Ideal Amino Acid Balance

By: Dr. Bill Vandergrift

Amino Acids

Amino acids are the building blocks of proteins; without them your horse would not be able to survive.  There are approximately 22 amino acids that are combined together to form the majority of proteins in your horse’s body, although there may actually be more than 200 amino acids found in nature.

Ten amino acids are considered dietary essential for the horse meaning that these specific amino acids must be present in the horse’s diet because the horse’s body is not able to synthesize them.  The remaining 12 amino acids can be made by the horse as long as the horse has an adequate supply of protein in the diet.  If the diet does not contain enough protein for the horse to make the non-dietary essential amino acids the horse will break down body tissues, muscle for example, in order to obtain the protein it needs to make these amino acids for more critical functions.  A good example is a lactating mare needing to break down body tissue in order to obtain enough amino acids to make milk for her nursing foal.

The ten dietary essential amino acids for the horse are lysine, threonine, methionine, tryptophan, leucine, isoleucine, valine, histidine, phenylalanine, and arginine.  Of these, lysine,  is considered the first limiting amino acid meaning it is the amino acid that is most likely to be deficient in your horse’s diet.  Therefore, if your horse’s diet contains an adequate amount of lysine then your horse’s diet will also contain an adequate amount of protein and the remaining 9 dietary essential amino acids.  If this is true then why do you often see multiple amino acids guaranteed on a feed tag; is it even necessary to guarantee these also?

Amino Acid Balance

The reason multiple amino acids are guaranteed on a horse feed tag is to provide the horse owner with assurance that a particular feed not only provides an adequate level of protein and amino acids but to also demonstrate that the amino acids are present in a properly balanced proportion to each other.  The closer dietary amino acid levels are to what is considered an ideal amino acid balance the more efficient the horse will utilize those amino acids for protein synthesis and metabolism in the body.  When amino acids are not properly balanced excess levels of individual amino acids will be utilized by the body as an energy source rather than a protein source.  The process of converting amino acids into energy is an inefficient process that generates heat and forces the horse to excrete greater amounts of water and electrolytes compared to a horse receiving a more balanced supply of amino acids.  The excretion of greater amounts of water and electrolytes due to excess amino acid intake reduces a horse’s heat tolerance and stamina resulting in reduced performance.  Non-performance horses and horses with light workloads may not exhibit problems in this regard, but horses performing in more intense (power and/or duration) exercise will definitely feel the negative effects of excess amino acid intake.

Ideal amino acid balance for horses is determined by the proportion of individual amino acids found in equine muscle.  When dietary amino acids are provided in the same proportion as the amino acids found in the horse’s muscle then the horse utilizes dietary protein and amino acids in a more efficient manner thereby increasing stamina and performance as well as overall well-being.  Since lysine is the first limiting amino acid as discussed previously, ideal amino acid balance for individual amino acids is expressed as their proportion to the amount of lysine found in the horse’s muscle (Table 1.).


Table 1:  Dietary essential amino acid balance in equine muscle.
Amino Acid Proportion to Lysine
Lysine 1.00
Threonine .61
Methionine .27
Tryptophan .20
Leucine 1.07
Isoleucine .55
Valine .62
Phenylalanine .60
Histidine .58
Arginine .76


Optimal dietary amino acid balance compares the proportion of dietary essential amino acids in the horse’s diet to those found in equine muscle.  Table 2 compares the dietary essential amino acid balance in Triple Crown feeds to ideal amino acid balance. (Note: dietary amino acid levels should be equal to or greater than “ideal” but as close to “ideal” levels as possible for optimal amino acid and protein utilization by the horse.)

Functional Amino Acids

A functional amino acid is an amino acid that supports a specific physiological function when provided at levels greater than required for normal protein synthesis and metabolism.  Common examples include arginine which generates increased levels of nitric oxide and leucine which promotes muscle development when fed at levels greater than required.  While these functions may be desirable in some cases it must be kept in mind that when these dietary essential amino acids are fed out of balance they can interfere with optimal protein and amino acid utilization.  Therefore, amino acids should only be fed at their functional level when the function they support (ex: nitric oxide production or muscle development) is more important for an individual horse than efficient protein and amino acid metabolism.  There are times in an individual horse’s life when these functions take priority but providing amino acids at their functional levels should be done only when justified and not as a general daily practice for all horses.

Amino Acids and Topline

Research has demonstrated that some horses with weak toplines benefit from additional dietary amino acids.  Some important points to consider in achieving a stronger topline include:

  1. Is the weak topline being caused by structural issues or digestive dysfunction? If so, these items should be corrected first before considering an amino acid supplement.
  2. Is the horse presenting with metabolic issues such as PPID or old age? If so, there will be a limit to how much additional protein and amino acids will benefit.
  3. Is the horse receiving adequate exercise to support improved muscle condition and development? If not, the exercise program will have to be adjusted
  4. If the horse is a candidate for amino acid supplementation ensure that leucine is included in the supplement because leucine is the most important amino acid for muscle development.
Table 2.  Selected Amino Acid Levels of Triple Crown Feeds Compared to Ideal Amino Acid Balance

Triple Crown Feeds Provide the Amino Acids Your Horse Needs

Getting enough essential amino acids is key to the development and overall health of your horse. Triple Crown ensures our fixed formula feeds will always provide your horse with the essential amino acids and nutrients they need to succeed.

Take a moment to compare your feed to Triple Crown-