PPID (Cushing's Disease) in Horses: Nutrition Guide

What Is PPID and Why Does Nutrition Matter?

Pituitary Pars Intermedia Dysfunction — commonly known as PPID or equine Cushing's disease — is one of the most frequently diagnosed hormonal disorders in horses and ponies. It's caused by progressive degeneration of the neurons that regulate part of the pituitary gland, leading to an overproduction of hormones, particularly ACTH.

The consequences ripple through the entire body. Horses with PPID often develop a long, curly coat that fails to shed properly, muscle wasting, a pot-bellied appearance, increased susceptibility to infections, and — most dangerously — laminitis.

While veterinary treatment with pergolide (Prascend) is the cornerstone of managing PPID, nutrition plays a critical supporting role. The right diet can help maintain body condition, reduce laminitis risk, support immune function, and improve overall quality of life. Get the diet wrong, and you risk undermining everything the medication is trying to achieve.

This guide walks you through exactly what, how, and why to feed a horse with PPID.

The Link Between PPID, Insulin Dysregulation, and Laminitis

Before diving into feed choices, it's essential to understand why diet is so important for PPID horses.

Many horses with PPID also develop insulin dysregulation (ID). This means their bodies struggle to manage blood sugar levels properly. After eating sugary or starchy feeds, insulin surges to dangerously high levels. Chronic hyperinsulinaemia is now recognised as a direct trigger for laminitis — the painful, potentially life-threatening inflammation of the sensitive laminae in the hoof.

Not every PPID horse has insulin dysregulation, but a significant proportion do. Your vet can test for this with a simple blood test. If your horse is insulin dysregulated as well as PPID-positive, dietary management becomes absolutely critical.

Even in PPID horses without confirmed insulin dysregulation, a low-sugar, low-starch approach is widely recommended as a sensible precaution.

Core Dietary Principles for Horses With PPID

1. Keep Sugar and Starch Low

This is the single most important dietary rule for a PPID horse. The combined sugar and starch content of the total diet should ideally stay below 10% on a dry matter basis. For horses with confirmed insulin dysregulation and a history of laminitis, some nutritionists recommend aiming for below 8%.

In practical terms, this means:

• Avoiding cereal-based feeds such as mixes and sweet feeds containing oats, barley, maize, or molasses
• Choosing forage carefully — not all hay is low in sugar
• Eliminating sugary treats like apples, carrots, and commercial horse treats (or using them very sparingly)
• Being cautious with grass, which can be high in water-soluble carbohydrates (WSC), particularly in spring and autumn

2. Prioritise Fibre

Forage should form the foundation of every horse's diet, and this is doubly true for PPID horses. Fibre is fermented slowly in the hindgut, producing a steady, gentle energy supply without the insulin spikes caused by sugar and starch.

Good fibre sources include:

• Soaked hay — soaking for 30 to 60 minutes in cold water can reduce the WSC content by up to 30%. Note: it doesn't guarantee a safe level, so testing your hay is still important
• Hay replacers — unmolassed sugar beet pulp, unmolassed chaff, and high-fibre, low-sugar commercial feeds designed for laminitics
• Straw — a small proportion of good-quality barley or oat straw can dilute the overall sugar content of the forage ration, though it shouldn't replace hay entirely due to lower nutrient content

3. Don't Starve Your Horse

Many PPID horses lose topline and muscle condition due to the hormonal effects of the disease. Restricting forage too aggressively — something owners sometimes do out of fear of laminitis — can actually make things worse by depriving the horse of essential calories and protein.

A PPID horse should receive a minimum of 1.5% of their bodyweight in forage per day (dry matter basis). For a 500 kg horse, that's at least 7.5 kg of hay per day. If you need to restrict intake for weight management, use small-hole haynets, trickle feeders, or track systems rather than removing forage entirely.

4. Provide Adequate Protein — Especially Quality Protein

Muscle wasting is one of the hallmark signs of PPID. The hormone cortisol (elevated in many PPID horses) accelerates protein breakdown in muscles. To counteract this, you need to ensure your horse is receiving enough high-quality protein, rich in essential amino acids like lysine, methionine, and threonine.

Good protein sources for PPID horses include:

• Soya bean meal (full fat or hulls) — excellent amino acid profile and low in sugar/starch
• Linseed (flaxseed) — best fed cooked or micronised; also provides beneficial omega-3 fatty acids
• Alfalfa — naturally higher in protein and calcium. Some PPID owners worry about alfalfa causing insulin spikes, but research suggests that the overall glycaemic response to alfalfa is actually low. Small to moderate amounts are generally considered safe for most PPID horses
• Specific amino acid supplements — lysine supplements are widely available and can be a useful top-up

5. Balance the Vitamins and Minerals

PPID horses often have compromised immune systems and may be more susceptible to infections, poor wound healing, and oxidative stress. Ensuring adequate vitamin and mineral intake is therefore especially important.

Key nutrients to focus on include:

• Vitamin E — a powerful antioxidant that supports immune function and muscle health. PPID horses often benefit from supplementation, particularly if they have limited access to fresh pasture (the richest natural source)
• Vitamin C — while horses normally produce their own vitamin C, there's some evidence that PPID horses may benefit from supplementation during periods of illness or stress
• Zinc and copper — essential for immune function, hoof health, and coat quality. Many UK and European forages are deficient in these minerals
• Magnesium — involved in insulin signalling. Some studies suggest magnesium supplementation may support insulin sensitivity, though the evidence in horses is still emerging
• Chromium — sometimes promoted for insulin sensitivity, but the evidence base in equines is limited. Discuss with your vet before supplementing

A broad-spectrum vitamin and mineral supplement or a low-calorie feed balancer designed for good doers or laminitis-prone horses is usually the most practical way to cover these bases.

To make sure you're not guessing, consider analysing your horse's diet with MyEquiBalance to identify any nutritional gaps or excesses specific to your horse's forage and feeding regime.

Managing Grass Intake

Grass is one of the trickiest elements to manage for a PPID horse. Pasture can contain very high levels of WSC — sometimes over 25% — particularly during sunny, cold conditions when the grass is stressed.

Practical strategies include:

• Strip grazing or using a track system to limit the amount of grass available
• Using a grazing muzzle — effective at reducing intake by approximately 80% in most horses
• Turning out when WSC is lowest — typically late evening through to early morning (though this varies with weather conditions)
• Avoiding pasture entirely during high-risk periods if your horse has active laminitis or severe insulin dysregulation
• Replacing pasture time with soaked hay in a dry lot or barn setting

Remember, a lush-looking paddock that's been grazed down to very short grass can actually be higher in sugar than a taller sward. Short, stressed grass concentrates its sugars.

Sample Feeding Plan for a 500 kg PPID Horse

Here's what a practical daily diet might look like for a moderately affected PPID horse in light work, maintaining weight:

This is a general guide only. Every horse is different, and factors such as bodyweight, workload, breed, severity of PPID, and whether insulin dysregulation is present will all affect the ideal ration.

What About Supplements Marketed for Cushing's Horses?

You'll find plenty of supplements claiming to support horses with PPID. Some contain ingredients like chasteberry (Vitex agnus-castus), which has been traditionally used as a herbal remedy for Cushing's symptoms.

The honest truth? There is very limited peer-reviewed evidence that any herbal supplement is effective in managing PPID. Chasteberry has some theoretical basis for action on dopamine pathways, but it has never been shown to be as effective as pergolide in clinical trials.

If your horse has been diagnosed with PPID, work with your vet on appropriate pharmaceutical treatment. Supplements may play a supportive role in overall health, but they should never replace veterinary care.

Monitoring and Adjusting Over Time

PPID is a progressive disease. A diet that works perfectly today may need adjustment in six months or a year. Regular monitoring is essential:

• Weigh your horse regularly using a weighbridge or weight tape
• Body condition score every two to four weeks — pay particular attention to the topline, crest, and ribs
• Have your vet recheck ACTH levels at least annually (or more frequently when stabilising medication)
• Test your hay for WSC, protein, and mineral content whenever you get a new batch
• Watch the hooves — subtle changes in hoof growth, rings, or sensitivity can be early warning signs of laminitis

Key Takeaways

• PPID horses need a low-sugar, low-starch, fibre-first diet to reduce the risk of laminitis
• Don't over-restrict forage — PPID horses often need more protein, not less food
• Soaked hay, unmolassed sugar beet, and a good balancer form the backbone of most PPID diets
• Grass management is crucial and often underestimated
• Vitamin E, zinc, copper, and quality amino acids deserve special attention
• Work with your vet on medication — no supplement replaces pergolide
• Review and adjust the diet regularly as the disease progresses

Feeding a horse with PPID doesn't have to be overwhelming. Stick to the fundamentals — low sugar, high fibre, balanced nutrients — and you'll give your horse the best possible foundation for a comfortable, healthy life alongside appropriate veterinary treatment.