Digestible Energy in Horse Feed: What It Is & Why It Matters

What Is Digestible Energy in Horse Feed?

If you've ever read a feed label or spoken to an equine nutritionist, you've probably come across the term digestible energy — often abbreviated to DE. It's one of the most important numbers in horse nutrition, yet it's also one of the most misunderstood.

In simple terms, digestible energy is the amount of energy from feed that your horse can actually absorb and use. Not all the energy contained in a feedstuff is available to your horse. Some of it is lost in faeces, some in urine, and some as heat during digestion. Digestible energy accounts for the first and most significant of those losses — the energy lost in manure.

Here's the basic equation:

Digestible Energy (DE) = Gross Energy (GE) – Faecal Energy

Gross energy is the total energy locked within a feed. Faecal energy is the portion that passes through the horse undigested. What's left — the digestible energy — is what your horse actually gets to work with.

How Is Digestible Energy Measured?

DE is measured in megacalories (Mcal) or megajoules (MJ) per kilogram of feed. In the UK, Australia, and much of Europe, you'll usually see MJ. In the United States, Mcal is more common.

For context:

• 1 Mcal = 4.184 MJ
• A typical maintenance horse needs roughly 16–20 Mcal (or about 67–84 MJ) of DE per day, depending on body weight

DE values are determined through feeding trials where researchers measure exactly how much energy goes in (the feed) and how much comes out (the manure). The difference gives us the digestible energy value for that feedstuff.

Why Does Digestible Energy Matter?

Energy is the foundation of your horse's entire diet. Before you worry about protein, vitamins, or minerals, you need to get the energy balance right. Here's why DE matters so much.

1. It Determines Body Condition

The most visible effect of getting energy wrong is your horse's body condition. Too much digestible energy and your horse gains weight — potentially leading to obesity, laminitis, insulin resistance, and metabolic syndrome. Too little digestible energy and your horse loses weight, muscle, and condition.

A horse in moderate work needs significantly more DE than a horse standing in a paddock all day. If you feed both horses the same diet, one will be too fat and the other too thin.

2. It Fuels Performance

Whether your horse is a weekend trail companion or a competitive eventer, energy is what powers movement, muscle contraction, and recovery. Horses in hard work can require 50–100% more digestible energy than horses at maintenance. Getting this balance wrong can lead to:

• Poor performance and early fatigue
• Muscle wasting despite regular exercise
• Behavioural issues (either lethargy from too little energy or fizzy behaviour from the wrong energy source)

3. It Affects Digestive Health

The source of digestible energy matters just as much as the amount. Energy from fibre (forage) is digested slowly in the hindgut through microbial fermentation. Energy from starch and sugar (grains and concentrates) is digested rapidly in the small intestine. Overloading the small intestine with starch can cause undigested starch to spill into the hindgut, disrupting the microbial population and potentially triggering colic, hindgut acidosis, or laminitis.

This is why nutritionists always recommend that the majority of your horse's DE should come from forage.

4. It Supports Growth, Reproduction, and Lactation

Breeding mares, growing youngstock, and lactating mares all have dramatically higher DE requirements. A mare in late lactation may need up to 80% more energy than her maintenance requirement. Young, growing horses need carefully calibrated energy intake — too much can cause developmental orthopaedic disease, while too little stunts growth.

Digestible Energy Values of Common Horse Feeds

Understanding the DE content of different feeds helps you build a balanced diet. Here are approximate DE values for commonly fed ingredients:

Notice how vegetable oil stands out? Fat provides roughly 2.25 times more digestible energy per gram than carbohydrates, making it a calorie-dense option for horses that need extra energy without extra bulk or starch.

How to Calculate Your Horse's DE Requirements

Every horse is different, but the National Research Council (NRC) provides well-established guidelines for estimating DE requirements based on body weight and workload.

Step 1: Estimate Maintenance Requirements

The NRC formula for a mature horse at maintenance is:

DE (Mcal/day) = 0.0333 × Body Weight (kg)

So a 500 kg horse at maintenance needs approximately:

0.0333 × 500 = 16.65 Mcal/day (roughly 69.7 MJ/day)

Step 2: Add Energy for Work

Work increases DE requirements by a percentage above maintenance:

• Light work (1–3 hours/week): +20%
• Moderate work (3–5 hours/week): +40%
• Heavy work (intense training, competition): +60–80%
• Very heavy work (racing, elite endurance): +80–100%

For our 500 kg horse in moderate work:

16.65 × 1.4 = 23.3 Mcal/day (roughly 97.5 MJ/day)

Step 3: Adjust for Individual Factors

These formulas provide starting points. You'll need to adjust based on:

• Breed and metabolism: Some breeds are "easy keepers" (native ponies, cobs) while others are "hard keepers" (Thoroughbreds)
• Age: Older horses may have reduced digestive efficiency
• Climate: Cold weather increases energy demands for thermoregulation
• Body condition score: If your horse needs to gain or lose weight, you'll need to adjust DE accordingly
• Temperament: Nervous or highly strung horses may burn more calories

If you're unsure whether your horse's current diet is meeting their energy needs, analysing your horse's diet is an excellent starting point. It takes the guesswork out of nutrition and shows you exactly where the gaps are.

DE vs. Other Energy Systems

You might occasionally encounter other energy measurement systems. Here's how they compare:

Gross Energy (GE)

The total energy in a feed, measured by burning it in a laboratory. Not particularly useful because it doesn't account for what the horse can actually digest.

Metabolisable Energy (ME)

This goes a step further than DE by also subtracting energy lost in urine and gases. While more precise in theory, ME is harder to measure in horses and is used less commonly. DE remains the standard in equine nutrition.

Net Energy (NE)

The most precise measure — it accounts for energy lost as heat during metabolism (the "heat increment" of feeding). NE is commonly used in cattle nutrition but is rarely applied in equine science because the data is limited and DE has proven sufficiently accurate for practical diet formulation.

For horse owners, DE is the gold standard and the system used by the NRC, most feed companies, and equine nutritionists worldwide.

Common Mistakes With Digestible Energy

Overfeeding Energy to Horses in Light Work

This is perhaps the most common mistake. Many leisure horses and ponies are fed concentrates designed for horses in moderate to hard work. The result is excess energy, weight gain, and increased risk of metabolic problems. If your horse is in light work or at rest, good quality forage may provide all the DE they need — often with a simple balancer pellet for vitamins and minerals.

Ignoring Forage in Energy Calculations

Forage typically provides 50–100% of a horse's daily DE intake, yet many owners only think about energy when choosing a concentrate feed. Always calculate the energy contribution of hay, haylage, or pasture first, then top up with concentrates only if needed.

Choosing the Wrong Energy Source

A racehorse and a dressage horse may need similar total DE, but the ideal sources differ. High-starch feeds provide quick-release energy suited to intense, short-duration work. Fibre and fat provide slow-release energy better suited to endurance and steadier disciplines. Matching the energy source to the type of work is just as important as getting the total right.

Not Adjusting for Seasonal Changes

Horses' energy needs change with the seasons. Winter cold increases maintenance energy needs, while spring grass can flood a horse with excess DE. Many cases of spring laminitis occur because owners don't account for the dramatic increase in energy (and sugar) that comes with lush pasture growth.

Practical Tips for Managing Your Horse's Digestible Energy Intake

1. Weigh your forage. You can't manage what you don't measure. Use a hanging scale to weigh hay nets and know exactly how much your horse is eating.

1. Get your hay tested. DE values for hay can vary enormously depending on maturity at cutting, grass species, and storage. A hay analysis gives you actual numbers rather than estimates.

1. Feed by weight, not volume. A scoop of oats weighs very differently to a scoop of pellets. Always weigh concentrate feeds.

1. Use body condition scoring. Regularly score your horse on a 1–9 scale (Henneke system). This is the simplest and most reliable way to tell whether your DE provision is on track.

1. Adjust gradually. When changing energy intake — whether increasing for work or decreasing for a rest period — make changes over 7–14 days to protect gut health.

1. Consider fat supplementation. If your horse needs more energy but is already receiving significant grain, adding vegetable oil (up to 100 ml/100 kg body weight per day) can increase DE without increasing starch load.

The Bottom Line

Digestible energy is the single most important nutritional value in your horse's diet. It determines body condition, fuels performance, and — when managed poorly — can be at the root of many common health problems. Understanding what DE is, how much your horse needs, and where it should come from puts you in a strong position to feed your horse well.

The key takeaway? Start with forage, calculate the energy it provides, and only add concentrates if there's a genuine shortfall. Match the energy source to the type and intensity of work, and monitor body condition regularly to fine-tune your approach.

Good nutrition doesn't have to be complicated — but it does have to be intentional.