Evidence-based feeding strategies for horses with EMS, insulin dysregulation and laminitis risk, and why underfeeding metabolic horses can sometimes do more harm than good.
There is a growing trend in some areas of equine management to recommend prolonged periods of hay restriction combined with feeding as little as 1 to 1.5% of body weight for horses with obesity, insulin dysregulation and Equine Metabolic Syndrome (EMS).
It is meant to improve metabolic health. It often does the opposite. Severe restriction can worsen the very insulin resistance it is trying to fix, and in the most vulnerable horses it can be dangerous.
At first glance, the logic appears straightforward. Excess body fat is associated with altered insulin regulation and increased laminitis risk in susceptible horses. If obesity contributes to metabolic dysfunction, then reducing calorie intake aggressively, and underfeeding metabolic horses, should theoretically improve metabolic health more quickly.
However, physiology is rarely that simple.
Reducing excess body fat and inducing prolonged negative energy balance are not metabolically equivalent states. Weight loss achieved through gradual reduction in body condition while maintaining adequate nutrient intake is very different from severe restriction that triggers adaptive responses designed to preserve survival during perceived starvation.
Scientific Insight
Weight loss and starvation response are not the same thing. Gradual fat loss while maintaining adequate nutrition is metabolically very different from severe calorie restriction that activates adaptive survival mechanisms.
These distinctions matter because the body’s response to prolonged underfeeding of metabolic horses and ponies may include altered insulin sensitivity, increased mobilisation of stored fat reserves and broader metabolic adaptations that do not necessarily align with improved metabolic function.
Even relatively short periods of fasting have been shown to alter insulin-related responses in horses [1], while prolonged negative energy balance is recognised as a risk factor for excessive fat mobilisation and hyperlipemia in susceptible equids [3].
This does not suggest that calorie control has no role in the management of metabolic disease. Nor does it imply overweight horses should be overfed. Rather, it raises an important question:
At what point does calorie restriction stop supporting metabolic improvement and begin triggering physiological responses capable of working against that goal?
Understanding where that balance lies is important because successful management depends not only on reducing excess body fat but also on maintaining adequate nutrition and preserving metabolic stability throughout the process.
Quick Summary
Effective management depends on balancing weight reduction with adequate nutritional intake
Severe calorie restriction does not automatically improve insulin sensitivity
Even short fasting periods can alter insulin responses in horses[1]
Prolonged negative energy balance increases reliance on stored fat reserves[2][3]
Susceptible equids may be at increased risk of hyperlipemia under severe restriction[3]
Main takeaway: Weight loss and starvation are not the same thing. Good management reduces excess body fat while keeping nutrition adequate and metabolic stability intact. It does not simply feed less.
Why Calorie Restriction Seems Logical for Metabolic Horses
The widespread use of restrictive feeding strategies in horses with obesity, insulin dysregulation and recurrent laminitis did not develop without reason. There are sound physiological arguments supporting reduction of excess body fat and control of dietary sugar intake, and many horses improve when these factors are managed appropriately.
Adipose tissue is not simply an energy reserve. Fat tissue functions as an active endocrine organ involved in hormonal signalling, inflammation and regulation of insulin sensitivity. Horses carrying excessive body condition are more likely to develop insulin dysregulation, and prolonged elevations in circulating insulin are strongly associated with increased risk of endocrinopathic laminitis in susceptible animals.
For these reasons, weight reduction through underfeeding metabolic horses frequently becomes an important component of management programmes for metabolic horses.
Similarly, reducing dietary exposure to non-structural carbohydrates (NSC), particularly sugars and starches capable of stimulating exaggerated insulin responses, remains an established principle in the nutritional management of insulin dysregulated horses. Together, these concepts have contributed to common recommendations such as restricting forage intake, prolonged hay soaking, severe grazing restriction and feeding lower-calorie diets.
Many horses improve under these strategies.
However, an important distinction often receives less attention:
Reducing calorie intake sufficiently to support gradual fat loss is not necessarily equivalent to inducing prolonged negative energy balance through severe restriction.
The difference is not simply one of degree. As restriction and underfeeding metabolic horses becomes more severe, the body increasingly shifts from supporting normal metabolic function toward activating adaptive mechanisms intended to preserve survival.
Under these circumstances, physiological responses may begin prioritising energy conservation and maintenance of essential functions rather than improving metabolic efficiency.
This distinction matters because the body’s response to prolonged restriction does not necessarily align with the assumption that progressively lower calorie intake will always produce progressively better metabolic outcomes.
The important question is not whether weight loss matters, but whether progressively greater restriction continues to support the same metabolic goals. Understanding that distinction requires looking more closely at what happens physiologically during severe calorie restriction.
What Happens Physiologically During Severe Calorie Restriction?
The horse is adapted to survive periods of reduced food availability. When calorie intake falls substantially below requirements, the body does not simply continue losing weight in a linear way. Instead, physiological priorities begin to shift towards preserving energy supply for essential functions. This distinction matters because the body’s response to gradual fat loss achieved with adequate nutrition is very different from its response to prolonged negative energy balance.
Gradual fat loss vs severe restriction
| Gradual fat loss | Severe restriction |
|---|---|
| Supports steady weight reduction | May activate adaptive starvation responses |
| Maintains adequate nutrient intake | Can compromise protein, mineral and vitamin intake |
| Supports metabolic stability | May increase reliance on stored fat mobilisation |
| Allows monitoring and gradual adjustment | May increase metabolic stress in vulnerable equids |
One of the more counterintuitive adaptations involves insulin responsiveness. Under conditions of feed deprivation, tissues such as skeletal muscle may become less responsive to insulin, helping preserve circulating glucose for organs with higher energy demands. This response, often described as adaptive insulin resistance, represents a survival mechanism rather than a primary disease process. Even relatively short fasting periods have been shown to alter insulin-related responses in horses [1], suggesting feed deprivation itself is not metabolically neutral.
At the same time, reduced calorie intake increases reliance on stored fat reserves. Mobilising fat for energy is a normal response to insufficient intake.
However, continued oxidation of mobilised fat depends upon metabolic intermediates generated from glucose and amino acid metabolism. Even with muscle breakdown, these intermediates may become limited during prolonged severe restriction, impairing continued fat metabolism and contributing to fat accumulation within the liver [2][3].
These changes become particularly relevant in ponies, donkeys and miniature horses, which appear more vulnerable to the development of hyperlipemia during significant negative energy balance [3].
Hyperlipemia is characterised by markedly elevated circulating triglycerides and abnormal fat accumulation within organs, including the liver. The condition can progress rapidly and is often fatal in severe cases [3].
These physiological responses help explain why gradual reduction in body condition and prolonged severe restriction should not automatically be treated as equivalent strategies.
When severe restriction may be risky
Some horses and equids are more vulnerable to the effects of prolonged negative energy balance, particularly where fat mobilisation, insulin dysregulation or medication use are already concerns.
Can Fasting Alter Insulin Responses in Horses?
One of the assumptions often underlying severe calorie restriction is that reducing feed intake should automatically improve insulin sensitivity. However, evidence from fasting studies in horses suggests the relationship may be more complex.
Bertin and colleagues investigated the effect of fasting duration on several commonly used insulin-related tests in horses [1]. The researchers found that fasting influenced measurements including blood glucose concentration, insulin concentration and responses to tests used to assess insulin dynamics.
In practical terms, even relatively short periods without feed reduced insulin responsiveness, indicating altered insulin sensitivity under conditions of feed deprivation [1].
These findings are important because they demonstrate that fasting itself is not metabolically neutral.
However, careful interpretation is essential. The study did not demonstrate that short-term fasting causes Equine Metabolic Syndrome, nor did it establish that fasting alone induces chronic pathological insulin dysregulation comparable to naturally occurring metabolic disease. Instead, the findings suggest feed deprivation can influence insulin handling and alter responses in ways that may complicate assumptions regarding calorie restriction and metabolic improvement [1].
This distinction matters because an adaptive response to reduced intake is not necessarily equivalent to chronic metabolic disease. The body may alter insulin responsiveness under conditions of perceived starvation as part of a broader strategy designed to preserve energy availability for essential tissues.
Nevertheless, the findings raise an important practical question:
If even relatively short fasting periods alter insulin-related responses, could prolonged or severe calorie restriction intended to improve metabolic health sometimes produce physiological adaptations that work against that goal?
More research is needed to determine how different degrees and durations of restriction influence long-term insulin sensitivity in horses. However, the available evidence suggests aggressive restriction strategies deserve careful scrutiny, particularly in metabolically vulnerable animals [1][3].
These findings also reinforce a broader principle that runs throughout the management of metabolic horses:
Restriction alone is not automatically evidence of better metabolic management. The response of the individual horse remains important.
Hay Restriction, Soaking and Unintended Consequences
Restricting forage intake and soaking hay are common strategies used when managing obesity, insulin dysregulation and laminitis risk. The rationale is understandable. Reducing intake of non-structural carbohydrates, particularly water-soluble sugars, may help lower insulin responses in susceptible horses, while reducing overall calorie intake may support weight loss where excess body condition contributes to metabolic dysfunction.
However, the effects of aggressive restriction and prolonged soaking are more complex than simply:
Common assumption vs reality
Common assumption
Less sugar equals a better outcome
Reality
Research investigating hay soaking has shown that soaking duration may alter not only carbohydrate content, but also energy value, protein availability, amino acid composition, minerals and trace elements [4]. The extent of these changes varies depending on forage type, soaking duration and environmental conditions, meaning the nutritional consequences of soaking are not always predictable [4].
This is important because longer soaking does not necessarily translate into proportionally greater metabolic benefit. More soaking is not automatically better soaking. Prolonged soaking may reduce nutrients while producing variable effects on sugars [4].
This does not mean hay soaking should be avoided altogether.
Rather, it suggests soaking protocols should be applied strategically, with consideration given to both potential benefits and unintended nutritional consequences.
Maximum soaking time
Where soaking is necessary, Dr Kellon gives a clear limit, and longer is not better.
Maximum
Maximum
Beyond these limits, soaking tends to strip additional nutrients without a matching reduction in sugar, and bacterial growth accelerates, a particular concern in warm weather.[4][5]
Another factor receiving increasing attention is bacterial growth. Research evaluating bacterial ecology associated with soaked hay demonstrated that soaking alters microbial populations, with prolonged soaking linked to increased bacterial proliferation under some conditions [5]. Environmental temperature may further influence these changes, making extended soaking periods potentially more problematic during warmer conditions [5].
The clinical significance of altered bacterial populations remains an area requiring further investigation. However, the findings reinforce an important principle:
Hay soaking is not a metabolically neutral intervention.
It changes forage composition in multiple ways, some potentially beneficial and others requiring consideration.
For horses requiring lower sugar forage, soaking may still have an important role. However, management decisions are ideally guided by forage analysis rather than assumptions regarding sugar content or nutritional adequacy. Understanding the actual ESC, starch, digestible energy and nutrient profile of forage provides a stronger basis for deciding whether soaking is necessary, how extensive soaking should be and whether nutritional losses require compensation elsewhere in the ration.
In practical terms, Dr Kellon’s guidance is specific: feed only hay that tests under 10% combined ESC and starch, while recognising that individual sensitivity varies. It is a defined figure, not a guess, which is exactly why forage analysis matters. Without it, there is no way to know whether a given hay already sits under that threshold or whether soaking is needed to bring it there.
The objective should not simply be feeding the lowest-calorie forage possible.
The objective is to support gradual fat loss while maintaining adequate nutritional intake and minimising unnecessary metabolic stress.
How Much Should You Feed a Metabolic Horse?
For owners managing obesity, insulin dysregulation or recurrent laminitis, one practical question tends to arise quickly:
How much forage is enough to support weight loss without creating unintended metabolic stress?
Unfortunately, there is no single answer suitable for every horse.
Requirements vary according to body condition, degree of insulin dysregulation, activity level, age, breed, forage composition, concurrent disease and medication use. A feeding strategy appropriate for one horse may be inadequate or unnecessarily restrictive for another.
This variability matters because metabolic management is not simply about reducing calories as far as possible. The objective is to support a gradual reduction in excess body fat while maintaining adequate nutrient intake and preserving metabolic stability throughout the process.
A practical rule of thumb used in management of metabolic horses is feeding approximately 1.5% of current body weight as forage dry matter, or 2% of ideal body weight, whichever amount is greater.
Severe restriction is not automatically a safer restriction.
Practical feeding example
Take a horse weighing 600 kg with an ideal body weight of 500 kg. The two calculations give:
Current body weight
9 kg
1.5% of 600 kg, forage dry matter per day
10 kg
2% of 500 kg, forage dry matter per day
Feed the higher of the two. The rule of thumb is 1.5% of current body weight or 2% of ideal, whichever is greater, so here the 10 kg figure is the more appropriate starting point.
The aim is not to create the largest calorie deficit possible.
The aim is to encourage sustainable fat loss while avoiding prolonged negative energy balance severe enough to trigger adaptive starvation responses.
Another important consideration is that forage quantity alone does not determine energy intake. Ten kilograms of one hay may provide substantially different digestible energy compared with ten kilograms of another. Two horses consuming apparently similar amounts of forage may therefore receive very different calorie intakes.
This is one reason forage analysis becomes particularly valuable in the management of metabolic horses.
Understanding:
- Digestible energy (DE)
- ESC
- Starch
- Protein
- Mineral composition
provides a stronger basis for nutritional decisions than relying solely on forage weight.
As a secondary check, feed approximately 0.0304 Mcal/kg body weight using the Equine DE from the hay analysis. However, this should always be interpreted within the context of the individual horse, forage quality and clinical response.
Without forage analysis, management decisions often rely heavily on assumptions.
Those assumptions may contribute to:
- Excessive restriction
- Inadequate nutrient intake
- Persistent obesity despite reduced feeding
- Unnecessary soaking
- Difficulty understanding why progress has stalled
For metabolically vulnerable horses, feeding progressively less is not always synonymous with improving metabolic health.
In some circumstances, increasingly severe restrictions may create physiological conditions capable of working against the intended goal.
Successful management, therefore, depends less on pursuing the lowest possible calorie intake and more on balancing gradual fat reduction with adequate nutrition, measured forage composition and ongoing assessment of the individual horse’s response.
The challenge is not simply helping the horse lose weight. The challenge is helping the horse lose weight without compromising metabolic stability in the process.
Interactive tool
The protein cost of a restricted diet.
Restricting forage — and substituting straw for weight loss — cuts calories, but it quietly cuts protein too. Adjust the ration below and see how far it falls below what your horse actually needs.
Your horse’s or pony’s bodyweight.
Sets the protein requirement.
Total forage per day, as % of bodyweight (as fed / on the scale). Severe restriction starts at 1.5% and below.
Share of that forage replaced with straw. ~30% is a common weight-loss recommendation.
UK average from Forageplus analysis: 7.3% (dry matter basis).
UK average from Forageplus analysis: 2.9% (dry matter basis).
UK average from Forageplus analysis: 81%. The rest is moisture, so protein is reduced to match.
Typical ~88% (straw is drier than hay). Enter your own if tested.
These use UK-average protein and dry matter levels. Real forage varies widely — a full nutritional analysis tells you what your own hay and straw actually contain.
Hay only
7.5 kg hay
Your ration
with straw
Methodology. Minimum crude protein based on NRC requirements, scaled to bodyweight; optimum = 150% of minimum, a practical target for muscle maintenance, topline, ageing and recovery. Protein delivered = as-fed forage weight × dry matter % × crude protein % (crude protein is reported on a dry matter basis, so it is adjusted for moisture). Test your forage to replace the UK averages with your own figures.
Test your forage →Special Considerations: Horses Receiving Ertugliflozin or Other Flozin Medications
The increasing use of sodium-glucose co-transporter-2 (SGLT2) inhibitors, including ertugliflozin, in horses with severe insulin dysregulation has introduced additional considerations regarding nutritional management and calorie restriction.
These medications work by increasing urinary glucose excretion, helping reduce circulating glucose and insulin concentrations. While this can provide important benefits in carefully managed cases, it also changes the metabolic context in which weight loss strategies occur.
For horses receiving ertugliflozin or similar medications, severe calorie restriction warrants particular caution. Dr Kellon’s original recommendation is that calorie restriction in horses receiving flozin medications may, in some circumstances, become rapidly fatal. This concern reflects the potential consequences of excessive negative energy balance occurring alongside altered glucose handling.
When nutritional intake becomes inadequate, the body increasingly relies upon the mobilisation of stored energy reserves. In horses already experiencing altered glucose handling through medication, excessive negative energy balance may create physiological circumstances capable of increasing metabolic instability. This concern becomes especially relevant where rapid weight loss or aggressive restriction strategies are pursued alongside medical management.
The practical implication is important:
Strategies intended to maximise weight loss through severe restriction should not automatically be assumed to represent the safest approach in horses receiving flozin therapy.
Management should instead prioritise maintaining adequate forage intake, monitoring body condition and rate of weight loss carefully, and avoiding prolonged restriction severe enough to induce significant negative energy balance.
As with all metabolic management, individual response matters.
The appropriate balance between supporting weight reduction and maintaining adequate nutritional intake will depend upon the horse’s clinical status, insulin regulation, forage composition and overall management plan.
Because recommendations regarding optimal feeding strategies during flozin therapy continue to evolve, management should ideally be undertaken with veterinary supervision and informed by current evidence where available.
For owners, the broader message remains consistent with the rest of this discussion:
More aggressive restriction is not automatically safer restriction.
In some circumstances, particularly where medication alters glucose handling, severe calorie deficits may require greater caution rather than less.
Practical caution
On a flozin medication, severe calorie restriction can be rapidly fatal. This is Dr Kellon’s original and explicit warning, and it is the reason this group needs particular care.
Horses receiving ertugliflozin or other SGLT2 inhibitors are already handling glucose differently because of the medication. Adding a large energy deficit on top of that can tip a vulnerable horse into a dangerous state very quickly.
For these horses, management should prioritise maintaining adequate nutritional intake and avoiding excessive negative energy balance, ideally under veterinary supervision.
An Evidence-Based Feeding Strategy for Metabolic Horses
Managing horses with obesity, insulin dysregulation, Equine Metabolic Syndrome (EMS) or recurrent laminitis risk is rarely about pursuing the most aggressive restriction possible. Successful long-term management depends on balancing gradual weight reduction with adequate nutrient intake, while supporting metabolic stability throughout the process.
The challenge is not simply reducing calorie intake. The challenge is reducing excess body fat while preserving metabolic stability.
In practical terms, this means management strategies are more likely to succeed when based on measurement and ongoing assessment rather than assumptions.
1. Start With Forage Analysis Rather Than Guesswork
Two hays that appear similar visually may differ substantially in digestible energy, sugar, starch, protein and mineral content. Without analysis, feeding decisions often rely on estimates, making it difficult to determine whether restriction is necessary, whether soaking is justified or whether nutritional adequacy is being maintained.
For metabolically vulnerable horses, understanding the actual nutritional composition of forage provides a stronger foundation for management than progressively increasing restriction in response to persistent obesity or insulin dysregulation.
2. Reduce Sugar and Starch Exposure Where Necessary
For horses with insulin dysregulation or laminitis susceptibility, reducing dietary non-structural carbohydrates often remains an important component of management.
Where lower sugar forage is required:
- Select suitable forage where possible
- Use soaking strategically rather than assuming longer soaking is automatically better [4]
- Consider potential nutrient losses associated with prolonged soaking [4]
- Recognise bacterial changes associated with extended soaking durations [5]
Restriction strategies should aim to improve metabolic safety while preserving overall nutritional quality.
3. Prioritise Gradual Fat Loss Rather Than Rapid Weight Reduction
Weight reduction can improve metabolic outcomes in many horses. However, severe or prolonged restriction may increase reliance on adaptive responses associated with negative energy balance, including altered insulin responsiveness and increased fat mobilisation [1][2].
The aim should therefore be a sustainable reduction in excess body condition rather than pursuing the fastest possible rate of weight loss.
Gradual improvement is often more physiologically appropriate than aggressive restriction.
4. Maintain Adequate Nutritional Intake During Weight Loss
Reducing calories does not remove nutritional requirements.
Protein, amino acids, vitamins, minerals and sufficient energy to support normal physiological processes remain important throughout weight management. Feeding programmes should therefore consider forage quality, nutrient density and overall ration adequacy rather than focusing solely on calorie reduction.
Weight loss strategies become increasingly difficult to justify if nutritional sufficiency is compromised in the process.
5. Exercise Particular Caution in Vulnerable Horses
Ponies, miniature horses, donkeys and horses with severe insulin dysregulation may be more vulnerable to complications associated with prolonged negative energy balance, including excessive fat mobilisation and hyperlipemia [3].
Similarly, horses receiving medications affecting glucose handling may require additional caution regarding aggressive restriction.
These situations reinforce an important principle:
The most restrictive feeding strategy is not automatically the safest strategy.
6. Monitor Response and Adjust Accordingly
No single feeding percentage, calorie target or management protocol is universally appropriate.
Successful metabolic management requires ongoing assessment of:
- Body condition score
- Weight trends
- Clinical signs
- Laminitis risk
- Insulin status where relevant
- Response to dietary changes
Management plans should evolve according to the horse’s response rather than remaining fixed.
Practical Summary
For many metabolic horses, an evidence-based approach involves:
Analysing forage before making major dietary changes
Reducing sugar exposure where clinically appropriate
Supporting gradual and sustainable fat loss
Maintaining adequate nutrient intake during weight reduction
Avoiding unnecessarily severe restriction
Monitoring progress and adapting management over time
The bottom line is simple. Do not starve a metabolic horse. Test the forage, lower sugar and starch where the analysis calls for it, keep nutrition adequate, and let the weight come off gradually. That is what turns a metabolic horse around. Severe restriction does not.
Our Evidence-Based Approach
At Forageplus, we believe effective management of metabolic horses begins with understanding what the forage actually contains.
Forage analysis provides measurable insight into:
- Digestible energy
- Sugar and starch content
- Protein levels
- Mineral balance
- Nutritional adequacy during weight management
Rather than relying on increasingly severe restriction, our approach prioritises informed feeding decisions based on measured nutrient supply and the individual horse’s requirements.
The goal is not simply to feed less.
The goal is to feed appropriately while supporting long-term metabolic health.
Unsure what to feed a metabolic horse?
Every horse responds differently to restriction, grazing and forage. Get a bespoke feeding plan built around your horse, its workload, your forage analysis and its metabolic needs, from one of our equine nutritionists.
Get feeding advice →Evidence-based nutritional support · Forage-focused advice · Individual recommendations
References
Bertin, F.R., Taylor, S.D., Bianco, A.W., & Sojka-Kritchevsky, J.E. (2016). The effect of fasting duration on baseline blood glucose concentration, blood insulin concentration, glucose/insulin ratio, oral sugar test, and insulin response test results in horses. Journal of Veterinary Internal Medicine, 30(5), 1726-1731. View source
Koffler, M., & Kisch, E.S. (1996). Starvation diet and very-low-calorie diets may induce insulin resistance and overt diabetes mellitus. Journal of Diabetes and Its Complications, 10(2), 109-112. View source
McKenzie, H.C. III. (2011). Equine hyperlipidemias. Veterinary Clinics of North America: Equine Practice, 27(1), 59-72. View source
Bochnia, M., Pietsch, C., Wensch-Dorendorf, M., Greef, M., & Zeyner, A. (2021). Effect of hay soaking duration on metabolizable energy, total and prececal digestible crude protein and amino acids, non-starch carbohydrates, macronutrients and trace elements. Journal of Equine Veterinary Science, 101, 103452. View source
Moore-Colyer, M.J.S., Longland, A., Harris, P., Zeef, L., & Crosthwaite, S. (2020). Mapping the bacterial ecology on the phyllosphere of dry and soaked hay for horses. PLoS ONE, 15(1), e0227151. View source
