Disorders of the endocrine system can significantly impact the health and performance of horses. Understanding the endocrine system and what happens when things go awry is essential for horse owners to support their horse’s long-term health.
Key Takeaways
- The endocrine system is made up of multiple glands that produce hormones that send signals to other tissues in the body to help it perform critical functions.
- Disorders of the endocrine system are common in horses and can lead to significant health and performance issues.
- The most recognized endocrine disorders in horses are PPID and EMS.
- Early recognition and proper management with the help of a veterinarian are key to keeping your horse healthy and performing their best.
What Is an Equine Endocrine Disorder?
The endocrine system is made up of various glands, including the adrenal and pituitary glands. These glands produce hormones, which are signal molecules that bring messages to tissues and organs within the body. They help direct and regulate many critical body functions of the horse, including:
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Metabolism
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Immune response
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Reproduction
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Stress
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Growth
An endocrine disorder is any disease or dysfunction of the glands within the body that produce hormones. Hormones affect almost all tissues, including the:
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Gastrointestinal tract
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Reproductive tract
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Skin
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Muscles
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Immune cells
Disruption of the function of these hormones can have many negative side effects in horses, including:
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Poor healing
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Low energy
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Weight gain
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Infertility
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Common Endocrine Disorders in Horses
Pituitary Pars Intermedia Dysfunction (PPID / Equine Cushing’s Disease)
Pituitary Pars Intermedia Dysfunction (PPID), also known as equine Cushing’s disease, is a dysfunction of the pituitary gland.
The pituitary gland primarily secretes a hormone called adrenocorticotropic hormone (ACTH). ACTH plays a role in the body’s response to stress.
PPID is an age-related syndrome in which a benign tumor grows within the pituitary gland of the horse, causing it to produce more ACTH than it should.
Excess amounts of this hormone circulating in the blood can have various side effects. Some common clinical signs may include:
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A long and curly hair coat
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Weight and muscle loss
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Decreased energy
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Frequent infections
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Regional adiposity (or “cresty neck,” fat pads)
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Laminitis
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Frequent tendon and ligament injuries
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High intestinal worm burdens
Diagnosis of PPID involves a thorough physical exam and history performed by a veterinarian, followed by blood tests. The most common tests used to help diagnose PPID include:
These tests are aimed at determining if too much ACTH is being produced by the pituitary gland.
There is no cure for PPID in horses, so once a diagnosis has been made the treatment primarily focuses on managing symptoms. The primary treatment for PPID is a medication called Prascend (pergolide mesylate).
The horse will need this medication for the rest of their life once PPID has been diagnosed, and the dose may need to be adjusted periodically as the pituitary changes advance.
Hypothyroidism
Hypothyroidism is a rare condition in horses in which the thyroid gland does not produce enough thyroid hormones.
Hypothyroidism has historically been over-diagnosed in horses. Many of the symptoms of hypothyroidism are similar to those seen in EMS (poor hair coat, weight gain) and veterinarians often believed that some of these symptoms were at least partially due to low circulating thyroid hormone levels.
However, blood tests for thyroid hormone have shown that these levels fluctuate greatly throughout the day, and therefore can be unreliable for diagnosing hypothyroidism.
The most reliable tests to determine if a horse truly has hypothyroidism include:
These tests essentially rule out thyroid function as a component of a horse’s endocrine disease.
In rare cases where hypothyroidism is diagnosed in an adult horse, a veterinarian may prescribe levothyroxine (Thyro-L) and recommend dietary management.
Hypothyroidism in Foals
Hypothyroidism, although not a significant factor in the adult horse, is more common in foals.
Foals born to mares who have been fed diets high in iodine while pregnant are susceptible to hypothyroidism because their thyroid gland is immature in utero and cannot process the iodine appropriately. This can lead to:
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Delayed ossification (hardening) of small bones in the limbs
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Mandibular prognathism (inappropriate jaw development)
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Respiratory distress
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Dysmaturity (underdevelopment)
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Goiter (an enlarged thyroid gland)
Since the hypothyroidism is experienced in utero, most of the damage is already done before birth. The only care possible once the foal is born is supportive care, including supportive bandages and oxygen therapy. These conditions can be life-threatening in severe
Diabetes Mellitus
Diabetes mellitus (DM) is similar to EMS, as both are related to insulin dysregulation.
With EMS, the pancreas produces insulin normally but the body’s tissues don’t respond to it, leaving too much insulin circulating in the blood. In DM, the pancreas is not producing enough insulin, resulting in too much glucose in the blood.
DM is very rare in horses and typically occurs secondary to other conditions, including:
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PPID
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Chronic pancreatitis
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Granulosa cell tumors
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Pregnancy
Clinical signs of diabetes mellitus in horses may include:
In confirmed cases of DM, treatment includes dietary management, exercise, and insulin
Diagnosis of Endocrine Disorders
Endocrine disorders are common in horses and can play a large role in a horse’s welfare and performance. Early detection is extremely important to avoid some of the more serious consequences, such as laminitis.
Diagnosis typically involves a thorough evaluation by a veterinarian and routine screening blood tests including insulin, glucose, and ACTH testing.
Treatment and Management Strategies
In addition to the treatments mentioned, nutritional management is one of the key elements of treating PPID and EMS in horses. In obese horses, especially, low-NSC diets, exercise, and calorie management are often recommended.
All horses with endocrine disorders should be monitored closely for:
Routine veterinary checks will help to make sure your horse stays as healthy as possible over the course of their life.
Preventive Measures and Owner Education
Although endocrine disorders cannot be completely avoided, there are some things you can do to help keep your horse healthy for as long as possible. These include:
Monitor your horse closely for early signs of disease including:
If you have any new concerns, it is always a good idea to have your horse evaluated by a veterinarian.
Endocrine diseases are common among horses, and many horse owners will deal with one at some point during their equine career. These are lifelong conditions that require lifestyle management and sometimes medications.
It’s important to treat every horse as an individual and to work closely with your veterinarian to ensure you can make the best care plan possible for your equine companion.
