Pituitary Pars Intermedia Dysfunction (PPID) — conventionally known as Equine Cushing’s Disease — is a progressive endocrine disorder commonly recognized in older horses. The condition develops when cells in the intermediate lobe of the pituitary gland undergo hypertrophy, hyperplasia, or form functional tumors (adenomas). This overstimulation causes the pituitary to release abnormally high levels of adrenocorticotropic hormone (ACTH) alongside other biologically active peptides (such as MSH, beta-endorphins, and CLIP). These hormones trigger an overproduction of cortisol from the adrenal glands, which impacts the horse’s systemic metabolism, muscle mass, immune function, and regulation of tissue inflammation.

Because PPID fundamentally disrupts how a horse metabolizes nutrients, individualized dietary management is just as crucial as veterinary medication (such as pergolide) in supporting a PPID horse’s quality of life.

 

Disclaimer: It is important to work with your veterinarian to properly diagnose, monitor, and manage PPID, including monitoring ACTH levels as appropriate. Nutrition and lifestyle management can play a significant role in reducing the severity of some clinical challenges. However, nutrition cannot reverse the underlying disease or replace veterinary treatment. Pergolide is currently the only medication proven to directly treat the underlying pituitary dysfunction associated with PPID. Nutritional and herbal strategies are supportive measures, not substitutes for appropriate veterinary care.

 

The First Step: Assessing Weight and Insulin Status

 

There is no single “PPID diet.” Instead, your starting point must be guided by two critical factors: your horse’s current body condition score (BCS) and their insulin status.

While PPID and insulin dysregulation (ID) frequently coexist — significantly raising the horse’s threshold for developing devastating laminitis — not all PPID horses are insulin dysregulated. Likewise, some PPID horses are “easy keepers” struggling with obesity, while others suffer from muscle wasting and struggle to keep weight on.

If you are thinking an ACTH test is in your horse’s future, ask your vet about testing insulin sensitivity as well. ID and PPID are not always a package deal, and an ID diagnosis (or not) can drastically change how we can care for PPID horses.

 

1. For the Insulin Resistant or Overweight PPID Horse

If your horse is overweight (BCS ≥ 6/9) and has insulin dysregulation, the primary goal is to safely promote weight loss to normalize insulin sensitivity.

• The Forage Foundation: Feed a strict forage-based diet composed of low-energy grass hay with a non-structural Ccrbohydrate (NSC) content under 12%. For horses with marked fasting hyperinsulinemia, look for hay with under 10% NSC to prevent post-feeding insulin spikes.
• Pasture Restrictions: Limit grazing time or use a grazing muzzle during pasture turnout, as grass carbohydrates can fluctuate wildly. In some severe clinical cases, the horse must be kept off pasture entirely.
• Fortify with a Balancer: Restricted hay diets lack essential trace minerals. Feed a low-NSC, low-inclusion balancer to ensure they receive vital nutrients without added starch or calorie-dense grains. It can be helpful to work with a nutrition advisor or nutritionist to establish what your horse actually needs.

 

2. For the Underweight or Thin PPID Horse

When you are testing your horse for PPID, it is also very helpful to test for insulin sensitivity to best inform the nutritional management strategies — because feeding plans, especially for weight gain, can contrast wildly depending on if your horse is insulin resistant or not. Older horses with PPID frequently struggle with poor body condition due to dental senescence, muscle atrophy, or metabolic inefficiency. Feeding them presents a unique clinical challenge, and if they are insulin resistant, it changes how we can supply more calories without exacerbating insulin resistance.

• The Caloric Balance: Do not rely solely on ultra-high-fat diets. Studies indicate that a very high-fat ration (providing 30% of digestible energy as fat) can actually impair glucose tolerance in aged, non-obese horses. Conversely, a moderate carbohydrate intake (such as 31% NSC) can improve glucose clearance.
• The Multi-Source Approach: It is highly advisable to promote weight gain by combining high-quality fibre, moderate carbohydrates, and safe fats. 
• Dental Considerations: If missing teeth or “quidding” (dropping partially chewed hay) is an issue, replace long-stem forage with soaked feeds like beet pulp or hay cubes/pellets fed in small, frequent meals.

 

Key Nutrients to Monitor & Supplement

When customizing a PPID ration, pay close attention to these vital nutrients to address tissue repair, muscle wasting, and immune suppression:

 

1. Protein and Amino Acids (Epaxial/Gluteal Muscle Wasting)

Sarcopenia, the loss of skeletal muscle mass, is a classic clinical sign of PPID, particularly affecting the epaxial muscles along the spine and the gluteal muscles of the hindquarters.

• Because dopamine depletion may be linked to a lack of amino acid precursors, and because older horses absorb protein less efficiently, PPID horses often have higher daily protein and amino acid requirements.
• Supplementing with high-quality protein rich in limiting amino acids, specifically lysine, threonine, and methionine, has been shown to help rebuild lost muscle mass.
• Alfalfa hay or pellets are excellent sources of highly digestible protein and leucine (which stimulates muscle protein synthesis), but alfalfa should generally be restricted to less than 50% of the total diet to prevent mineral imbalances.

 

2. Vitamin C (Immune Support)

PPID-induced cortisol elevations suppress the immune system, making these horses highly susceptible to skin infections, dental abscesses, and slow-healing wounds.

• While healthy horses synthesize Vitamin C in the liver, physical stress and chronic disease can deplete these reserves.
• Therapeutic Dosing: Supplementing with 0.011 to 0.022 g/kg of body weight (approximately 5.5 to 11 grams for a 500 kg horse) of oral ascorbic acid is recommended to bolster immune defense.
• Do not abruptly stop high-dose Vitamin C supplementation. Long-term supplementation down-regulates the horse’s natural liver synthesis, and a sudden halt can trigger an acute rebound deficiency. Always taper the dose down gradually over several weeks.
• Natural Source: Whole-food Rosehips are rich in natural, highly bioavailable Vitamin C (providing ~295 mg per 100g) and contain complementary flavonoids that support tissue repair and capillary strength.

 

3. Vitamin E and Selenium (Antioxidant Defense)

Chronic insulin dysregulation and PPID are associated with systemic, low-grade tissue inflammation (“inflamm-ageing”) and significant oxidative stress.

• Because the degenerative damage to dopaminergic neurons in the brain may be driven by oxidative stress, high antioxidant support is vital.
• Older PPID horses should be fed higher daily levels of Vitamin E than standard maintenance minimums, with recommended rates of 3 to 5 IU/kg of body weight (or roughly 2,000 to 4,000 IU daily for a 1,000 lb horse) using a highly bioavailable natural form (d-alpha-tocopherol succinate).
• Ensure the diet contains adequate Selenium (0.3 ppm in the total diet) to work alongside Vitamin E to support thyroid function, sugar metabolism, and immune health.

 

4. Electrolytes (Managing PU/PD & Hyperhidrosis)

Horses with advanced PPID frequently suffer from polyuria (excessive urination), polydipsia (excessive drinking), and hyperhidrosis (excessive, patchy sweating).

• These clinical signs can quickly lead to systemic electrolyte depletion.
• Ensure PPID horses have constant, unrestricted access to a plain salt block.
• Depending on their core ration, sweat losses, and environmental temperatures, they may require additional daily supplementation of sodium, chloride, and potassium.

 

5. B-Vitamins (Glucose & Energy Metabolism)

• Vitamin B6 (Pyridoxine): Involved in carbohydrate, fat, and protein digestion, B6 is highly useful for PPID horses to balance blood sugar and support thyroid function. Recommended therapeutic dosage is 750 to 1,000 mg daily.
• Vitamin B12: Clinical studies in PPID cases have documented a strong negative correlation between circulating Vitamin B12 levels and the severity of the disease, making B-complex supplementation highly prudent.

 

6. Magnesium and Chromium (Insulin Regulation)

• Magnesium plays an important cellular role in insulin signaling pathways, and lower levels have been linked to insulin resistance. Ensure adequate magnesium intake to support metabolic health.
• While Chromium is frequently marketed for glucose regulation, research studies show mixed results regarding insulin dysregulation, insulin resistance, and Equine Metabolic Syndrome (EMS). While some trials demonstrate improved glucose clearance and insulin sensitivity with specific forms like chromium propionate or chromium yeast, other clinical trials on insulin-resistant or obese/laminitic subjects found no significant metabolic changes

 

Other Considerations

1. Soak Hay with Care: If low-sugar hay is unavailable, soak your hay in water to leach out soluble sugars. Soaking in cold water for 1 hour or hot water for 30 minutes is a practical way to lower the glycemic load, but be sure to feed a balancer to replace any minerals washed away in the water.
2. Encourage Movement: Provided your horse is free of active, painful laminitis, encourage daily movement or light, structured exercise, which is highly effective at stimulating muscle glucose uptake and improving insulin sensitivity.
3. Engage your PPID horse in enriching activities such as positive reinforcement training. Creating training sessions that are predictable, achievable, rewarding, and low in conflict may encourage engagement and activate dopaminergic pathways involved in the brain’s reward and learning systems, particularly those associated with motivation, attention, and reinforcement. Dopamine plays an important role in helping the brain recognize that a particular behaviour has produced a desirable outcome, making that behaviour more likely to be repeated.At the same time, reducing frustration, uncertainty, and perceived threat may decrease sympathetic arousal and activation of the hypothalamic-pituitary-adrenal (HPA) axis. This could mean a lower cortisol response during training, although the magnitude of that effect will vary considerably between individuals and circumstances.For a horse with PPID, this is particularly interesting because the disease involves degeneration of dopaminergic neurons. It’s important not to confuse the dopamine involved in reward and learning with the specific hypothalamic dopamine deficiency underlying PPID. Positive reinforcement isn’t a treatment for PPID, but it may provide valuable mental enrichment while creating a predictable, low-conflict learning environment.And when training involves choice, clarity, and a genuinely motivating reward, it can become an opportunity for enrichment and stress reduction and a potentially lower cortisol response.