Recognise the signs of Cushing’s syndrome in horses, understand how PPID is diagnosed and explore how appropriate nutrition can support the health and wellbeing of older horses and ponies.
Cushing’s syndrome in horses, more accurately known as Pituitary Pars Intermedia Dysfunction (PPID), is an age-related condition that horse and pony owners should be aware of. Recognising the early signs of PPID can help owners seek veterinary advice sooner and put appropriate management and nutritional support in place.
PPID affects the normal function of the pituitary gland, which sits at the base of the brain and plays an important role in regulating hormones throughout the body.
What Is Cushing’s Syndrome in Horses?
The condition we commonly call Cushing’s disease or Cushing’s syndrome in horses is known clinically as Pituitary Pars Intermedia Dysfunction (PPID).
The pituitary gland is involved in the control of a number of hormones and physiological processes. With PPID, changes occur in the pars intermedia of the pituitary gland, resulting in abnormal hormone regulation.
The condition was first described in people in 1932 by neurosurgeon Harvey Cushing, who identified a relationship between characteristic physical changes and a tumour affecting the pituitary gland.
In horses, the condition is associated particularly with ageing and can cause a range of clinical signs, including changes to the coat, muscle condition, thirst and urination, immune function and susceptibility to laminitis.
Why Are Older Horses More at Risk of PPID?
As the equine population continues to age, caring for older horses and ponies is an increasingly important part of horse welfare.
Age is one of the clearest risk factors for PPID. While prevalence in the general equine population is estimated to be less than 3%, estimates in horses over 15 years old are considerably higher, at around 20–25%.
A retrospective mortality study carried out at an equine retirement centre in the Netherlands also found PPID in nearly half of the older equines examined, which had an average age of 26 years at death.
This highlights why regular monitoring of older horses is so important. Some signs of PPID can be subtle, particularly in the early stages, and may simply be attributed to normal ageing.
What Are the Signs of Cushing’s in Horses?
Recognising the signs of Cushing’s syndrome in horses can help owners identify changes that may warrant further investigation with their vet.
Common clinical signs associated with equine PPID include:
- Changes to the hair coat, particularly hirsutism (excessive or abnormal hair growth)
- Laminitis
- Abnormal fat deposits
- Muscle wastage and muscle atrophy
- Increased thirst (polydipsia)
- Increased urination (polyuria)
- Lethargy or depression
- Increased susceptibility to disease
Not every horse with PPID will display all of these signs, and the severity can vary considerably between individuals.
Changes to the Horse’s Coat
Changes to the coat condition are perhaps the sign most commonly associated with Cushing’s in horses.
A long, thick or abnormal coat can be a characteristic feature of PPID. However, mild changes, particularly during the early stages, can be difficult to distinguish from the normal changes associated with ageing or seasonal coat growth.
This is why it is important to consider other changes in your horse as well, rather than relying on coat condition alone.
Muscle Loss and Topline Changes
Muscle wastage and atrophy around the neck, back and hindquarters are also seen in older horses.
Some loss of muscle condition is associated naturally with increasing age and may be influenced by factors such as reduced exercise. However, changes in muscle mass and topline can also be associated with PPID.
A noticeable change in your horse's topline should therefore not automatically be dismissed as simply being part of getting older.
Research into objective assessment of muscle loss in older horses is ongoing, including the development of muscle atrophy scoring systems designed to provide an easy-to-use method for owner assessment.
Laminitis and PPID
Laminitis is one of the more serious clinical concerns associated with PPID.
For this reason, recognising potential signs of PPID early is important. Owners should not wait until more severe clinical signs develop before discussing changes in an older horse with their vet.
For more information on Laminitis, take a look at our blog - Understanding Laminitis Risks
How Is Cushing’s Syndrome in Horses Diagnosed?
If you suspect your horse may have PPID, speak to your vet.
Veterinary diagnosis is generally based on a combination of the horse's clinical signs and appropriate blood testing. A basal adrenocorticotrophic hormone (ACTH) blood test is commonly used and may be repeated for confirmation or ongoing monitoring.
Why Can ACTH Levels Vary?
Interpreting ACTH results can be complicated because ACTH levels naturally vary throughout the year.
In all horses, ACTH concentrations increase during late summer and autumn. This seasonal change is associated with decreasing day length and is thought to form part of the horse's natural preparation for winter.
In horses with PPID, this system becomes dysregulated and ACTH levels can be substantially higher.
Seasonal variation therefore needs to be considered when interpreting test results, which is one reason why veterinary assessment is important.
TRH Stimulation Testing
A thyrotropin-releasing hormone (TRH) stimulation test may provide additional diagnostic information and can be more accurate in some circumstances. However, it is not routinely used in every case because of the additional cost and the potential for transient side effects associated with intravenous TRH administration.
Your vet will be able to advise on the most appropriate testing approach for your individual horse.
How Is Cushing’s in Horses Treated?
Once PPID has been diagnosed, veterinary treatment of the condition commonly involves daily oral administration of the dopamine agonist pergolide.
Treatment is generally long term, and ongoing veterinary monitoring is important.
However, medication can present practical challenges for owners. Studies have highlighted issues including administration compliance and palatability, while some horses may experience behavioural or other changes during treatment.
It is important to remember that nutritional support should complement, rather than replace, veterinary diagnosis and treatment.
If your horse has been diagnosed with PPID, any changes to medication or treatment should always be discussed with your vet.
What Should You Feed a Horse with Cushing’s?
Nutrition is an important part of managing the older horse, and targeted dietary support for horses with PPID can be considered alongside veterinary care.
The nutritional needs of every horse are different, so factors such as body condition, workload, forage intake, dental health and any additional conditions should all be considered.
For an older horse with PPID, areas that may be particularly relevant include:
- Maintaining appropriate body condition
- Supporting digestive health
- Providing a balanced diet
- Considering the horse's overall nutrient intake
- Supporting healthy muscle condition
- Managing dietary factors associated with laminitis risk
- Taking the horse's individual veterinary and nutritional needs into account
Supporting Digestive Health
Weight loss is a relatively common clinical finding in horses with PPID, with some reports suggesting it occurs in approximately one third of veterinary examinations.
Maintaining digestive health is therefore an important consideration when supporting an older horse.
The gut microbiome is also an increasingly important area of research. The relationship between the gut and the brain — often described as the gut-brain axis — is being investigated across a range of species in relation to behaviour and neurological function.
Providing appropriate digestive and gut support, including prebiotics and probiotic ingredients where appropriate, may therefore form part of a wider nutritional management strategy for older horses.
Herbal and Nutritional Support for Horses with PPID
Alongside a balanced diet and appropriate veterinary care, some owners choose to provide additional nutritional support through specific herbs and other ingredients.
Adaptogenic Herbs
Adaptogenic herbs are traditionally used to support the body's ability to adapt to physiological challenges and have particular relevance when considering age-related changes.
Ingredients such as Siberian Ginseng and Omicha have traditionally been used in this context.
Another herb of interest is Gynostemma, sometimes referred to as the "Immortality herb". Its active compounds have attracted research interest because of their potential role in metabolic and insulin regulation.
Insulin dysregulation is an important consideration in horses with PPID, particularly because of its relationship with laminitis risk.
Chasteberry and Equine Cushing’s
One of the best-known herbs associated with nutritional support for horses with Cushing’s is Chasteberry, also known as Vitex agnus-castus.
Chasteberry has attracted particular interest because of its naturally occurring compounds associated with dopaminergic activity. This is relevant when considering PPID, as changes in dopamine regulation are involved in the disease process.
Research into Chasteberry and equine PPID is ongoing, and the evidence is not yet definitive. Published studies have reported improvements in some clinical signs, either when Chasteberry preparations are used alone or alongside veterinary approaches.
As with any nutritional intervention, owners should consider the whole horse and discuss appropriate management with their veterinary and nutritional professionals.
Why a Combined Approach Can Be Helpful
PPID is a complex, age-related condition and there is no single nutritional strategy that will be appropriate for every horse.
A holistic approach can include:
Veterinary care
Regular veterinary assessment, appropriate diagnostic testing and prescribed treatment where required.
Dietary management
A balanced diet tailored to the horse's age, body condition, workload and individual nutritional requirements.
Digestive support
Consideration of gut health and appropriate digestive support where required.
Herbal support
Carefully selected herbs may form part of a wider nutritional strategy.
Monitoring
Keeping an eye on changes in coat condition, body condition, muscle mass, behaviour, drinking, urination and general wellbeing.
At NAF, we believe that nutritional support works best when it is considered as part of the horse's overall management plan, rather than focusing on a single ingredient in isolation.
Managing an Older Horse with Cushing’s Syndrome
For owners of older horses and ponies, understanding PPID symptoms and knowing what changes to look out for can make a real difference.
Keep an eye on:
- Changes to the horse's coat
- Muscle loss or changes to topline
- Changes in body condition
- Increased drinking
- Increased urination
- Changes in energy or behaviour
- Recurring or unexplained health problems
- Signs associated with laminitis
If you notice changes that concern you, speak to your vet. Early investigation can help establish whether PPID is involved and ensure that an appropriate management plan is put in place.
Nutritional support can then form part of that wider approach, helping you support your older horse's digestive health, nutritional requirements and overall wellbeing.
Frequently Asked Questions About Cushing’s in Horses
What is Cushing’s syndrome in horses?
Cushing's syndrome in horses is commonly used to describe Pituitary Pars Intermedia Dysfunction (PPID), an age-related disorder affecting the function of the pituitary gland and hormone regulation.
What are the first signs of Cushing’s in a horse?
Early signs can be subtle. Changes to the coat, muscle condition, body condition, thirst, urination, energy levels or general health may warrant further investigation, particularly in an older horse.
At what age do horses develop Cushing’s?
PPID is primarily associated with older horses. Prevalence increases significantly with age, particularly in horses over 15 years old.
Can Cushing’s cause laminitis in horses?
Laminitis is an important clinical concern associated with PPID. If you have an older horse showing signs of laminitis or other potential PPID symptoms, veterinary advice should be sought.
How is PPID diagnosed?
Veterinary diagnosis generally involves consideration of clinical signs alongside blood testing, commonly including an ACTH test. Seasonal variation in ACTH levels needs to be considered when interpreting results.
What should I feed a horse with Cushing’s?
There is no single diet suitable for every horse with PPID. Feeding should be based on the horse's individual nutritional requirements, body condition, forage intake, workload and any other health considerations. Appropriate nutritional support can be used alongside veterinary management.
Supporting Your Older Horse
PPID is an important condition of ageing horses and ponies, but understanding the signs of Cushing’s in horses means owners can be better prepared to recognise changes and seek veterinary advice when needed.
If you suspect your horse may have PPID, always speak to your vet about appropriate diagnosis, treatment and monitoring.
Alongside veterinary care, carefully considered dietary and nutritional support for horses with Cushing’s can form part of a broader management plan designed around the individual horse.
About the Authors
Dr Andy Richardson, Veterinary Director — BVSc, CertAVP(ESM), MRCVS
Kate Hore, Head Nutritionist — BETA ENFAR Nut, RNutr (Animal), R.Anim.Technol (Cert)
Find out more about Andy, Kate and the NAF Technical Team here
Selected References
- Bradaric Z, May A and Gehlen H (2013). Use of the chasteberry preparation Corticosal for the treatment of pituitary pars intermedia dysfunction in horses. Pferdeheilkunde, 29(6), pp.721–728.
- Beech J, Donaldson MT and Lindborg S (2002). Comparison of Vitex agnus-castus extract and pergolide in treatment of equine Cushing’s syndrome. Proceedings of AAEP 2002, p.175–176.
- Hague N, Durham AE, Menzies-Gow NJ (2021). Pergolide dosing compliance and factors affecting the laboratory control of equine pituitary pars intermedia dysfunction. Veterinary Record, 189(1).
- Herbst AC et al. (2022). Development and evaluation of a muscle atrophy scoring system (MASS) for horses. Journal of Equine Veterinary Science, 110, 103771.
- Ireland JL & McGowan CM (2018). Epidemiology of pituitary pars intermedia dysfunction: A systematic literature review of clinical presentation, disease prevalence and risk factors. The Veterinary Journal, 235, pp.22–33.
- Lokman EF, Gu HF, Wan Mohamud WN & Östenson CG (2015). Evaluation of antidiabetic effects of the traditional medicinal plant Gynostemma and the possible mechanisms of insulin release. Evidence-Based Complementary and Alternative Medicine, 2015, 120572.
- Morais LH, Schreiber HL & Mazmanian SK (2021). The gut microbiota-brain axis in behaviour and brain disorders. Nature Reviews Microbiology, 19, pp.241–255.
- Proosdij R van & Frietman S (2022). Retrospective analysis of cause-of-death at an equine retirement center in the Netherlands over an eight-year period. Journal of Equine Veterinary Science, 110, 103824.
- Wuttke W et al. (2003). Chaste tree (Vitex agnus-castus) — pharmacology and clinical indications. Phytomedicine, 10(4), pp.348–357.
