HEALTH + NUTRITION CPD – MARCH 2026

Nutrition for Metabolism: When Nutrition Matters Most

By Dr. Marga Mas-Fiol DVM PGDip CertAVP MBA MRCVS, D&H Head of Veterinary, Equine Health & Performance and Louise Scott RNutr, D&H Senior Nutritionist & Product Development Manager.

Insulin dysregulation in horses and increased risk of laminitis

ID refers to all causes of ‘excessive insulin response to oral sugars, fasting hyperinsulinemia and insulin resistance³.

PPID, otherwise known as equine Cushing’s disease, is estimated to affect over 20% of horses, ponies and donkeys aged 15 years and above⁴. It’s a progressive, age-related degenerative dysfunction caused by a benign tumour of the part of brain controlling the production of dopamine and adrenocorticotropic hormone (ACTH), resulting in an array of symptoms and abnormalities in glucose and fat metabolism, including their insulin response.

EMS is defined as a collection of risk factors, genetics and otherwise, leading to ID and associated laminitis^2,3. Figure 1 describes how increased laminitis risk is associated with features that might be present across both PPID and EMS, with ID being the key risk factor.

Abnormally high insulin levels (hyperinsulinemia) can be present in both horses with PPID and EMS, whether at rest and/or after a meal^1,3,4. Whilst the precise mechanism is unclear, hyperinsulinemia is a key factor in developing laminitis^2,3. 

A combination of diet, exercise and drug treatment is currently the mainstay of management of hyperinsulinemia in horses and ponies, avoiding an exaggerated insulin response to dietary non-structural carbohydrates (NSC) is a key to reducing laminitis risk^10,13.

What's new in the treatment of insulin dysregulation

There is a number of pharmacological options available, with different mechanisms of actions aimed at either the primary cause of the disease, in the case of PPID, or modulating glucose and insulin dynamics in horses with ID within the EMS phenotype^3,4,10.

• Pergolide mesylate suppresses the growth of the tumour causing PPID: the dosage is titrated to each horse’s response and monitored seasonally according to variations in blood ACTH levels. Pergolide may improve glucose control⁴, yet it is always prescribed alongside diet and exercise changes, especially in PPID horses with excess insulin levels⁴.
• Equine weight loss drugs: levothyroxine can be used to reduce obesity, although its variable success rate has prompted the rise of sodium-glucose co-transporter 2 (SGLT2) inhibitors for the treatment of insulin-associated laminitis and severe ID in horses and ponies^11,12: SGLT2 inhibitors are controlled substances under the FEI list of prohibited substances, and can be used off-label in the UK if other treatments have failed, or for critical cases of severe laminitis^1,10. They are prescribed for at least 3 months, always with ongoing monitoring of body condition and blood work, and adjunct diet, exercise and foot care¹. Current evidence shows that they effectively treat and prevent insulin-associated laminitis, with a substantial improvement in the horse’s quality of life and high rates of satisfaction amongst horse owners¹². However, side effects may occur and more research is needed to fully understand how to manage them and support horses in treatment¹¹: horses might experience a short-term, generally benign rise in blood triglycerides, and increase water intake and urination has been observed in up to 1 in 5 horses¹²; although this has not been associated with dehydration, it highlights how important free access to fresh water is at all times. 

Practical Feeding and Management 

 Monitoring weight and maintaining a healthy body condition is key for all horses, but especially so for those with PPID and EMS. Hyperinsulinemia may feature in both conditions, and whilst EMS horses often present with a degree of obesity, many PPID horses might have a low body condition score. Regional adiposity is a common feature where abnormal fat deposits appear along the crest of the neck or behind the eye sockets, so it is important to carefully evaluate the overall condition of the horse and not just one area.  Regularly examine body condition by running your hands over the different areas of the horse and use the chart in figure 2 to determine their current condition. 

Grazing and forage management for horses with insulin dysregulation

 For horses with insulin dysregulation, it is often recommended to restrict or eliminate access to fresh pasture, as fresh grass is often rich in sugar which can exacerbate hyperinsulinemia. It is also difficult to regulate how much a horse is eating when in the field, with many good doers overeating when they have unrestricted access to grazing. Restricting grazing time alone might not be effective to limit intake with many horses gorging during the shorted grazing period⁷ so grazing muzzles and strip grazing can effectively control intake⁵ when out at grass. If available, track systems can be useful to limit access to grazing, whilst encouraging increased activity. 

If grass access must be eliminated entirely, low NSC (<10% on a dry matter basis) preserved forage should be offered in portioned meals over 24 hours and horses can be turned out in all-weather pens. If elimination of grass has been required for a period, it is important to reintroduce access to grazing gradually with horses being monitored closely to prevent further complications.

 For horses needing to lose weight aim to provide 1.5% of their body weight in forage each day on a dry matter basis, this meets requirements for fibre intake without providing excess calories. For horses needing to gain condition, maximise conserved forageby feeding 2% of their bodyweight in forage.  Figure 3.0 outlines how much forage to feed each day depending on horse bodyweight, condition and forage type. 

Hay is often more suitable than haylage for horses with insulin dysregulation (ID) as it can be soaked prior to feeding to reduce the sugar content, aim to soak for 30 minutes – 1hr. Research has shown that soaking for up to 1 hour reduces the sugar content can reduce the sugar content to below target levels⁸.

For good doers, good quality straw can also be used to replace up to 30% of a horses daily forage allowance, straw is high in fibre but low in calories and sugar so can be useful when managing horses that need to lose weight. If implementing straw, introduce it gradually into the diet to allow the horse to adapt to the new fibre source and reduce the risk of digestive complications. 

Managing the good doer and over-conditioned PPID/EMS horses

When managing horses with EMS or PPID that are prone to being over conditioned, it can feel like a balancing act to make sure all their needs are met whilst managing insulin sensitivity and controlling calorie intake. 

These horses should be maintained within a healthy weight range by regulating calorie intake and increasing movement: any exercise is good to accelerate weight loss in obese animals and improve insulin sensitivity. With the exception of horses with ongoing laminitis which require veterinary supervision, a suitable exercise regime involves regular light work before building up intensity as fitness increases.

 Many horses needing a restricted diet can be greedy and will consume a hay net quickly, this can result in horses having unwanted prolonged periods without access to forage. Consider trickle feeding systems (small hole hay nets, hay balls, portion pacers) or split the forage ration into smaller more regular meals to avoid horses standing empty for prolonged periods. 

It is important for all horses to receive a source of vitamins and minerals in the diet, especially for those with restricted access to grazing as preserved forage is not as nutrient dense as fresh grass. For horses with ID and needing to maintain a healthy condition, opt for a feed balancer or a vitamin and mineral supplement, to provide key nutrients in a concentrated format. Pair this with a low calorie, oat straw-based chaff to slow intake and encourage chewing.

Feeding the lean or underweight PPID / EMS horse

To support condition extra calories can be added through feeds high in fibre and fat but controlled NSC. Horses with PPID may also suffer from muscle atrophy, in these cases look to supply quality protein through the diet. 

Look for balanced conditioning feeds with a high digestible energy content (DE) of >12 MJ/kg, high in oil/fat (>5%) and rich in quality protein (>12%) but that are low in starch & sugar. Adjunct straights such as unmolassed sugarbeet pulp and alfalfa chaff can also be added as low sugar, digestible fibre sources to add extra calories into the diet. 

 Keep meal sizes small, no more than 2kg should be in any one feed and aim to keep starch and sugar to a maximum of 1g per kg of body weight per meal. For example, for a 500kg horse, each meal should contain no more than 500g of starch and sugar combined. 

Some horses with PPID may struggle with inappetence, to tempt them to eat try offering smaller, more regular feeds, using soaked feeds or adding low-sugar herbs such as mint, garlic, cinnamon to the feed to help encourage eating up.