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

Why Starch and Sugar Matter in Your Horse's Diet

If you've ever wondered why your horse turns into a fire-breathing dragon after a grain feed, or why your good doer seems to pile on weight from thin air, the answer often lies in two words: starch and sugar.

Starch and sugar are the two main components of what nutritionists call non-structural carbohydrates (NSC). They're a natural part of nearly every feed and forage your horse eats, but when levels get too high — or the wrong type of horse consumes too much — the consequences can range from mild behavioural issues to life-threatening conditions like laminitis.

Understanding starch and sugar in horse feed is one of the most important things you can do as a horse owner. This guide will break it all down in plain English so you can make confident, informed decisions about what goes in your horse's feed bin.

What Are Starch and Sugar, Exactly?

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

Sugar (Water-Soluble Carbohydrates — WSC)

Sugars are simple carbohydrates that dissolve in water. In horse nutrition, the term water-soluble carbohydrates (WSC) covers a range of simple sugars (like glucose and fructose) and short-chain fructans. These are found naturally in grass, hay, and many commercial feeds.

Sugars are rapidly absorbed in the small intestine, causing a relatively quick rise in blood glucose levels. Think of sugar as the "fast fuel" — it provides quick energy but can cause hormonal and metabolic spikes when consumed in excess.

Starch

Starch is a more complex carbohydrate made up of long chains of glucose molecules. It's found in high concentrations in cereal grains like oats, barley, maize (corn), and wheat.

Your horse's small intestine can digest starch using enzymes, breaking it down into glucose for energy. However, the horse's small intestine has a limited capacity to digest starch — and this is where problems begin.

Non-Structural Carbohydrates (NSC)

When you see NSC on a feed label or in nutritional advice, it typically refers to:

NSC = WSC (sugar) + Starch

This combined figure is the number most nutritionists focus on when assessing how "safe" a feed or forage is for metabolically sensitive horses.

How Your Horse Digests Starch and Sugar

Understanding digestion is key to understanding why too much starch and sugar causes problems.

The Small Intestine: The Ideal Pathway

When your horse eats a moderate amount of starch or sugar, enzymes in the small intestine break it down into glucose. This glucose is absorbed through the gut wall and into the bloodstream, where it can be used for energy or stored as glycogen in muscles and the liver.

This is the normal, healthy pathway. The problem is capacity.

The Hindgut: When Things Go Wrong

The horse's small intestine can only process a limited amount of starch at a time — research suggests roughly 1 to 2 grams of starch per kilogram of bodyweight per meal. For a 500kg horse, that's about 500g to 1kg of starch per feed.

When starch intake exceeds this threshold, the undigested starch passes through to the hindgut (the cecum and large colon). The hindgut is designed to ferment fibre, not starch. When starch arrives there, it's rapidly fermented by bacteria that produce lactic acid, which:

• Drops the pH of the hindgut (acidosis)
• Kills off beneficial fibre-fermenting bacteria
• Damages the gut lining, potentially allowing toxins into the bloodstream
• Can trigger laminitis, colic, and other serious conditions

This process is called hindgut acidosis, and it's one of the most common nutritional causes of health problems in horses.

Where Do Starch and Sugar Hide in Your Horse's Diet?

You might be surprised by how many sources of starch and sugar are in a typical horse's daily intake.

Cereal Grains

These are the biggest culprits for high starch levels:

A single scoop of a grain-based mix can contain a significant starch load. Always check the guaranteed analysis on your feed bag.

Grass and Hay

This is the one that catches most people off guard. Grass can contain anywhere from 5% to over 30% NSC, depending on:

• Time of day — sugar levels peak in the afternoon after photosynthesis
• Season — spring and autumn grass tends to be highest in sugar
• Temperature — cool nights followed by sunny days cause sugar to accumulate
• Stress — drought-stressed or frost-stressed grass can have very high sugar levels
• Species — ryegrass and some improved pasture species are particularly high in sugar

Hay retains most of the sugar content it had when it was cut, though some sugar is lost during the curing process. Soaking hay for 30–60 minutes in cold water can reduce WSC by roughly 20–40%, though results vary.

Commercial Feeds

Many commercial compound feeds, mixes, and pellets contain cereal grains as a base. Molasses is also commonly added as a binder and palatability enhancer, contributing additional sugar. Always read the label and look for the declared starch and sugar percentages.

Treats and Supplements

Apples, carrots, mints, and many commercial horse treats contain sugar. While the amounts from occasional treats are usually small, they can add up — especially for a horse on a restricted diet.

Which Horses Need Low Starch and Sugar Diets?

While every horse benefits from a sensible approach to starch and sugar, certain horses are particularly vulnerable to excess NSC.

Horses and Ponies Prone to Laminitis

Laminitis is the number one reason owners need to understand NSC. Excess sugar and starch — whether from lush grass or a grain-heavy bucket feed — can trigger laminitic episodes through insulin dysregulation and/or hindgut acidosis pathways. Most laminitis experts recommend keeping total dietary NSC below 10–12% for at-risk horses.

Horses with Equine Metabolic Syndrome (EMS)

EMS horses have abnormal insulin responses. When they consume sugar and starch, their blood insulin levels spike far higher than normal, and this hyperinsulinaemia can directly damage the laminae in the hooves. These horses need strict NSC management.

Horses with PPID (Cushing's Disease)

Horses with Pituitary Pars Intermedia Dysfunction (PPID or Cushing's) often develop insulin dysregulation as a secondary problem. Managing starch and sugar is a critical part of their care plan.

Horses with Gastric Ulcers

High-starch diets have been associated with an increased risk of gastric ulcers. Starch fermentation in the stomach produces volatile fatty acids that can damage the unprotected squamous lining of the stomach.

Horses with Behavioural Issues

Some horses become excitable, spooky, or difficult to manage on high-starch diets. Reducing cereal grain intake and switching to fibre-and-oil-based feeds often produces a noticeable calming effect.

Horses Prone to Tying-Up (PSSM/RER)

Horses with polysaccharide storage myopathy (PSSM) or recurrent exertional rhabdomyolysis (RER) benefit significantly from low-starch, high-fat diets. For PSSM horses, dietary starch and sugar should typically be kept below 10% of total intake.

Practical Tips for Managing Starch and Sugar

Now for the part you can actually act on. Here's how to take control of NSC levels in your horse's diet.

1. Know Your Numbers

You can't manage what you don't measure. Check the starch and sugar percentages on every feed bag. For hay, consider getting it tested — a forage analysis will tell you the exact WSC and starch levels. If you're unsure whether your horse's overall diet is balanced and safe, analysing your horse's diet is an excellent first step to getting clarity.

2. Choose Low-NSC Feeds

Look for feeds marketed as "low starch" or "low sugar" — but always verify by reading the actual declared analysis. A good low-NSC feed will typically have:

• Starch below 10% (ideally below 5% for very sensitive horses)
• Combined sugar + starch (NSC) below 12–15%
• A fibre-and-oil base rather than a cereal grain base

Feeds based on sugar beet pulp (unmolassed), soya hulls, alfalfa, and added oil are generally much lower in NSC than traditional grain mixes.

3. Feed Little and Often

If you do need to feed starch-containing feeds (for example, to fuel hard work), split the ration into multiple small meals. Remember the rule: no more than 1–2g of starch per kg bodyweight per meal. For a 500kg horse getting a feed with 20% starch content, that means no more than about 2.5–5kg of that feed per meal — but ideally much less.

4. Manage Grazing Carefully

For laminitis-prone or metabolically challenged horses:

• Use a grazing muzzle to reduce grass intake by up to 80%
• Turn out in the early morning when grass sugar levels are lowest
• Avoid grazing on sunny afternoons, especially in spring and autumn
• Consider strip grazing or using a bare paddock with supplementary soaked hay
• Be extra cautious after cold nights followed by sunny mornings

5. Soak Your Hay

Soaking hay in cold water for 30–60 minutes (or warm water for 15–30 minutes) leaches out a proportion of the water-soluble sugars. It won't remove starch, and results vary depending on the hay, but it's a useful tool for reducing overall NSC. Always drain the soaking water away — don't let your horse drink it.

Steaming hay does not significantly reduce sugar levels, though it is excellent for reducing dust and mould spores.

6. Use Oil for Extra Calories

If your horse needs more energy but you want to keep starch low, adding vegetable oil is a fantastic option. Oil provides roughly 2.5 times more energy than the same weight of oats, with zero starch and zero sugar. Start slowly (50–100ml per day) and build up over 2–3 weeks to allow the digestive system to adapt. Most horses can tolerate up to 100ml per 100kg bodyweight per day.

7. Consider Fibre-Based Alternatives

Super fibres like unmolassed sugar beet pulp and soya hulls are digested in the hindgut through normal fibre fermentation but release more energy than traditional hay. They're an excellent way to add condition and calories without the starch spike.

Reading Feed Labels: What to Look For

When you pick up a bag of feed, look for:

• Starch % — the lower the better for most horses
• Sugar % — sometimes listed as "sugars" or as part of WSC
• NSC or combined starch + sugar — some manufacturers declare this directly
• Fibre % — higher fibre generally means lower starch
• Oil % — a higher oil content often indicates a low-starch, energy-dense feed

If the label doesn't declare starch and sugar separately, contact the manufacturer — any reputable feed company will provide this information.

Common Myths About Starch and Sugar

"Oats are the safest grain for horses"

Oats are more digestible in the small intestine than barley or maize, which is true. But they still contain 40–45% starch. A large feed of oats can still overload the small intestine and cause hindgut problems. "Safer" doesn't mean "safe in any quantity."

"My horse needs grain for energy"

For the vast majority of horses in light to moderate work, quality forage plus a balancer pellet provides more than enough energy. Cereal grains are only necessary for horses in sustained, high-intensity work — and even then, the trend in equine nutrition is moving toward fibre-and-oil-based energy sources.

"Sugar-free feeds have no sugar"

No feed or forage is truly sugar-free. Even hay contains sugar. "Low sugar" is a more accurate and honest description. Be wary of marketing claims and always check the numbers.

The Bottom Line

Starch and sugar are not inherently evil — they're natural components of your horse's diet and a legitimate energy source in appropriate amounts. The key is understanding how much your horse is consuming, whether they need it, and whether their body can handle it.

For most leisure horses, good-quality forage, a feed balancer, and careful grazing management will provide everything they need — with far less starch and sugar than a traditional grain-based diet.

If your horse has a metabolic condition, a history of laminitis, or unexplained behavioural changes, taking a close look at the starch and sugar content of their entire diet — from grass to bucket feed to treats — could be the single most impactful change you make.

Your horse's health starts in the feed room. Understanding what's actually in the bucket is the first step to getting it right.