Protein provides the amino acid building blocks your horse needs for muscle development and repair, hoof growth, coat quality, immune function, and the production of enzymes and hormones that regulate nearly every bodily process. Horses break dietary protein down into individual amino acids and reassemble them into the specific proteins their body needs. The quality of protein matters as much as the quantity — lysine is the first limiting amino acid in most equine diets, meaning it runs out before the others and becomes the bottleneck for protein synthesis. Threonine and methionine are typically the second and third limiting amino acids. A horse eating adequate total protein but deficient in lysine will not be able to build muscle efficiently, regardless of how much extra protein is provided. This is why alfalfa hay and soybean meal are valued in equine diets — they provide lysine-rich protein. Unlike some nutrients, excess protein is not stored; it is broken down and the nitrogen is excreted as urea through the kidneys and in urine, which is why high-protein diets produce strong-smelling, ammonia-heavy urine in stalls.
A 500kg horse at maintenance needs about 630 grams of crude protein per day — roughly the weight of a large loaf of bread. This is easily met by 10 kilograms of average-quality grass hay (8 to 10 percent protein). Horses in moderate work need about 800 grams, and growing yearlings or lactating mares may need 900 to 1,100 grams. Adding 1 to 2 kilograms of alfalfa hay to the daily ration is a simple way to boost both protein quantity and lysine quality.
26.63% of daily nutrient intake
Protein makes up 26.63% of your horse's total daily nutritional requirements by weight.
Poor topline and muscle development despite adequate exercise, slow hoof growth, dull or rough coat, weight loss or difficulty maintaining condition, slow wound healing, reduced milk production in lactating mares, and poor growth rates in foals and young horses.
Increased water intake and urination, ammonia-heavy urine odor in stalls, potential kidney stress over long periods, and wasted feed cost since excess protein is simply burned for energy or excreted. Moderate excess is generally well tolerated but is inefficient and expensive.
| Life Stage | Size | Min | Max | Unit | Notes |
|---|---|---|---|---|---|
| Adult | — | 630 | 800 | g | For a 500kg horse at light to moderate work. A standard hay ration of 10kg at 8-10% protein meets the lower end. Alfalfa supplementation boosts both quantity and quality. |
| Juvenile | — | 700 | 1000 | g | Growing foals and yearlings need higher protein for muscle and skeletal development. Lysine is the key limiting amino acid — ensure quality protein sources. |
| Pregnant / Nursing | — | 800 | 1100 | g | Late-gestation and lactating mares have significantly increased protein needs. Alfalfa hay and quality concentrates are essential during these stages. |
| Senior | — | 700 | 900 | g | Senior horses may need slightly more protein to maintain muscle mass, especially if they have difficulty chewing hay efficiently. |
| Working / Active | — | 700 | 1000 | g | Protein needs increase modestly with work intensity, primarily for muscle repair. Quality (lysine content) matters more than quantity for athletic horses. |
Source: NRC 2007
The fiber-to-protein balance determines hindgut health. High-fiber, moderate-protein diets support healthy fermentation. Low-fiber, high-protein diets disrupt the hindgut microbiome, increase ammonia production, and raise colic risk.
What this means: Maintain forage as the diet foundation (at least 1.5% body weight daily) regardless of how much concentrate is needed for work or growth. Never sacrifice hay to make room for more grain — the hindgut must keep fermenting. If energy needs are high, add fat rather than more grain.
