Myths and Facts About Protein


MYTH: Protein is a good source of energy for mature horses.

BUSTED: Of the three dietary energy sources—carbohydrates, fats and protein—protein is the hardest for horses to turn into energy. It is inefficiently utilized and produces more heat during metabolism than carbohydrates or fats. A feed high in protein may not be high in energy. Energy is what mature horses need most to perform at optimal levels.

MYTH: The higher the crude protein content, the better the feed.

BUSTED: Over the years, high-percentage crude protein feeds have been equated with quality because good quality proteins tend to be more expensive. Therefore, feeds containing high-quality proteins cost more and have been assumed to be better feeds for all horses. This is not always the case.

The percentage of protein needed by an individual horse varies throughout his lifetime. While a high-protein feed may be best for a younger horse, it may not be the best feed for a mature horse that has high energy and low protein demands. The percentage of crude protein alone does not indicate the type or quality of the protein in a feed. Not all protein is created equal. Young horses consuming the inappropriate levels and types of proteins will not grow properly even when supplied with adequate energy. Bottom line, you need to match the right types and levels of protein to meet your horse’s specific needs.

MYTH: Feeds high in protein “cause” kidney damage.

BUSTED: High-protein feeds do not cause kidney damage to healthy horses. Excess protein is excreted in the urine as urea. When a horse takes in more protein than he needs, he tends to urinate more and the urine is often stronger smelling. In the past this was equated with kidney stress. However, horses that have developed liver or kidney disease from another cause may be put on protein-restricted diets to ease the workload on the compromised organs.


FACT: Too much protein in the diet can cause health problems.

Unlike fats and carbohydrates, horses do not store protein for later use. Excess protein metabolism results in the buildup of nitrogen end-products, such as ammonia and urea. A diet containing excess protein will increase the horse’s water requirements and urine output as the ammonia and urea are flushed out of the body. Exposure to this strong urine can cause lung irritation and other airway problems.

FACT: Protein requirements change throughout a horse’s lifetime.

Protein requirements are dependent on the age, health status, and work load of your horse. Growing and reproducing horses need the highest levels of protein in their diets, which makes sense because new tissue is being created to sustain growth.

Hard-working horses are next in line as they are building new muscle and replacing damaged tissue on a regular basis. Sedentary and middle-aged horses that don’t work very hard have the lowest requirements of protein.

As they progress into their senior years, horses may need additional protein as the efficiency of their digestive tracts decreases. Horses with certain medical conditions may need more or less protein in their diets depending on their health issues.

FACT: The percent crude protein number on your feed tag is only one piece of the puzzle.

The “percent crude protein” found on the labels of feeds and supplements is a calculation of the nitrogen content of the product. Nitrogen is contained in the amino acids that serve as the building blocks of proteins. The word “crude” means that not all the protein reported by this number is digestible. It is estimated that between 2% – 5% of many common protein sources are not absorbed.

While the percent crude protein number is helpful, it should not be the sole piece of information used when choosing a feed or supplement for your horse. Crude protein does not tell you the source of protein contained in the feedstuff or the amino acid makeup of that protein. Percent crude protein is most useful when combined with information on the type of protein included in a product.

As we discussed Protein Demystified, lysine is the first limiting amino acid in a horse’s diet. Knowledge of the lysine content of a protein source is necessary when properly balancing your horse’s diet. Some labels will include the percentage of lysine found in a product. Knowing what ingredients are good sources of lysine and identifying those sources in the ingredient list will also help you make an informed decision.

Since all horses are individuals, we recommend you consult with your veterinarian or trained equine nutritionist to fine-tune the percentage of protein required in your horse’s diet.



  • Amelia Bolton

    can a horse have too many amino acids. Is there a maximum level?

    • Karen

      Hi Amelia,

      Amino acids are the building blocks of protein. As with anything, too much protein can cause problems. It is best to feed your horse at the recommended level of protein for his age and stage in life.

      When a horse is fed more protein or amino acids then they need, the horse excretes the excess as ammonia and urea molecules in the urine. In order to clear all the extra protein, a horse will increase his water intake and urinate more. Larger quantities of this noticeably stronger-smelling urine can lead to respiratory problems when a horse is kept up in a stall. Excess protein can also interfere with calcium absorption in young horses: Studies show that when 25% more protein than needed is fed to young horses, it can negatively impact growth rates.

      The best way to avoid problems is to feed the recommended amount of a high-quality protein to your horse. Below are the widely accepted rules of thumb to estimate the required protein in the total ration for different classes of horses. The total ration includes the following: pasture, hay, grain, and supplement.

      · Growing horses: feed 14% to 16% protein

      · Lactating mares, older horses: 12% to 14%

      · Mature horses: 8% to 10%

      Studies have shown that workload does not significantly increase protein requirements, as long as a horse’s digestible energy requirements (DE) are met.

      In order for a protein to be synthesized, all the necessary amino acids must be present at once. The amino acid whose supply runs out first and “limits” protein synthesis from proceeding is considered the “limiting amino acid.” For horses, lysine is the first limiting amino acid. In other words, it is the one most lacking in the equine diet; therefore, it is important to supply adequate levels of lysine in your horse’s diet. Growing horses, third-trimester broodmares and lactating mares have the highest lysine requirements.

      The National Research Council (NRC) estimates the daily lysine needs of mature 1,100-pound horses to be:

      23 grams of lysine for horses that are idle or in light work

      46 grams for horses in intense work

      More is needed in growing horses, depending on their age.

      Since lysine is the first limiting amino acid in the horse, the protein source utilized in the equine diet should be high in lysine, especially for growing and reproducing horses.

      · Soybeans are high in lysine and historically have been the ingredient of choice when formulating a good quality horse feed.

      · Soybean meal (the high protein part of the grain that has had the oil removed) provides excellent lysine levels.

      · Canola meal (not to be confused with rapeseed) is another source that provides adequate lysine for growing horses.

      · Animal sources, such as milk proteins, can also be considered.

      · Grains and grasses are typically low in the amino acid lysine.

      The following sources of protein can be found in equine feeds and supplements. Although they do provide lysine, they typically do not provide adequate levels for growing or reproducing horses.

      · Cottonseed meal

      · Linseed meal (not linseed oil)

      · Brewers grains

      · Distillers grains

      · Alfalfa

      · Corn gluten

      If you are feeding your mature horse a well-balanced diet that includes good quality forage and the recommended amount of a fortified balancer pellet or a commercial feed, your horse should be getting adequate levels of protein that include all the essential amino acids he or she needs.

  • Patrice Norell

    I recently had a trainer get upset about the protein level in Buckeye Ration balancer for my performance pony.
    I changed feed and now I am moving to a new barn that feeds … guess.. Buckeye Ration Balancer!

    I am confused as to what to do with the protein controversy between the two trainers.
    Is the protein level of a well known and respected ration balancer truly bad?

    • Karen

      Dear Patrice,

      The easy answer is no, the protein level of a well-known and respected ration balancer is not truly bad. It isn’t bad at all.

      It is easy for folks to get confused when dealing with percentages. 32% protein looks high at first glance, especially if you have been told that mature horses need between 10% to 12% protein in their diet. The key is, though, the 10% to 12% number is the percent protein in the entire diet. The balancer is just one small part of the diet. If you do the math and include the protein levels contributed by all the feedstuffs your horse eats daily (hay, pasture, supplements) you will quickly see that because you are feeding such a small amount of balancer, the balancer is actually providing the correct amount of protein when fed according to the manufacturer’s instructions.

      Thanks for the question. It was a good one!


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