Protein in Horse Feed: How Much Does Your Horse Need?

Protein is one of the most misunderstood nutrients in equine nutrition. Some horse owners worry about feeding too much, fearing it will make their horse "hot" or cause kidney damage. Others don't give it a second thought. The truth, as usual, lies somewhere in between — and getting it right matters more than most people realise.

In this article, we'll break down exactly how much protein your horse needs, what protein actually does in the body, which amino acids matter most, and how to tell if your horse's diet is falling short.

What Does Protein Do for Horses?

Protein isn't just about building muscle. It plays a fundamental role in virtually every biological process in your horse's body, including:

• Muscle development and repair — the most well-known function
• Hoof growth — hooves are made primarily of keratin, a structural protein
• Coat and skin health — hair is also protein-based
• Immune function — antibodies are proteins
• Enzyme and hormone production — essential for digestion and metabolic regulation
• Red blood cell production — haemoglobin contains protein

Without adequate protein, horses can lose topline condition, develop poor hoof quality, show a dull coat, heal slowly from injuries, and have compromised immune systems. Young, growing horses are particularly vulnerable to protein deficiency.

Understanding Crude Protein on Feed Labels

When you look at a feed bag, you'll see a value listed as crude protein (CP). This is the total nitrogen content of the feed multiplied by 6.25 — a standard conversion factor. It gives you a rough estimate of total protein content, but it doesn't tell you everything.

Here's what crude protein doesn't tell you:

• The quality of the protein — not all protein sources are created equal
• The amino acid profile — which specific building blocks are present
• Digestibility — how much of that protein your horse can actually absorb and use

A feed with 14% crude protein from high-quality sources like soybean meal will deliver far more usable protein than a feed with 14% crude protein from poor-quality, heat-damaged forage. This is why looking beyond the crude protein number is essential.

Amino Acids: The Real Story Behind Protein

Proteins are made up of chains of amino acids. There are roughly 20 amino acids that matter in equine nutrition, and several of these are classified as essential — meaning the horse cannot manufacture them internally and must obtain them from the diet.

The most critical essential amino acids for horses are:

Lysine

Lysine is considered the first limiting amino acid in most equine diets. This means it's typically the amino acid that runs out first, putting a ceiling on how effectively the horse can use all the other protein in the diet. If lysine is deficient, it doesn't matter how much total crude protein you feed — the horse simply cannot use it efficiently.

Good sources of lysine include soybean meal, full-fat soybeans, lucerne (alfalfa), and specifically formulated amino acid supplements.

Threonine

Threonine is the second limiting amino acid and plays a key role in gut health, immune function, and the production of mucin — the protective lining of the digestive tract.

Methionine

Methionine is the third limiting amino acid and is particularly important for hoof and coat quality, as it's a sulphur-containing amino acid that contributes to the structural integrity of keratin.

When assessing your horse's protein intake, focusing on these three amino acids — especially lysine — is far more valuable than fixating on the crude protein percentage alone.

How Much Protein Does Your Horse Actually Need?

Protein requirements vary significantly depending on age, workload, reproductive status, and body condition. The following guidelines are based on recommendations from the National Research Council (NRC, 2007), which remains the gold standard reference for equine nutrition.

Adult Horses at Maintenance

A mature horse at maintenance (light to no work) requires approximately 1.26 g of crude protein per kg of body weight per day. For a 500 kg horse, that works out to roughly 630 g of crude protein per day.

Most horses at maintenance can meet this requirement through good-quality forage alone. A horse eating 2% of its body weight in average grass hay (around 8-10% CP) will typically consume 800-1000 g of crude protein — more than enough.

Lysine requirement at maintenance: approximately 27 g per day for a 500 kg horse.

Horses in Work

Contrary to popular belief, exercise increases protein requirements only moderately. The bigger increase is in energy (calorie) requirements. However, horses in moderate to heavy work do need more protein for muscle repair and red blood cell turnover.

Most horses in moderate work will meet their protein needs through a combination of quality forage and a commercial feed fed at the manufacturer's recommended rate.

Growing Horses

Young, growing horses have the highest protein requirements relative to their body weight. Foals, weanlings, and yearlings are building new tissue rapidly, and inadequate protein — particularly lysine — can result in stunted growth, poor muscling, and developmental issues.

• Weanlings (6 months): approximately 14.5% crude protein in the total diet, with at least 0.65% lysine
• Yearlings (12 months): approximately 12.5% crude protein, with at least 0.55% lysine
• Two-year-olds: approximately 11% crude protein, with at least 0.45% lysine

Lucerne hay or haylage is particularly valuable for young horses because of its higher protein content and excellent lysine levels compared to grass forage.

Broodmares

Pregnant mares have increased protein needs, but mainly during the last trimester when foetal growth accelerates dramatically. A mare in late pregnancy needs approximately 900-1000 g of crude protein per day.

Lactating mares have even higher demands — they may need 1,400-1,500 g of crude protein per day during peak lactation (the first three months after foaling). This makes lactation one of the most nutritionally demanding stages of a horse's life.

Senior Horses

Older horses often have reduced digestive efficiency and may struggle to extract protein from forage, particularly if they have dental issues that compromise chewing. Research suggests that horses over 20 years of age may benefit from diets containing 12-14% crude protein, with attention paid to protein quality and digestibility.

Feeds designed for senior horses typically use highly digestible protein sources like soybean meal and beet pulp to compensate for reduced gut efficiency.

Common Myths About Protein in Horse Feed

"Too Much Protein Makes Horses Hot"

This is one of the most persistent myths in horse management. There is no scientific evidence that dietary protein causes excitable behaviour in horses. The "hot" behaviour that owners sometimes observe when feeding high-protein feeds like lucerne is more likely related to the calorie content of the feed, or simply the horse's individual temperament. Protein and energy are different things.

"Excess Protein Damages the Kidneys"

In healthy horses, excess protein is simply broken down by the liver, and the nitrogen waste product (urea) is excreted through the kidneys in urine. A healthy horse can handle moderate protein excesses without kidney damage. You may notice a stronger ammonia smell in the stable — that's the urea being excreted — but this is not a sign of kidney disease.

That said, there's no benefit to massively over-feeding protein. Excess protein is an inefficient and expensive energy source, and the increased ammonia in bedding can irritate airways — a genuine concern, especially for horses prone to respiratory issues.

"All Protein Sources Are the Same"

As we discussed earlier, protein quality varies enormously. The amino acid profile and digestibility of soybean meal are far superior to that of cereal grains, for example. When choosing feeds, don't just compare crude protein percentages — consider the source of that protein.

Signs Your Horse May Need More Protein

Keep an eye out for these potential indicators of protein deficiency:

• Loss of topline — muscle wasting along the back, neck, and hindquarters
• Poor hoof quality — slow growth, crumbling, or weak hoof wall
• Dull, rough coat — coat fails to shed properly or lacks shine
• Slow wound healing — cuts and injuries take longer to resolve
• Reduced performance — lack of stamina or slow recovery after exercise
• Poor growth in young horses — failure to thrive or lagging behind peers

If you notice these signs, the first step is to assess the overall diet rather than simply adding a high-protein supplement. Often, the issue is forage quality or the horse not receiving enough feed overall.

How to Get Your Horse's Protein Right

Step 1: Start with Forage

Forage should be the foundation of every horse's diet, and it's also the primary source of protein for most horses. Get your hay or haylage tested so you know its actual crude protein content — this can vary dramatically from 5% to 18% or more depending on the type of forage and when it was cut.

Step 2: Choose the Right Hard Feed

If your horse's forage doesn't meet protein requirements — common with mature, late-cut grass hay — then a concentrate feed or balancer can fill the gap. Feed balancers are particularly useful because they provide quality protein (including lysine) along with vitamins and minerals without excessive calories.

Step 3: Analyse the Whole Diet

The only way to truly know if your horse's protein intake is adequate is to look at the complete diet — forage plus any concentrates, supplements, and additional feeds. Analysing your horse's diet with a tool like MyEquibalance allows you to see exactly where the nutritional gaps are and whether protein, amino acids, and other nutrients are being met.

Step 4: Adjust Seasonally

Remember that forage quality changes throughout the year. Spring and early summer grass is typically higher in protein than winter hay. Your horse's diet may need seasonal adjustments to maintain consistent nutrition.

Best Protein Sources for Horses

If you need to increase protein in your horse's diet, here are some of the best options:

Avoid relying on cereal grains (oats, barley, maize) as your primary protein source. While they do contain some protein (8-12%), the amino acid profile is poor and lysine content is low.

The Bottom Line

Protein is an essential nutrient that your horse cannot do without, but more isn't always better. The key is to provide the right amount of quality protein with adequate essential amino acids — particularly lysine — matched to your horse's age, workload, and life stage.

For most adult horses in light to moderate work, good-quality forage combined with a well-formulated feed or balancer will meet protein requirements comfortably. Young, growing horses, lactating mares, and seniors may need more targeted attention.

Rather than guessing, take the time to assess your horse's complete diet. Understanding what's actually going into your horse each day is the single most effective step you can take toward optimal nutrition and long-term health.