Adrenal Gland Disease in Horses

Adrenal gland disease in horses is not one single diagnosis. The adrenal glands sit near the kidneys and make hormones that help regulate stress response, metabolism, blood pressure, and electrolyte balance. In practice, when pet parents ask about adrenal disease in horses, the condition most often discussed is pituitary pars intermedia dysfunction (PPID), sometimes called equine Cushing's disease. PPID starts in the pituitary gland, but it affects hormone signaling throughout the body and can change how the adrenal system responds.

True primary adrenal disease, such as an adrenal cortex tumor or a pheochromocytoma, appears to be rare in horses compared with dogs and people. These cases may be found only after advanced imaging, surgery, or even at necropsy. Because of that, many horses with hair coat changes, laminitis, muscle loss, or increased drinking are first evaluated for PPID and insulin dysregulation rather than for a primary adrenal tumor.

This distinction matters because the signs can overlap, but the workup and treatment plan may look very different. Some horses need long-term medical management and monitoring. Others may need referral-level imaging or hospitalization. Your vet can help sort out which path fits your horse's age, signs, and overall health.

The most common endocrine condition that gets grouped under adrenal disease in horses is PPID. PPID is an age-related neurodegenerative disorder of the pituitary gland. Loss of normal dopamine control allows the pars intermedia to enlarge and overproduce hormones, including ACTH-related peptides. That hormonal shift is linked with classic signs such as hypertrichosis, muscle loss, abnormal fat distribution, increased drinking and urination, and a higher risk of laminitis.

Primary adrenal disease is much less common. Rare horses can develop adrenal tumors, including tumors of the adrenal cortex or pheochromocytomas arising from the adrenal medulla. These masses may produce hormones, may be nonfunctional, or may cause illness by bleeding, compressing nearby structures, or affecting cardiovascular stability. Because these tumors are uncommon and signs can be vague, diagnosis is often delayed.

Other conditions can mimic adrenal disease too. Equine metabolic syndrome, chronic pain, poor dentition, parasites, kidney disease, liver disease, and chronic infection can all cause weight changes, lethargy, or laminitis risk. That is why your vet usually looks at the whole horse rather than relying on one symptom alone.

Diagnosis starts with a detailed history and physical exam. Your vet will ask about age, hair coat changes, laminitis episodes, drinking and urination, body condition, appetite, infections, and performance changes. In older horses with a delayed-shedding coat or recurrent laminitis, PPID is often high on the list.

For suspected PPID, common tests include a baseline ACTH level or a TRH stimulation test. Sample handling matters, and seasonal reference ranges may be used, so your vet may recommend specific timing or repeat testing if results are borderline. Many horses are also checked for insulin dysregulation, because PPID and metabolic problems can occur together and that combination raises laminitis risk.

Routine bloodwork can help look for inflammation, infection, kidney changes, glucose abnormalities, and other conditions that may mimic or complicate endocrine disease. If your vet suspects a true adrenal mass, referral diagnostics may include abdominal ultrasound, advanced imaging, blood pressure assessment, and hospital-based monitoring. In rare complex cases, diagnosis may require specialty consultation because there is no single screening test that confirms every type of adrenal tumor in horses.

There is no proven way to fully prevent PPID or rare adrenal tumors in horses. PPID is strongly associated with aging, so prevention is really about earlier recognition and better long-term management. Older horses benefit from regular wellness exams, body condition scoring, dental care, hoof care, and prompt evaluation of any delayed shedding, muscle loss, or unexplained laminitis.

Good metabolic management can also reduce complications. Work with your vet to review forage, pasture access, and sugar and starch intake if your horse is overweight, cresty, or laminitis-prone. Horses with PPID and insulin dysregulation often do better when both problems are addressed together.

Daily observation matters. Tracking water intake, appetite, coat changes, hoof comfort, and energy level can help pet parents catch subtle changes earlier. Early testing does not prevent disease from starting, but it can help your vet begin supportive care sooner and may reduce the risk of severe laminitis and other secondary problems.