Misconceptions About Protein in Horse Diets

Protein always seems to be one of the most important nutrients for horse owners when considering what to feed their horses. After all, protein is the first ingredient listed on a feed tag because it is so important for our horse’s health and performance. The protein content in our horse’s feed is also referred to in percentages to indicate just how much protein is in them. For example, a “10% horse feed” refers to a feed with 10% crude protein in it. However, as important as protein is, there are many myths on what protein does or how it can affect our horses.

Why Is Protein So Important to Horses?

Besides water, protein is the next major component in a horse’s bodily tissues. Protein is a major component of every cell in the body and has many critical functions. Some of the more important functions in horses include:

  • Skeletal muscle synthesis. Think about building the topline of a horse.
  • Building, health, and maintenance of connective tissue (tendons, ligaments).
  • Hormone synthesis. For example, insulin, glucagon, and reproductive hormones.
  • Ensuring proper growth in young horses.
  • Enzyme function. Protein is critical to digestive enzymes and those involved in blood clotting.
  • Maintaining overall blood function and maintenance of blood and other bodily fluids’ pH levels.

Protein is made up of a chain of amino acids. Our understanding of protein in horse diets is so advanced today that we now focus more on the amino acids in the horse’s diets rather than just overall crude protein levels. This is because not all proteins are created equally. High-quality horse feeds are now balanced by amino acid content, rather than just the amount of protein in a feed.

There are approximately 20 important amino acids for horses that can be classified into three groups.

  • Essential Amino Acids are those the horse cannot produce on their own and must be supplied by the diet. There are 10 essential amino acids for horses, which include arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
  • Nonessential Amino Acids are made by the horse’s body and are not required to be fed.
  • Conditional. When a horse is stressed or ill, they may need extra amino acid support in their diet.

You may have heard of the term “limiting amino acids.” This just means that there are specific amino acids that must be present in enough quantities in the horse’s body to make protein. If they are deficient, certain proteins cannot be made, which is why they are usually highlighted in horse diets. The limiting amino acids for horses are lysine, methionine, and threonine.

Misconceptions About Feeding Protein to Horses

When it comes to feeding protein, there are persistent myths that are heard around horse barns and online chat forums. Often, these can lead to poor decisions when it comes to feeding your horses. The most important takeaway when it comes to feeding protein to your horses is that many horses will achieve their daily protein requirements if fed a high-quality forage. Yet, the individual amino acid content will vary, depending on the type of forage fed. Thus, high-quality horse feeds available today are balanced with these deficiencies in mind and are still recommended along with feeding high-quality forage. Regardless, some misconceptions that persist include:

Myth #1: Feeding Higher (%) Protein Feed is Better for Horses

How much protein (or which amino acids) your horse needs will depend on a variety of factors. Young and growing horses need more protein in their diets to support their growth as compared to more mature horses. For example, a weanling at 6 months of age will need approximately 14.5% of their total diet (forage + feed) as protein. This is in comparison to an adult horse in light work who needs 10% protein of their total diet. Besides stage of life, what also needs to be factored in is what type of forage they are eating (grass vs legume), how much daily exercise are they receiving, underlying health issues, current body condition, and others. The take home message with protein is that more is not always better.

Myth #2: Protein is a Good Energy Source for My Horse

Protein, when digested, is broken down into its individual amino acids for its supportive function, as previously mentioned. This does not directly lead to providing energy to the horse unlike other nutrients. Yet, in extreme circumstances, horses can break down protein to use as an energy source. This often happens when they are in starvation mode and are desperate for energy to survive. Protein, even when fed in excess, is a very inefficient source of energy for the horse.

Myth #3: Feeding Too Much Protein Will Make My Horse Too Hot (Energetic)

Many owners will often confuse higher protein in feeds with other nutrients that are providing the higher energy to their horses. Much of the time, it is the higher levels of the nonstructural carbohydrates (NSC), or sugar/starch, that is giving the horse more energy, not protein. Some higher protein hays and horse feeds are higher in NSC or fat, which is where the extra energy in the diet is coming from. 

Myth #4: Feeding Too Much Protein Can Harm My Horse

When too much protein is fed, the horse will break it down and excrete it as urea. Horse urine that often has a strong ammonia smell is often an indication that the horse has more protein in the diet than it needs. There are no studies to indicate that feeding higher levels of protein damages a horse’s kidneys or any other body tissue. However, horses that have kidney dysfunction, or even liver disease, may need to have their protein levels limited.

Myth #5: Feeding Too Much Protein Will Lead to DOD (Developmental Orthopedic Disease) in Young Horses

There are no studies that link high levels of protein in the diet of a young horse and DOD. The major contributors to DOD are mineral and energetic imbalances. More can be read in our Feeding to Avoid Developmental Orthopedic Disease article HERE.

Take Home Message

There are many misconceptions about feeding protein to horses. Our best advice is to speak with an equine nutrition expert to assess your horse’s dietary needs. Our team would love to help you design a diet with the proper protein balance for your horse. Please contact us anytime for a free consultation to help you find the right protein balance for your horse.


National Research Council. (2007). Nutrient requirement of horses. 6th rev. ed. National Academies Press.

Article By: Chris Mortensen, Ph.D.
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