Insulin resistance in horses: a complete guide for 2026

Your horse has looked increasingly rounded for several months, despite apparently receiving the same feed. You have reduced hard feed and give the same amount of hay, yet a firm crest appears on the neck, fat develops around the tailhead, or there is a worrying history of sore feet after spring. This is one of those moments when you feel frustrated: you care for your horse, yet the problem keeps growing.

This is often how a conversation about metabolic disorders begins. Not with dramatic signs, but with a sense that your horse gains weight on fresh air, responds less well to exercise or has episodes that cannot readily be explained by feeding by eye.

Insulin resistance: a silent problem in your stable

Your horse looks well in the morning. They eat eagerly, go into the paddock and sometimes even work normally. Yet you increasingly feel that something is going wrong. Their shape changes, fat accumulates in characteristic places, they fill out faster than they should after the grazing season, and their old feeding routine stops working.

This is why insulin resistance can be so insidious. For a long time, your horse does not look seriously ill. Instead, there are small signs easily attributed to breed, age, little exercise or good grass. In practice, this is often when you hear reassuring comments, even though your horse's body is already struggling with excess energy and an excessive insulin response after meals.

The problem often forms part of a wider picture of metabolic disorders. In many horses, it occurs alongside regional fat deposits and an increased risk of laminitis. It is particularly common in ponies, good doers and animals kept on rich pasture, but is not limited to these groups. I also see it in leisure and sport horses that do not look typically metabolic at first glance.

You usually start suspecting something in quite specific situations:

• your horse gains weight despite an apparently sensible ration,
• a firmer crest develops on the neck,
• fat accumulates around the tailhead or behind the shoulder,
• your horse looks worse after grazing than after a period of regular work,
• there is a history of laminitis or unexplained foot soreness.

This matters because insulin resistance does not always simply mean an overweight horse. Sometimes the problem runs deeper. Your horse may not yet look dramatically different, but their metabolism is already working less efficiently. For you, it is rather like driving with a warning light that has not stopped the engine yet but clearly says action is needed.

The good news is that you can manage this effectively and systematically. You need a plan: appropriate diagnosis, restricted sugar and starch, suitable fibre, safe weight loss, daily exercise and feeds and supplements that make sense for a horse with metabolic issues. Below, I will explain this step by step, including specific options available in Poland, such as Spillers feeds and Equine America supplements, and why combining them can help rather than simply being another trial change.

What insulin resistance is and how it works

Insulin is a hormone that helps cells take glucose from the blood. The simplest way to picture it is this: insulin is the key and the cell is the lock. When everything works properly, the key fits, the lock opens and glucose goes where it is needed.

With insulin resistance, this mechanism becomes less effective. The key still exists, but the lock responds reluctantly. The body tries to force a solution. The pancreas releases more and more insulin to push glucose into the cells.

What happens in your horse's body

Initially, you do not usually see the insulin itself. You see the effects. Your horse develops fat easily, copes less well with a pasture-based diet and responds more readily to excess starch or sugar. In practice, the main problem is not simply rich feeding, but a large insulin release after meals.

Polish nutritional and veterinary sources identify a diet rich in non-structural carbohydrates, or NSC as the main environmental stimulus for the development and persistence of insulin resistance in horses, particularly when cereals and feeds that rapidly raise blood glucose and insulin form a large proportion. When managing horses with metabolic issues, recommendations include restricting or eliminating hard feeds rich in simple sugars and starch, avoiding molasses and cereals, and building the ration around fibre and oils, as described in the material on insulin resistance in horses and practical feeding.

Insulin resistance is not the same as diabetes

This often causes confusion. You hear insulin and immediately think of diabetes. Yet these terms are not interchangeable. A horse can have insulin disorders without the features of classic diabetes. Avoid attaching a label yourself based on one laboratory result or because your horse drinks more than usual.

Briefly:

An important distinction: with insulin resistance, weight gain is a concern, but above all we worry about the link with laminitis.

This is why dietary changes are part of protecting health, rather than simply a fitness plan.

Early signs and warning signals

You usually notice changes in your horse's body before seeing test results. That is helpful, provided you know what to look for. The most typical finding is regional fat deposits, rather than necessarily general obesity. Your horse may have a prominent fatty crest on the neck and soft or firm fat pads behind the shoulder, around the tailhead or near the sheath or udder.

Not every horse with metabolic problems looks barrel-shaped. Sometimes it is a sport horse maintaining their figure but carrying disproportionate fat on the neck. Sometimes it is a senior horse that has lost muscle while still depositing fat in characteristic places.

What you can notice yourself

Regularly run your hand over your horse's body and compare what you feel with previous weeks. Particularly important areas are:

• The neck and fatty crest. A firm, swollen-looking neck is a sign you should not dismiss.
• The tailhead. Fat accumulation here can be very characteristic.
• A changed response to pasture. After a few days on grass, your horse looks heavier, moves less comfortably or becomes more sensitive.
• A history of laminitis or sore feet. Even if the episode was long ago and seemed isolated.

Subtler signs that are easy to miss

Some horses show more than changes in shape. Owners also describe:

• Less energy for work or, conversely, irritability and discomfort.
• Fluctuating performance without a clear cause.
• Difficulty losing weight despite a restricted ration.
• Recurring problems that do not seem connected and therefore distract attention from metabolism.

If your horse has had laminitis, has a fatty neck and copes poorly with rich pasture, treat this as a red light rather than a coincidence.

A short weekly checklist is a useful habit:

This daily awareness does not replace testing. However, it often determines whether you seek help early enough.

Diagnosing insulin resistance in your horse

In practice, diagnosis rarely rests on a single result. It is more like assessing the whole picture. Your horse has signs, a feeding history, a workload and sometimes previous laminitis, while laboratory tests form one part of the puzzle.

This frustrates many owners. You want a simple answer after one blood sample. Insulin resistance usually does not work that way, because your horse's body is not a light switch. It is more like a lock and key responding better or worse depending on stress, season, diet and current health.

Where the vet usually starts

The starting point is a detailed history and clinical examination. The vet asks not only what your horse eats, but what daily life looks like. Have they had pasture access, become less willing to move, developed more sensitive feet or gained weight despite an apparently moderate ration?

Blood tests only become meaningful against this background. Insulin and glucose concentrations are most commonly assessed. If the picture remains unclear, the vet may suggest dynamic tests, which assess how the body responds to a given stimulus. This provides far more information than a single number on a printout.

Some horses require a broader view. PPID can also cause signs resembling IR, particularly in older animals. Good diagnosis therefore asks what exactly lies behind the result, rather than stopping at whether insulin was too high.

How to interpret an insulin result

An insulin result needs careful interpretation. It is not a verdict on its own. It is a signal to consider alongside glucose, clinical signs, body condition and sampling conditions.

The most common mistake is receiving a result, seeing a number outside the reference range and assuming everything is clear. Yet the same horse may produce a different result on another day, after different feeding or at a different stress level. The vet therefore considers trends and context, rather than one box on the report.

Briefly, the result only makes sense when it fits the rest of the picture.

A practical rule: ask your vet not only about insulin itself, but whether the result fits your horse's signs, glucose, laminitis history and age.

What a sensible approach looks like

The safest and clearest plan is:

1. History and clinical examination
   The vet assesses body shape, fat tissue, hooves, feeding history, response to pasture and previous painful episodes.

2. Basic tests
   Measuring insulin and glucose provides an initial reference point.

3. Additional tests if needed
   When signs are clear but results give no definite answer, dynamic tests may be necessary.

4. Distinguishing other diseases
   Ruling out or confirming PPID is particularly important in older horses.

5. Turning diagnosis into an action plan
   This is where practical help begins. You need to establish how to feed your horse, whether and how much they can exercise, how to protect the hooves and how to monitor progress.

The last point matters greatly. Good diagnosis does not end with naming the problem. It should lead to decisions you can put into practice in the stable immediately. That is why the rest of this article moves from testing to practice: a safe diet, choosing specific Spillers feeds and Equine America supplements, and combining them into a plan that makes sense for a horse with IR.

Managing the diet of a horse with insulin resistance

You return to the stable, look at your horse and think: they no longer get oats, so things should be better. Yet the fatty crest is still firm, weight is not falling and laminitis remains a worry. This is common. With insulin resistance, the problem usually involves the entire combination of hay, grass, extras and feeding methods, rather than one bag of feed.

In practice, diet has one main aim: limiting amounts of sugar and starch that trigger large insulin releases. The easiest comparison is a lock and key. Insulin tries to open the cells, but the body responds less effectively, so the pancreas makes more. The more often we add fuel through sugar-rich or starchy feeds and rich grass, the harder it becomes to interrupt this mechanism.

What really harms and what helps

Three things usually cause the most problems: cereal-based feeds, products containing molasses and uncontrolled pasture access. You may focus only on hard feed while your horse gets the largest sugar intake from grass or hay of unknown composition.

A fibre-based ration helps instead. Good hay, a steady eating pace, no molasses and sensible vitamin and mineral provision. This diet does not give the body a sudden surge. It provides steadier metabolic conditions, which matters for a horse struggling with insulin.

If you have doubts about the hay, consider soaking it. This is no universal magic solution, but it can be a practical way to reduce some readily available sugars. Be consistent and maintain hygiene, because soaked hay spoils faster.

Building a safe foundation for the ration

Start with a simple plan you can implement immediately in the stable, without confusion or starving your horse.

• Base the ration on hay. This is usually the foundation of feeding a horse with IR. If your horse eats very quickly, use a slow-feeding net.
• Assess the hay rather than guessing. If you do not know its quality, treat it cautiously. Soaking helps in some cases.
• Remove cereals, molasses and sweet extras. Leisure mixes, bread, large amounts of carrots and flavoured treats can undermine a well-designed diet.
• Be cautious with grass. For many horses with insulin resistance, pasture is a more difficult part of the diet than going without hard feed.
• Add a fibre component if needed. Chaff without molasses helps extend eating time and provides a safer way to add meal volume.
• Balance the ration with a balancer or a suitable vitamin and mineral supplement. A horse with IR still needs protein, minerals and vitamins. They simply should not come with a large sugar and starch load.

This is an important point. Many owners cut calories after diagnosis but leave the diet poorly balanced. Your horse eats less, yet still does not receive what their muscles, hooves and hormonal system need.

Thinking practically, day by day

A good diet for a horse with IR should answer three questions: what forms the foundation, how you correct deficiencies and how you limit hidden sugars. This is why a ready-made plan based on specific products makes sense. Not because a bag of feed treats insulin resistance, but because it makes it easier to build a ration without accidental mistakes.

In Polish conditions, a sensible approach is hay as the foundation, followed by a fibre feed without molasses, then a balancer or supplement supplying nutrients without adding cereals. This is safer, easier to monitor and simpler to maintain for months, rather than just the week after diagnosis.

Removing oats alone rarely solves the problem. The whole ration matters. A horse with insulin resistance needs predictable, fibre-based, low-sugar feeding that remains nutritionally complete. This provides the best starting point for choosing specific Spillers feeds and Equine America supplements.

Recommended feeds and supplements for horses with IR

After diagnosis, many owners fall into extremes. Oats, mix and treats disappear, leaving only hay and considerable uncertainty about whether your horse receives everything needed. A calm, structured plan works better for insulin resistance: first choose a safe ration foundation, then supply nutrients, and only finally consider supplements for a specific problem.

It is like building a diet in three layers. The first should avoid provoking large insulin releases. The second should provide vitamins, minerals and protein often lacking after hard feed is reduced. The third should support your horse where there is a real clinical problem, such as hooves after laminitis or ongoing discomfort.

Choosing products for a safe, nutritionally complete ration

In practice, the easiest way to assess a product is by its role in the ration, rather than claims on the bag.

Combining Spillers HAPPY HOOF Molasses Free and Spillers Lite & Lean Balancer makes sense in this approach. The first helps create safe, fibrous meal volume. The second supplies what hay and a small amount of supporting feed cannot provide alone.

This distinction matters. Chaff does not replace a balancer, and a balancer does not replace a fibre foundation. One supplies structure and chewing time; the other provides concentrated nutrients without large amounts of sugar and starch.

Why this combination makes sense for a horse with IR

Spillers HAPPY HOOF Molasses Free is useful when you want to give your horse something bulky and metabolically safer than a typical cereal- or molasses-based mix. It often solves a practical daily problem: your horse needs something in the manger, but that something should not increase dietary risk.

Spillers Lite & Lean Balancer is useful for good doers, horses on restricted energy rations or those unable to receive conventional hard feed. It works as a precise addition to the ration. It adds few calories but helps supply what the body still needs: amino acids, trace minerals and vitamins.

This is where many owners lose their way. You see improvement because your horse receives less sugar, but after a few weeks other problems begin: a weaker topline, poorer hoof quality, a dull coat and less willingness to work. Often this is not IR being difficult, but the result of a ration that is low in sugar yet still poorly balanced.

Equine America supplements. When they may be justified

A supplement should not be the first step. First organise hay, the fibre foundation and ration balance. Only then assess whether your horse needs additional support.

In the Equine America range, consider supplements in terms of a specific purpose:

• Lamigard TRT Solution may be considered for horses with a history of laminitis when you want hoof and metabolic support as part of a broader nutritional and veterinary plan.
• Turmeric Xtra is more often suited to horses with ongoing discomfort or signs of strain alongside metabolic problems.

These are not simply products for insulin resistance. They do not replace a well-designed ration. They may, however, support your horse in a particular situation when chosen sensibly and given a clear place in the overall management plan.

A practical approach for three common situations

A leisure horse that gains weight easily
A simple combination often works well: hay as the foundation, a little chaff without molasses and a balancer instead of conventional hard feed. This makes weight control easier and reduces the risk of accidentally supplying too much energy.

A horse after a laminitis episode
Consistency and predictability matter here. The ration should be very simple, fibre-based and continually monitored, with supplements chosen alongside the vet and the farrier responsible for your horse.

A working horse with metabolic issues
Your horse still needs fuel for work, but it must come from a more safely formulated ration. The aim is not to add cereals because they work, but to choose fibre, a balancer and any additions to maintain condition without overloading insulin regulation.

The most practical question is therefore not which feed is best for IR, but what role this product should play in your horse's ration. An honest answer makes it much easier to combine Spillers feeds and Equine America supplements into a safe, nutritionally complete diet you can maintain every day.

Prevention, exercise and long-term monitoring

Imagine an ordinary week in the stable. Your horse looks well, eats eagerly and shows no obvious pain, yet after a few quieter days the neck becomes firmer again, the belly grows and you wonder whether everything is still heading in the right direction. This is often what long-term management of insulin resistance looks like. The outcome depends on daily routine rather than one bag of feed or one supplement.

Exercise as part of treatment

For a horse with IR, exercise regularly opens the door for glucose in the muscles. Working muscles use energy more efficiently, so the body does not need such a large insulin response as in an inactive horse. Sensibly chosen daily activity is therefore part of treatment and preventing recurrence.

The main rule is simple: exercise must be regular and safe for the hooves. If your horse has had laminitis, is sore or noticeably stiff, first stabilise their condition with your vet and hoof care professional. Only then increase the workload.

In practice, the best plan is one you can maintain for months, rather than a week. For one horse, this means brisk in-hand walking and groundwork; for another, gentle riding, hacking or light lunging. Consistency matters. Horses with metabolic issues usually respond better to frequent moderate exercise than occasional strenuous training.

What to monitor daily

A long-term plan need not be complicated. It must be consistent.

• Check condition by touch and sight. Fat on the neck, behind the shoulder and around the tailhead often returns before it becomes apparent in phone photographs.
• Record every significant ration detail. Different hay, longer grazing, a new batch of chaff or an extra handful can change more than you expect.
• Observe exercise tolerance. If your horse tires sooner, becomes stiffer or turns reluctantly, the plan needs adjusting.
• Check hooves and gait. Even a subtle movement change deserves attention in a horse with IR.
• Repeat tests as advised by your vet. Follow-up testing should answer one question: is the current plan really working?

A simple system of photographs and measurements also works well. Take side and rear photographs every 2 to 4 weeks, ideally in the same place. Record chest circumference using a weight tape. When you see your horse daily, it is easy to get used to changes. Notes help reveal what memory misses.

A horse with IR does best when each day is predictable. Similar exercise, a similar ration and similar monitoring.

This also has practical implications for feeding. If your horse maintains weight well on hay, a suitable Spillers balancer and safe chaff, there is no reason to change the plan without cause. If energy drops, muscle quality declines or vitamin and mineral provision becomes difficult, you can then add a product with a specific function instead of guessing. The same applies to Equine America supplements. They make sense when they address a defined problem and fit the whole ration, rather than as a just-in-case extra.

If you look at your horse and feel something is changing, it is usually worth responding immediately. With insulin resistance, early small adjustments are much simpler than firefighting later.

To turn these principles into a specific ration for your horse, explore VETfactory. You will find Spillers feeds, Equine America supplements and equine nutrition products, and can choose according to composition, purpose and the needs of your horse with metabolic problems.