Last Updated on April 7, 2022 by Allison Price

Protein is the most important nutrient for horses, after energy. Protein is essential for building good quality hoof, skin, hair, organ tissue and muscles as well as blood, blood, and bone. A horse’s diet must include protein as it is an essential part of hormones, enzymes, and other hormones. It is the second most abundant substance in horses’ bodies after water.

Proteins are not nutrients. While some proteins are very high-quality, others can be so poor that horses may not be able to grow, reproduce, or build muscle. So what determines protein quality? Let’s first look at what proteins actually are.

What is PROTEIN?

Proteins are long chains made up of small molecules called amino acid. You can think of amino acid chains as trains that connect with each other to create a protein “train”. Proteins, also known as amino acids, are organic compounds that contain carbon, oxygen and hydrogen.


21 amino acids can be combined in nearly limitless combinations to make proteins. Horses can make up to 12 of these amino acid in their own bodies. They are called non-essential amino oils. Six of these amino acids, which are not essential, must be included in the horse’s diet under certain circumstances like illness or growth. These are known as “conditionally essential amino acid” (or simply “essential amino acids”). The remaining 9 amino acid are called ESSENTIAL amino oils. These essential amino acids are not possible to make in horses and must be provided by the horse’s diet.

The three most important amino acids for horses are lysine (threonine), methionine and methionine.


Although it is possible and likely for horses to absorb high-quality bacterial protein from their hindguts, the majority of horse’s protein requirements are met by what they eat. It is important to feed high quality protein.

The quality of a protein is determined by its ability to meet a horse’s amino acid requirements, especially the essential amino acids. A high-quality protein will have amino acids in a similar amount to what a horse requires. Low quality proteins may not contain enough essential amino acid to meet the horse’s needs or will be unavailable for absorption.


Different feeds have different amounts of essential amino acids, so they can vary in quality. In general, grass hay and pasture contain lower quality protein than legumes hay or pasture like clover/alfalfa/lucerne. Also, C4 types grasses have lower quality protein than those of C3.


Cereal grains such as oats, barley, and corn have lower quality protein than legumes like soybeans, lupins, and beans. Co-products such as copra meal are in the middle, with lower quality protein than legumes but higher quality protein than cereal grain. Heat treated cottonseed meals is the most common ingredient in horse feed. It contains the least quality protein. Soybean is the most concentrated and well-balanced source of essential amino acids, making it the best vegetable protein.

Whey protein is the absolute best in protein quality. Whey protein has a high level of essential amino acid, which matches almost perfectly horse’s protein needs. A small warning: Whey protein should not be used in horse diets. You need to make sure you buy’whey proteins concentrate’, and not whey powder. Whey powder contains more than 50% lactose and only 13% protein, making it ineligible for horse rations.


Horses do not need to consume a lot of high-quality protein. Horses in good health, including those in early pregnancy or in dry conditions, have moderate to low protein needs. They can be easily provided with hay and grass of average quality.

High quality protein is essential for horses that are growing, lactating, or late pregnant. High quality protein is essential for these horses to be able to perform at their best. For best results, hay-based diets or grass pasture should be supplemented by legume hay or grains. This is why horses who need to gain weight should consider adding alfalfa/lucerne hay (see our post 7 easy steps to putting weight on horses). Below is a table showing the % crude protein as well as the g/kg of Lysine in common feed ingredients.

Whey Protein Concentrate8089.8
Soybean Meal4530.1
Soybean (Full Fat).3723.3
Canola Meal3721.1
Faba (Tick Beans)2414.8
Germs for Wheat2314.7
Cottonseed Meal*3614.7
Linseed Meal3211.8
Sunflower Meal3211.0
Copra Meal218.4
Lucerne Hay178.0
Rice Bran147.0
Palm Kernel Meal176.4
Wheat pollard146.3
Wheat Bran145.6
Black Sunflower Seeds295.1
Soybean Hulls124.7
Sugarbeet Pulp94.0
C3 Type Grass Hay113.8
Oaten Hay83.0
Hay of the C4 Type Grass92.8
Wheaten Hay82.8
Corn (Maize).102.8
White rice82.7
French White Millet112.1
Oat Hulls41.8
* Although cottonseed meal may appear to contain moderate amounts of lysine after heating, a toxic compound called Gossypol bonds to lysine during oil extraction. This makes it safe, but also renders the lysine indigestible. The digestible levels of lysine are much lower than that.


FeedXL Pro and Advisor plans include Lysine in the nutrition analysis of horses’ diets. Your horse will get the quality protein it requires by making sure your horse’s diet contains both crude protein and lysine.

Low levels of lysine in your diet indicate a low quality diet. These situations will limit your horse’s ability use the protein in the diet to grow, reproduce and build muscle. The following steps are recommended to raise lysine in horses whose diet is low.

  • Substitute alfalfa/lucerne, clover pasture, or hay to your diet. This will add up to 1 kg/100kg of bodyweight (1 kg/100lb bodyweight). This will be sufficient in most cases.
  • Look for complete feeds that include high-quality protein legumes. If you make your own feeds, add legume grains such as soybean, lupins, faba beans/tick bean/field beans to the diet. Avoid feeds that contain cottonseed meal and unnamed vegetable protein meals.
  • You can use small amounts of whey concentrate or whey-protein based products. The whey protein should not be consumed within the first 15 minutes after the horse has completed an exercise session.

Lysine supplements can also be purchased and used to increase lysine levels for horses. However, FeedXL’s measurement of lysine in horses’ diets is a good indicator of overall protein quality. You can increase lysine levels by adding legume hays, grains, or whey. This means that you are adding methionine, the rest of the essential amino acids, and also lysine. Although purified lysine can be used to fill a specific lysine shortage, it could also cause unquantified deficiencies in other essential amino acids.


When looking at protein in your horse’s diet, always remember ‘proteins ain’t proteins’. Some proteins have high levels of essential amino acid and are therefore very good quality. Others are lower quality and less quality depending on the amino acid composition. High quality proteins such as those from legumes like lucerne/alfalfa or grains like soybean can support growth, pregnancy and muscle building. Low quality proteins such as cottonseed meal or cereal grains won’t be able to properly support horses that have high requirements for quality protein.

Although horses do not require high-quality protein, if your horse has a lot of work to do, such as when she is pregnant, lactating or growing, the quality of the horse’s diet will be a major factor in how well he performs. FeedXL Pro can help you monitor the quality of your horse’s diet and alert you if it is low.

Allison Price
Allison Price

I’m Allison, born and raised in San Diego California, the earliest memory I have with horses was at my grandfather’s farm. I used to sit at the stable as a kid and hang out with my Papa while he was training the horses. When I was invited to watch a horse riding competition, I got so fascinated with riding!