Some of the most common diseases of older animals do not announce themselves. A horse that looks fine in the pasture in October may already be carrying a hormone problem that shows up as a shaggy coat in winter, a bout of laminitis next fall, or a topline that has quietly thinned. The same name, Cushing's disease, is used for a different condition in older dogs. In both species, the early signs are easy to blame on age.
This guide is written for horse owners and dog owners in Morristown and across East Tennessee. Part 1 covers PPID (pituitary pars intermedia dysfunction, also called equine Cushing's disease): the subtle signs, why autumn matters for testing, and what treatment looks like. Part 2 covers Cushing's disease in dogs and how it differs. It is general educational information, not a substitute for an exam.
Two diseases, one name
Cushing's disease is named for a condition in which the body is exposed to too much of the hormones that the pituitary and adrenal glands control. In horses and dogs, the result can look similar from the outside: a changed coat, a pot belly, muscle loss, more drinking and urinating, and infections that keep coming back. But the underlying disease, the tests, and the treatment are different in each species, and that difference matters when a diagnosis is made.
- Horses: the problem starts in the brain. With age, the nerve cells that normally keep the pituitary in check break down, and the pituitary overproduces ACTH and related hormones. This is PPID.
- Dogs: the problem is excess cortisol, most often from a small pituitary tumor and less often from an adrenal tumor. This is canine hyperadrenocorticism.
Part 1: PPID in horses
PPID is the most common endocrine disease of older horses and ponies. It is most often diagnosed after age 15, although it can start earlier. It is not caused by anything an owner did, and it is not rare. Because it advances slowly, horses and ponies commonly live with it for years before anyone connects the pieces.
The subtle signs owners overlook
Delayed shedding and abnormal coat growth
This is the sign most specific to PPID. A normal horse sheds its winter coat in spring and early summer. A horse with PPID may shed late, shed in patches, hold on to a coat through the summer, or grow a hair coat that is longer, thicker, or wavy or curly, especially along the legs, jaw, and belly. Early on it can be subtle: a coat that never looks sleek, a few stubborn patches, or a horse that sheds weeks after its pasture mates. Owners often put it down to age or poor condition.
Loss of topline muscle and a pot belly
Excess hormones break down muscle. Look at the horse from behind and above: a horse that is losing muscle may have a sunken or sharp topline, a dipped back, and a rounder belly even when the weight on the scale looks fine. Some horses also develop abnormal fat pads over the eyes, along the crest of the neck, or at the tailhead.
Recurrent infections and slow healing
PPID weakens the immune response. Repeated hoof abscesses, skin infections, sinus or dental infections, and wounds that take longer than they should to heal are all common. If you have called a veterinarian or farrier more than once this year for what seems like a string of unrelated problems, it is worth asking about PPID.
Changes in drinking, urination, and sweating
Many horses with PPID drink more and urinate more, so stalls are wetter and buckets empty faster. Some sweat more than the weather explains, or sweat excessively. A change is easy to miss unless you track how often you refill troughs. Our guide to excessive thirst in pets and livestock explains how to measure it.
Laminitis, lethargy, and behavior changes
PPID is one of the leading causes of laminitis in older horses. A horse that has had one episode of laminitis without a clear cause, or that is sore on gravel, shortens its stride, or stands rocked back on its heels, should be checked. Other signs include lethargy, a drop in performance, and a change in attitude. In mares, PPID can interfere with fertility.
Why a horse looks healthy until winter
A horse with early PPID can look fine for most of the year. Summer coats are short, weight can be hidden under a blanket or a round belly, and a quiet horse is not necessarily a sick one. Winter is when the changes become obvious: the coat that should have shed is now a full season thicker than it should be, muscle loss shows against the winter silhouette.
The better time to catch PPID is before that, in the fall. By the time the coat is obvious, the disease has usually been present for a while, and treatment is easier when it starts earlier. We recommend that owners of horses over 15 watch for coat, muscle, and drinking changes every season and mention anything unusual at each visit.
Why autumn matters for testing and interpretation
ACTH, the hormone we measure most often, is not constant through the year. In every horse, ACTH rises naturally in late summer and fall, roughly August through November in the Northern Hemisphere, as the body prepares for winter. In a horse with PPID, that fall rise is exaggerated. This has two practical consequences:
- Interpretation changes by season. A number that is normal in the fall can be abnormal in spring, and the reverse is also true. We read results against seasonally adjusted reference ranges. Comparing a fall result to a spring cutoff can label a healthy horse as sick.
- Fall can be the most sensitive time to test. Because the fall rise is exaggerated in horses with early disease, a fall sample can pick up PPID that a spring sample misses.
Autumn is also a laminitis season for horses with PPID. In East Tennessee, cool-season pastures including fescue regrow in the fall, and sugars can build up in grass after cold nights and sunny days. Horses with PPID are more likely to also have problems handling sugar, which raises laminitis risk further. Our fall health checklist covers fall grass, acorns, and red maple hazards for horses in more detail.
When to test, and what we test
Which horses should be tested
- Any older horse (generally over 15) with delayed shedding, a long or curly coat, muscle loss, or a pot belly
- Any horse with laminitis, especially if the cause is not clear
- Horses with recurrent hoof abscesses, infections, or poor wound healing
- Horses that drink and urinate more than they used to
- Older horses without signs, as part of a yearly wellness exam, because early detection makes treatment simpler
The tests
The standard screening test is a blood sample for plasma ACTH. In some horses, particularly early or borderline cases, we may recommend a TRH stimulation test, in which a second sample is taken after an injection. Because PPID and equine metabolic syndrome often overlap and both cause laminitis, we usually check insulin as well. Samples need careful handling, because ACTH breaks down quickly, and pain, stress, illness, and some medications can raise it, so we choose the timing with that in mind. A veterinarian reading the results with your horse's season, age, and signs gives a more reliable answer than any single number.
Treatment and daily management
PPID is not curable, but it is manageable, and most horses respond well. Treatment usually includes:
- Daily medication. Pergolide, a dopamine agonist and the standard treatment, corrects the hormone imbalance. We recheck bloodwork after starting treatment and adjust the dose to the horse.
- Hoof care. Regular trimming and prompt attention to soreness help prevent and manage laminitis.
- Dental care. Older horses with PPID are prone to dental problems, and good teeth help them hold weight.
- Parasite control. We base deworming on fecal egg counts rather than a calendar.
- Vaccines and wellness exams. Because the immune system is affected, we keep vaccines current and recheck at least yearly.
- Nutrition and body condition. Feed plans depend on whether the horse is also insulin dysregulated. Some horses need a low-sugar diet and managed pasture access. Others need more calories and protein to protect muscle.
- Coat management. Clipping a long summer coat makes horses more comfortable in the heat.
With treatment and good management, many horses stay comfortable and in work for years. More on our horse care page.
Part 2: Cushing's disease in dogs
Dogs get Cushing's disease too, but it is a different disease from PPID. Canine Cushing's disease (hyperadrenocorticism) means the body makes too much cortisol. Most often, about eight in ten cases, a small tumor in the pituitary gland drives the adrenal glands to overproduce it. In the rest, a tumor in an adrenal gland itself is responsible. A dog on long-term steroid medication can also develop Cushing's-like signs, which is a separate issue.
Signs in dogs
Cushing's disease usually appears in middle-aged and older dogs, and breeds such as poodles, dachshunds, Boston terriers, beagles, and boxers are often affected. The signs develop slowly and are often mistaken for aging:
- Drinking and urinating more, including nighttime accidents
- A big appetite and food-seeking behavior
- Excessive panting
- A pot-bellied look and loss of muscle, especially in the hindquarters
- Thinning hair, usually symmetrical, that does not regrow after clipping, with thin skin
- Recurrent skin or urinary infections
- Lethargy and reduced stamina
Autumn is when many owners notice it, because the new winter coat fails to come in or hair loss stands out as the weather cools. Increased drinking in dogs can also point to diabetes, kidney disease, and other problems, so a thorough exam matters. See our thirsty pets guide for how to measure intake at home.
Diagnosis in dogs
Unlike in horses, dogs are tested only when they have signs, because tests can be misleading in dogs that are healthy or ill with something else. Diagnosis usually combines bloodwork and a urinalysis with a specific hormone test, such as an ACTH stimulation test or a low-dose dexamethasone suppression test, and often abdominal ultrasound to look at the adrenal glands. Seasonal interpretation, which is central in horses, is not part of the canine workup.
Treatment in dogs
Most dogs are treated with daily oral medication, most commonly trilostane, which reduces the adrenal glands' cortisol production, and are monitored with periodic hormone tests. Dogs with an adrenal tumor may be candidates for surgery. Left untreated, Cushing's disease raises the risk of diabetes, high blood pressure, blood clots, and infections, so early diagnosis helps. More on our dog care page.
Horses and dogs compared
| Comparison | Horses (PPID) | Dogs (hyperadrenocorticism) |
|---|---|---|
| What goes wrong | Age-related change in the brain's control of the pituitary leads to excess ACTH and related hormones | Pituitary tumor (most cases) or adrenal tumor leads to excess cortisol |
| Typical age | Usually over 15, sometimes younger | Middle-aged to older |
| Hallmark signs | Late or incomplete shedding, long curly coat, muscle loss, laminitis | Thirst, appetite, panting, pot belly, hair loss, thin skin |
| Main tests | Plasma ACTH (with or without TRH stimulation), insulin | ACTH stimulation or dexamethasone suppression test, urine tests, ultrasound |
| Seasonal interpretation | Essential, ACTH rises naturally in fall | Not part of the workup |
| Usual treatment | Pergolide plus hoof, dental, parasite, and nutrition management | Trilostane, or surgery for some adrenal tumors |
| Biggest risk | Laminitis and infections | Diabetes, infections, high blood pressure |
Large animal care in Morristown and East Tennessee
If you are looking for a large animal veterinarian in Morristown, TN, our veterinarians practice mixed animal medicine and travel to farms across East Tennessee. Dr. Jacob Harris has a special focus on bovine and equine care, and Dr. Matthew Harlan focuses on ambulatory and emergency care. For a horse with possible PPID, a visit usually covers a physical exam with attention to coat, muscle, and hooves, a review of your horse's history and seasonal changes, blood sampling, and a plan we can carry out at your barn. We also care for cattle, goats, sheep, and pigs, and for dogs and cats at the clinic.
Frequently asked questions
What is PPID, or equine Cushing's disease?
PPID stands for pituitary pars intermedia dysfunction. It is an age-related change in the part of the brain that controls the pituitary gland, which leads the pituitary to overproduce several hormones, including ACTH. It is the most common endocrine disease of older horses, and it is the condition people usually mean when they say a horse has Cushing's disease.
How old are horses when they develop PPID?
PPID is most common in horses over 15, but it can appear in middle-aged horses, and signs sometimes start in the early teens. Any horse that is older, or that has unexplained laminitis, a coat that does not shed, or muscle loss, is worth testing regardless of age.
How do I know if my horse has Cushing's disease?
The most reliable early clues are a coat that sheds late, incompletely, or not at all, a long or curly hair coat, loss of muscle along the back, a pot belly, recurrent infections or hoof abscesses, increased drinking and urination, and laminitis. Confirming PPID takes a blood test, usually plasma ACTH, interpreted with seasonal reference ranges.
When is the best time to test a horse for PPID?
ACTH is naturally higher in all horses in late summer and fall, and horses with early PPID show an exaggerated rise, so fall testing can be more sensitive. The result must be read against fall-specific reference ranges, which is why we interpret the number by season rather than against a single cutoff.
Can Cushing's disease in horses be cured?
No, but it is very manageable. Most horses are treated with a daily oral medication, pergolide, along with good hoof, dental, parasite, and nutrition management. We recheck bloodwork after starting treatment and adjust the dose. Many horses stay comfortable and rideable for years.
Does PPID cause laminitis?
It can. PPID is one of the leading causes of laminitis in older horses, and the risk rises in the fall. Heat in the hooves, a bounding pulse at the pastern, reluctance to walk or turn, and standing rocked back on the heels are reasons to call the same day.
Do dogs get Cushing's disease too?
Yes, but it is a different disease. Canine Cushing's disease, or hyperadrenocorticism, means the body makes too much cortisol, usually because of a small tumor in the pituitary gland or, less often, a tumor on an adrenal gland. It is diagnosed and treated differently from PPID in horses.
What are the signs of Cushing's disease in dogs?
Increased thirst and urination, a big appetite, panting, a pot-bellied look, thinning hair or hair that does not grow back after clipping, thin skin, muscle weakness, and recurrent skin or urinary infections. It is most common in middle-aged and older dogs.
Do you have a large animal veterinarian in Morristown, TN who sees horses?
Yes. Tennessee Valley Veterinary Services provides mixed animal care in Morristown and across East Tennessee, including ambulatory farm calls for horses, cattle, goats, sheep, and pigs, along with care for dogs and cats.
When to call us right away
Do not wait for these
- A horse with heat in the hooves, a bounding pulse at the pastern, reluctance to walk or turn, or standing rocked back on its heels
- A horse with signs of colic, such as pawing, rolling, or looking at its flank
- A horse with dark urine, pale or yellow gums, and lethargy
- A dog that collapses, vomits repeatedly, or is suddenly weak or unable to walk normally
- Any animal that stops eating or drinking, or is struggling to breathe
Emergency services are available for our farm animal patients after-hours and on weekends. Call (423) 438-3864. For dogs, cats and other companion animals after hours, see our emergency care information.
Schedule a wellness exam for your older horse or dog
If your horse is over 15, or your dog is middle-aged or older, a fall exam with bloodwork is a good time to look for early disease. Through October 31, 2026, our Grand Opening Specials include a free stool sample with every visit, which gives us what we need for a parasite check. Book an appointment or call (423) 438-3864. Prefer to text? Send a message to (423) 820-8939.
Further reading
Trusted references: American Association of Equine Practitioners, Merck Veterinary Manual, and American Animal Hospital Association. Related reading from us: Summer to Fall: A Clinical Health Checklist for Pets and Livestock in East Tennessee and Thirsty Little Monsters? What Excessive Water Drinking Means for Pets and Livestock.
This article is general educational information and does not replace a veterinary exam. Every animal is different. If your animal is sick, call us or an emergency veterinary service right away.
