Preventing Laminitis: Pituitary Pars Intermedia Dysfunction (PPID)

with Dr Tania Sundra

Principal veterinarian at Avon Ridge Equine Veterinary Services, Western Australia.

Equine pituitary pars intermedia dysfunction (PPID) is the most common endocrine disease in aged horses and ponies. PPID has previously been called Equine Cushings disease, but this is technically not a correct term. It is estimated that PPID affects approximately one-third of all horses over 16 years of age. PPID is a progressive endocrine disorder that affects the pituitary gland, which sits under the brain, specifically the pars intermedia region.

In healthy horses, the production of hormones such as adrenocorticotropic hormone (ACTH) is regulated by the hypothalamus and pituitary gland. However, in horses with PPID, there is a dysfunction in this regulatory system, leading to an overproduction of hormones, including ACTH. This excess of ACTH can result in a range of clinical signs.

PPID and hyperinsulinemia (high levels of insulin in the blood) are two conditions that can significantly increase the risk of laminitis in horses. Studies estimate that approximately 30-60% of PPID cases also have hyperinsulinemia. Management of laminitis has improved over the last few years with the use of drugs like ertugliflozin, but recurrent episodes of laminitis in older horses are often associated with failure to manage the PPID alongside the hyperinsulinemia. By addressing and managing both hyperinsulinemia and PPID, horse owners can reduce the risk of laminitis development in their older horses and ponies.

Clinical signs of PPID

Clinical signs of PPID can vary in severity and may include:
- Abnormal hair coat (long, curly, failure to shed)
- Muscle wastage, particularly along the topline
- Increased thirst and urination
- Weight loss
- Laminitis
- Recurrent infections
- Degenerative changes in the suspensory ligaments
- Delayed wound healing
- Lethargy
- Changes in behaviour or attitude
- Heat intolerance
- Pot belly appearance
- Abnormal sweating
- Increased susceptibility to infections
- Polyphagia (increased appetite)

Recognising these clinical signs and seeking veterinary advice for proper diagnosis and treatment is essential for managing PPID in horses effectively and ensuring their well-being.

Diagnosis

In the diagnosis of equine PPID, measuring basal ACTH levels through a simple blood test is common practice. Interpretation of ACTH levels should take into consideration seasonally adjusted reference ranges, as hormone levels can vary throughout the year. This can make diagnosing PPID challenging. However, a new test is now available for veterinarians in Australia called the Thyrotropin-Releasing Hormone (TRH) stimulation test. This test involves administering TRH to the horse and measuring the levels of ACTH in the blood before and after stimulation. An elevated post-stimulation ACTH level is indicative of PPID. This test is commonly performed to detect early cases of PPID that might be missed if performing a basal ACTH test.

It is important to note that horses without clinical signs of PPID or those younger than 13 years old should not be routinely tested for the condition. Stressful situations, such as pain from laminitis or transport, can also influence ACTH levels, leading to potential misinterpretation of test results.

Monitoring insulin levels in horses with PPID, allows veterinarians and horse owners to assess the risk of developing laminitis and implement preventative measures to manage hyperinsulinemia. Regular measurement of insulin concentrations can help guide treatment strategies, such as dietary modifications, weight management, and medication to control insulin levels. Any horse presenting with laminitis should have insulin concentrations measured in a fed-state or in response to a standardised oral sugar test. Measuring insulin levels in a fasted state is no longer recommended.

Treatment

When it comes to treatment options for equine PPID, a drug called pergolide is most commonly used. Pergolide is a dopamine agonist that helps regulate hormone production from the pituitary gland. It is typically administered orally and has been shown to be effective in controlling clinical signs of PPID. However, like any medication, pergolide can have potential side effects, like dullness and inappetence, which should be monitored closely by a veterinarian. Extended-release cabergoline is an alternative option that can be administered by a weekly intramuscular injection, making it a suitable choice for horses who are unable to be medicated daily or who are difficult to administer an oral medication. Cabergoline is not currently registered for use in horses, and reported side-effects are similar to those of pergolide.

Management

Managing horses with PPID involves a holistic approach that includes various aspects of care. Clipping horses with long hair coats over the summer can help prevent them from overheating and reduce the risk of skin infections. Additionally, regular dental care is essential for older horses, as dental issues can impact their ability to chew and digest food properly.

Feeding older horses with PPID can present unique challenges, particularly when managing weight fluctuations commonly associated with the condition. For older horses with PPID who are overweight or have regional fat deposits, a controlled and balanced diet is essential to prevent further weight gain and reduce the risk of hyperinsulinemia and laminitis. These horses may benefit from a low-sugar, low-starch diet that is high in fibre and essential nutrients to support overall health while managing weight.

On the other hand, for older horses with PPID who are underweight or have muscle wastage, providing a diet with higher energy content and quality protein sources can help support weight gain and muscle development. It is important that insulin levels are measured to ensure the risk of laminitis is not increased when making dietary adjustments. These horses may require additional calories from sources such as high-quality forage, extruded feeds, and supplemental fats to meet their nutritional needs and maintain a healthy body condition.

Tailoring the feeding regimen to the individual needs of each older horse with PPID is crucial for maintaining optimal health and managing weight effectively. Working with a veterinarian or equine nutritionist to develop a customised feeding plan based on the horse’s body condition, metabolic status, and specific dietary requirements can help ensure that they receive the appropriate nutrition to support their well-being and quality of life.

Older horses may also be more susceptible to higher fecal egg counts compared to younger horses. As horses age, their immune system may weaken, making them more vulnerable to internal parasites. It is important for horse owners to be vigilant about monitoring fecal egg counts in older horses and implementing an appropriate deworming protocol in consultation with a veterinarian to help manage parasite burdens and prevent parasite-related disease in aging animals.

Conclusion

Laminitis, especially in older animals, presents a significant threat to equine welfare. By measuring insulin concentrations, diagnosing and managing PPID and hyperinsulinemia, and implementing a comprehensive care plan that includes appropriate treatment, grooming, and nutrition, horse owners can help their horses lead healthy and comfortable lives. Early detection, proactive management, and ongoing support are essential in preventing laminitis and ensuring the well-being of older horses with PPID.

Declarations: This article mentions the use of some medications that are not licensed for use in horses. Please contact your veterinarian for further advice. T Sundra has received subsidised travel expenses to conferences by BOVA, the company who produce some of these medications. 

Dr Tania Sundra is the principal veterinarian at Avon Ridge Equine Veterinary Services in Western Australia. Over the past 4yrs, Dr Sundra has been actively involved in clinical research in gastric and endocrine diseases. She was the lead author on some of the first studies in the world to explore new treatment options for laminitis and PPID.