s? It can depend on a variety of factors. Structured exercise is highly recommended for horses with either or both conditions that are overweight or obese, as long as the feet are stable and there are no other soundness issues. The EEG has specific guidelines for the level, duration, and intensity of workouts. However, most experts agree that all levels of exercise (walk, trot, and canter; ridden and unridden) are likely to be help reduce weight and improve insulin sensitivity in horses with insulin dysregulation (IR and HI).
Pituitary Pars Intermedia Dysfunction (PPID), also known as Equine Cushing’s Disease, can be challenging to recognize, diagnose, and manage. A horse’s best chances for a successful outcome hinges on:
- increased owner awareness of the early and advanced clinical signs of the disease;
- veterinarian confirmation through history-taking, physical exam, and blood testing; and
- a coordinated management plan
While there is an FDA-approved treatment for PPID, it is not a cure. It is also unlikely a horse’s lifespan can be prolonged. However, administering Prascend (pergolide) – along with wellness care, appropriate nutrition, and controlled exercise -- may slow progression of the disease and improve the horse’s quality of life.
SmartPak strongly encourages you to consult your veterinarian regarding specific questions about your horse's health. This information is not intended to diagnose or treat any disease, and is purely educational.