PPID in Horses

PPID stands for Pituitary Pars Intermedia Dysfunction and is a degenerative endocrine disorder that disrupts the regulation of hormones produced in the pituitary gland. In the healthy horse, these hormones exist in a strict balance to control a range of functions within the body. In horses with PPID, certain hormones are no longer under this control which can result in problems and ill health. PPID is more commonly seen in older horses, being thought to affect around 20-25% of horses over the age of 15 years (Kirkwood et al., 2022).  Although traditionally termed Cushing’s disease, this disease is different in the horse compared to humans and dogs, and so more recently PPID is considered the correct term to use.

What is the cause of PPID in horses?

The symptoms of PPID in horses are caused by the neurons in the hypothalamus gradually degenerating over time. These neurons are responsible for releasing dopamine to inhibit the production and release of hormones including ACTH (adrenocorticotrophic hormone) from the pars intermedia, which is one of the three lobes of the pituitary gland. This means that insufficient dopamine is released into the pars intermedia and so the signal to stop hormone production is not received. As a result, the pars intermedia continues to produce these hormones, leading to high levels circulating in the body. This leads to some of the common symptoms of PPID, including a longer, curly coat that fails to shed, a dipped-back and pot-bellied appearance, excessive drinking and urination and an increased susceptibility to laminitis. As the disease progresses, the pars intermedia eventually becomes enlarged, compressing the other lobes of the pituitary gland.

shetland with curly coat

What are the symptoms of PPID in horses?

The clinical signs for PPID in horses can include:

  • Longer, thicker coat that fails to shed in the spring
  • A pot-bellied appearance
  • Excessive urination and drinking
  • Lethargy or a change in attitude
  • Poor performance
  • Loss of muscle tone
  • Increased susceptibility to laminitis
  • Regional or abnormal fat deposits
  • Abnormal sweating
  • Increased susceptibility to infections

How is PPID diagnosed in horses?

If you are worried that your horse or pony is showing signs of PPID then you should consult your vet who may carry out a blood test to check for high levels of ACTH. However, it is worth bearing in mind that the reliability of such tests may be limited because ACTH concentrations can vary naturally even in the healthy horse, for reasons including time of year, breed, stress or exercise. For example, a study in 2023 identified that ACTH levels are typically higher in the autumn compared to in the spring, and that in the autumn only, ACTH levels in ponies are typically higher than in Thoroughbreds (Bamford et al., 2023). It has also previously been noted that Arabs and donkeys have higher ACTH levels compared to other breeds, especially between the months of May and November (Durham et al., 2022). However, this does remain the best method for PPID diagnosis, and your vet will be able to advise in more detail regarding the possible limitations and implications of your horse’s test results and the best course of action to take going forward.

In the future, more common diagnostic techniques could include methods such as computed tomography (CT) or magnetic resonance imaging (MRI) to identify changes or abnormalities in the shape and size of the pituitary gland (Kirkwood et al., 2022). However, currently these options are not frequently used due to their high cost and limited availability.

How is PPID treated in horses?

PPID is a degenerative disease and as such if the horse does not receive veterinary treatment, the symptoms of the disease will get worse over time. Veterinary medication is available that usually allows horses to continue to lead a relatively normal life. The only medication licensed for PPID in horses is pergolide mesylate, which is more commonly known as Prascend. This will need to be prescribed by your vet and can help to regulate your horse’s hormone levels by mimicking the action of dopamine in order to reduce ACTH production. As a result, it should help to manage the symptoms that your horse is experiencing. Your vet will advise on an appropriate dosage for your horse, as responses can vary between individuals.

Cushings Pony - Jenny SwainHow should horses with PPID be managed?

The dietary management of horses and ponies with PPID is somewhat dependent on whether they also have underlying insulin dysregulation (ID), as this will influence their susceptibility to laminitis. However, since the link between PPID and ID is not yet fully understood, it is generally considered the safest course of action to manage them in much the same way as a laminitis-prone individual. This means ensuring their diet is low in sugar and starch and avoiding cereal-based feeds, including some that may be marketed for veterans. If weight gain is required, using feeds high in fibre and oil, like Dengie Alfa-A Oil, will be a more appropriate way of providing the extra calories or energy they need.

Grazing may also have to be restricted or avoided, especially during the spring and autumn months. Horses and ponies who also have Equine Metabolic Syndrome (EMS) will be at an even greater risk of laminitis so should be managed accordingly.

A balanced diet is very important as horses with PPID may have a compromised immunity and poor skin condition. If you are feeding less than the recommended amount of a fortified feed or if you’re feeding your horse a fibre-only diet, it’s necessary to add a broad-spectrum vitamin and mineral supplement or balancer to ensure your horse’s diet is balanced. This will provide the key nutrients they need alongside their forage, including antioxidants, to support their immune function and general health.

Good quality protein is also important in the diets for individuals with PPID to help combat muscle wastage. Alfalfa is a great option for this purpose as it is naturally low in sugar and starch but high in good quality protein and essential amino acids. Dengie Alfalfa Pellets, Alfa-A Oil, Alfa-Beet or Alfa-A Molasses Free are all suitable for horses with PPID, depending on their energy or calorie requirements. It may be beneficial to have a conversation with an equine nutritionist for more in-depth advice specific to your horse’s needs.

It’s also a good idea to get in the habit of checking your horse’s weight by both weigh taping and body condition scoring on a regular basis. This is particularly relevant for those with PPID who may have abnormal fat deposits. Regular monitoring can help you to identify any losses or gains sooner rather than later and then implement dietary or management changes to help maintain a healthy body condition.

Other age associated issues, such as dental issues, may also need to be considered. As PPID tends to affect older horses, poor teeth may be an additional problem to overcome. Their forage intake should be monitored so that any changes in appetite can be noted. High-fibre feeds that can be soaked, such as Dengie Alfa-Beet, may be easier to chew and can be used as partial forage replacers.

Horses with PPID can be fussy, which may be in part associated with a side-effect of the medication (Tatum et al., 2020). Offering different types of high-fibre feeds may tempt them to eat. If your horse doesn’t eat much hay in the stable, try offering a bucket of chopped fibre feed alongside to see if you can encourage your horse to eat more fibre. Secondly, try feeds with different flavours or herbs to tempt them. More information on feeding the fussy horse or pony can be found here. It is however important to contact your vet if you notice any changes in your horse’s appetite since introducing any medication.

It is essential to implement a suitable parasite control programme for all horses, but especially for those with PPID as these horses may be more likely to have higher faecal egg counts and be at greater risk of worm burdens (Horner et al., 2024). It should be noted though that blanket worming is no longer recommended due to the increasing resistance to anthelmintics (wormers) and so sustainable worm control practices and a risk assessment should be discussed with your vet or prescriber. More information can be found here. 

Key Takeaways

  • Horses and ponies with PPID should be managed in the same way as those prone to laminitis.
  • Choose feeds low in sugar and starch – this means avoiding cereal-based mixes or cubes, even those targeted at senior horses.
  • For poor doers or those needing weight gain, instead select feeds containing higher levels of fibre and oil.
  • Alfalfa is a great way to supply additional quality protein and slow-release energy/calories as it is low in sugar and starch.
  • Regularly monitor your horse’s weight and body condition to enable any changes to be identified sooner rather than later.
  • For fussy feeders, try adding different herbs or flavours to your horse’s feed to try and tempt them and keep their feed more varied without having to continually change products.
  • Discuss a suitable parasite control programme with your vet.

References

  • Bamford et al., (2023) Investigation of breed differences in plasma adrenocorticotropic hormone concentrations among healthy horses and ponies. The Veterinary Journal296, p.105995.
  • Durham et al., (2022) The effect of month and breed on plasma adrenocorticotropic hormone concentrations in equids. The Veterinary Journal286, p.105857.
  • Horner et al., (2024) Strongyle egg shedding and egg reappearance periods in horses with pituitary pars intermedia dysfunction. Veterinary Parasitology328, p.110176.
  • Kirkwood et al., (2022) Pituitary pars intermedia dysfunction (PPID) in horses. Veterinary Sciences9(10), p.556.
  • Tatum et al., (2020) Efficacy of pergolide for the management of equine pituitary pars intermedia dysfunction: A systematic review. The Veterinary Journal266, p.105562.