Starch and Sugar in Horse Feed: What You Need to Know

Why Starch and Sugar in Horse Feed Matter

If you've ever read a feed label and felt confused by terms like "starch," "sugar," "NSC," or "WSC," you're not alone. Understanding starch and sugar in horse feed is one of the most important — and most misunderstood — aspects of equine nutrition.

These two nutrients are the horse's primary sources of quick energy, but when fed in excess, they can trigger serious health problems including laminitis, metabolic syndrome, gastric ulcers, and dramatic behavioural changes. Getting the balance right is essential for every horse owner.

In this article, we'll break down exactly what starch and sugar are, how your horse digests them, what levels are safe, and how to manage your horse's intake for optimal health.

What Are Starch and Sugar?

Before diving into feeding strategies, let's clarify what we're actually talking about.

Sugar (Water-Soluble Carbohydrates — WSC)

Sugar in the context of horse nutrition usually refers to water-soluble carbohydrates (WSC). These include simple sugars like glucose, fructose, and sucrose, as well as fructans — a type of storage carbohydrate found abundantly in cool-season grasses.

Sugar is naturally present in:

• Pasture grass (levels vary hugely with season, weather, and time of day)
• Hay and haylage
• Many commercial feeds, particularly those containing molasses
• Treats like carrots and apples (in moderate amounts)

Starch

Starch is a complex carbohydrate made up of long chains of glucose molecules. It's the primary energy storage molecule in cereal grains. Feeds high in starch include:

• Oats
• Barley
• Maize (corn)
• Wheat
• Commercial mixes and pellets containing cereal grains

Starch provides a concentrated source of energy, which is why grain-based feeds have traditionally been used for working horses. However, the equine digestive system has a limited capacity to handle large amounts of starch at once.

NSC — Non-Structural Carbohydrates

You'll often see the term NSC (Non-Structural Carbohydrates) on feed analyses. NSC is simply the combined total of starch and WSC:

> NSC = Starch + WSC (sugar)

This figure gives you the best overall picture of how much rapidly available carbohydrate your horse is consuming. It's the number that matters most when managing metabolic conditions.

How Your Horse Digests Starch and Sugar

Understanding digestion is key to understanding why too much starch and sugar can be dangerous.

The Small Intestine — Where Starch Should Be Digested

In an ideal scenario, starch is broken down by enzymes in the small intestine into glucose, which is then absorbed into the bloodstream. The horse's body releases insulin to shuttle that glucose into cells for energy.

However, the horse's small intestine has a limited capacity for starch digestion. Research suggests that the upper safe limit is approximately 1–2 grams of starch per kilogram of body weight per meal. For a 500 kg horse, that translates to roughly 500g–1 kg of starch per meal — which is easier to exceed than you might think.

The Hindgut — Where Problems Begin

When starch intake exceeds the small intestine's capacity, the undigested starch passes through to the hindgut (caecum and large colon). This is where the horse's fibre-fermenting bacteria live.

Starch that arrives in the hindgut is rapidly fermented by lactic acid-producing bacteria, which:

• Causes a sharp drop in hindgut pH (hindgut acidosis)
• Kills beneficial fibre-fermenting bacteria
• Releases endotoxins into the bloodstream
• Can trigger laminitis, colic, and loose droppings

This is why large grain meals are one of the leading dietary causes of laminitis and digestive disturbance.

Sugar Digestion

Simple sugars are absorbed quickly in the small intestine and cause a rapid rise in blood glucose and insulin. Fructans, however, are not broken down by mammalian enzymes. Like excess starch, they pass to the hindgut where they're fermented — and can cause the same acidotic cascade.

This is why lush spring and autumn pasture, which is rich in fructans, is a well-known laminitis trigger.

How Much Starch and Sugar Is Safe?

Safe levels depend on your individual horse's health status, workload, and metabolic condition.

General Guidelines

Per-Meal Starch Limits

Regardless of your horse's health status, it's wise to keep starch intake below 1 g per kg bodyweight per meal. For a 500 kg horse, that's no more than 500 g of starch per meal.

To put this in perspective:

• 1 kg of oats contains roughly 400–450 g of starch
• 1 kg of barley contains roughly 550–600 g of starch
• 1 kg of maize contains roughly 650–700 g of starch

So even a seemingly modest grain feed can push your horse past safe starch limits if you're not careful.

Signs Your Horse May Be Getting Too Much Starch or Sugar

Horses receiving excessive starch and sugar often show a range of symptoms. Watch for:

• Excitability and "fizzy" behaviour — blood sugar spikes can cause erratic energy levels
• Weight gain and fat pads — especially cresty neck, fat over the shoulders, or a large belly
• Loose droppings or diarrhoea — a sign of hindgut disturbance
• Laminitis or foot sensitivity — particularly after turnout on lush pasture
• Recurrent gastric ulcers — high-starch diets increase stomach acid production
• Muscle tying-up — some forms of tying-up (like PSSM) are directly linked to starch and sugar intake

If you notice any of these, it's time to review and adjust your feeding programme.

How to Manage Starch and Sugar in Your Horse's Diet

1. Know What's in Your Feed

The first step is understanding exactly what your horse is eating. Check feed labels for starch and sugar content, and ask your forage supplier for a hay analysis. Hay can vary enormously — from 5% NSC to over 25% — and you won't know without testing.

For a thorough overview, try analysing your horse's complete diet to see the total starch and sugar intake across all feeds, forage, and supplements combined.

2. Choose Low-Starch Feed Options

If your horse doesn't need the energy provided by cereal grains, switch to fibre-and-oil-based feeds. Good low-starch options include:

• Unmolassed sugar beet pulp — high in digestible fibre, very low in starch
• Soya hulls — another excellent low-starch fibre source
• Oil supplements (such as linseed or rice bran oil) — provide slow-release energy without starch
• Commercial low-starch feeds — many manufacturers now produce feeds with less than 10% starch specifically designed for laminitics and metabolically challenged horses
• Chaff and chopped fibre — ensure they're unmolassed

3. Manage Pasture Access

Grass can be the single biggest source of sugar in your horse's diet — and it's the one most owners underestimate.

• Fructan levels peak during sunny days with cold nights (common in spring and autumn)
• Morning grass (before 10am) tends to be lower in sugar than afternoon grass
• Stressed grass (drought, frost, overgrazing) can accumulate very high sugar levels
• Use a grazing muzzle or strip grazing to limit intake
• Consider a track system for horses that need severely restricted grazing

4. Feed Little and Often

If your horse does need some starch-based feed for energy (such as a horse in hard work), split the daily ration into three or more small meals rather than two large ones. This keeps each meal within the small intestine's digestion capacity and minimises the risk of hindgut overflow.

5. Prioritise Forage

Forage (hay, haylage, or pasture) should always form the foundation of your horse's diet — a minimum of 1.5–2% of bodyweight per day in dry matter. A forage-first approach naturally reduces the need for high-starch concentrates.

If your hay is high in NSC and your horse is metabolically sensitive, you can soak hay for 30–60 minutes in cold water to leach out some of the soluble sugars. Soaking typically reduces WSC by 20–40%, though results vary.

6. Consider the Whole Diet

It's easy to focus on one feed and miss the bigger picture. Your horse's total daily starch and sugar intake comes from the combination of:

• Pasture
• Hay or haylage
• Hard feed or concentrates
• Supplements (some contain hidden sugars)
• Treats

All of these must be accounted for to get an accurate picture.

Special Considerations

Horses with Equine Metabolic Syndrome (EMS)

Horses with EMS have impaired insulin regulation. Even moderate amounts of starch and sugar can trigger dangerously high insulin levels, which directly damage the laminae in the hooves. These horses need strict NSC restriction — typically below 10% of total diet — and careful pasture management.

Horses with PPID (Cushing's Disease)

Many horses with PPID also develop insulin dysregulation, particularly in autumn. The same low-NSC dietary principles apply. Work closely with your vet to monitor ACTH and insulin levels alongside dietary management.

Horses with PSSM (Polysaccharide Storage Myopathy)

PSSM Type 1 horses have a genetic mutation that causes them to store excessive glycogen in their muscles. A low-starch, high-fat diet is essential — typically less than 10% NSC with fat providing 15–20% of calories.

Performance Horses

Horses in intense work (racing, eventing, endurance) do have higher energy demands. However, modern nutrition has shown that much of this energy can be provided through digestible fibre and oil rather than relying heavily on cereal grains. Many top-level performance horses now thrive on lower-starch diets, with the added benefits of calmer behaviour and better digestive health.

Frequently Asked Questions

Is sugar in horse feed always bad?

No. Sugar is a natural component of forage and provides readily available energy. The problem arises when total sugar and starch intake exceeds your horse's ability to digest and metabolise it safely. For healthy horses in work, moderate sugar levels are perfectly fine.

Are oats better than barley or maize?

Oats have a slightly lower starch content than barley or maize and the starch in oats is more digestible in the small intestine (meaning less reaches the hindgut). If you must feed cereal grains, oats are generally the safest option.

Does soaking hay remove all the sugar?

No. Soaking reduces WSC by approximately 20–40%, but it doesn't eliminate it entirely. For horses that need very low NSC forage, you may need to source specifically tested low-sugar hay. Steaming hay does not significantly reduce sugar content.

Can I just cut out all starch and sugar?

You don't need to eliminate starch and sugar entirely — that's neither practical nor necessary for most horses. The goal is to keep intake within safe limits for your horse's individual needs.

Key Takeaways

• Starch and sugar are natural energy sources, but the horse's digestive system has limited capacity to handle them safely
• Excess starch reaching the hindgut causes acidosis, which can trigger laminitis, colic, and digestive upset
• Keep total diet NSC below 10–12% for metabolically sensitive horses; below 20% for healthy horses
• Limit starch to no more than 1 g per kg bodyweight per meal
• Pasture grass can be the biggest hidden source of sugar — manage it carefully
• Use fibre and oil as alternative energy sources where possible
• Always assess the whole diet, not just individual feeds

Understanding starch and sugar in horse feed empowers you to make smarter feeding decisions. Whether your horse is a laminitis-prone native pony or a hard-working sport horse, getting these levels right is one of the most impactful things you can do for their long-term health and wellbeing.