Amino Acids and Their Importance

What is an ”AMINO ACID”?

Definition: A simple organic compound containing both a carboxyl (--COOH) and an amino (--NH2) group.

But what does that even tell us? Why are they so important?

Horses have an Amino Acid requirement, not a crude protein requirement.

I’m sure we have all been taught this saying in school. Amino Acids (AA) are the “building blocks” to life, they are the smallest components to make up a protein sequence, and proteins are required for a multitude of bodily functions.

To go a step further, there are “Essential” & “Non-essential” AA.

Essential AA: What the body can’t synthesize on its own.

Non-essential AA: What the body can synthesize on its own. (not necessary to add into the diet) 

·         Lysine

·         Methionine

·         Isoleucine

·         Leucine

·         Histidine

·         Phenylalanine

·         Threonine

·         Tryptophan

·         Valine

·         Arginine


·         Cysteine

·         Glutamine

·         Glycine

·         Proline

·         Tyrosine

·         Alanine

·         Aspartic Acid

·         Asparagine

·         Glutamic Acid

·         Serine

·         Selenocysteine


Of the Essential AA’s the most important one to look at when considering a feed or AA supplement for horses, is Lysine. Lysine is the first limiting AA which means if a feed tag has a guaranteed analysis for Lysine at 3.5% then 3.5% of all other AA’s is all that will be available despite the other AA’s being at a higher percentage.

Below is a better way to visualize this limiting effect.  


Imagine that this barrel has holes where each AA is located. If you begin filling the cup with water, the water will start to leak at the Lysine hole first because it is towards the bottom. You can fill the cup up as much as you can, however that water will leak at the Lysine hole and not allow the Methionine and Threonine to be filled to their much higher levels.

Below is an example of a feed tag for a “light” feed. The Lysine is at 0.8% which means that even though the Threonine and the Leucine are above that, only 0.8% of them will be available

 Guaranteed Analysis of "Light Feed"

Below are two more examples, but performance type feeds. You can see that the level of Lysine is slightly higher than that of the previous feed. Amino Acids repair the muscle that is torn when a horse (or human) are under intense exercise, like a performance horse doing 3-day eventing or a reined cow horse working a cow in competition. But are these two feeds providing enough for even the most intense sport horses?

 Performance Type Feeds

Below is an amino acid supplement and the Lysine being well beyond any of the feed examples above at 40% crude protein. This is due to a low feeding rate as they are a supplement, not a feed. This will be top-dressed with the feed and only at a rate of 4-8oz/day. Most people lean towards adding an amino acid supplement to increase the muscling along the topline. As this is helpful, keep in mind that exercise and genetics play two major roles in developing a topline.

 amino acid supplement and Lysine

Looking at the ingredients of these two supplements (and ignoring the percentage of crude protein), these are the two most prominent feed ingredients for AA supplements. This is due to the unique AA profiles that Soybean Meal and Whey Protein Concentrate have. They are both bioavailable and soybean meal is an easily accessible source of protein for horses. There is some debate around soybean meal, or just soy in general, whether or not it is good for horses. However, it is important to do research to ensure that a reputable company stands behind their product before feeding it to your horse(s).

Now the real tricky bit: how much protein should my horse have?

By the recommendation from the NRC (2007), a horse only needs 1.72 grams of protein per kilogram of BW (For a 500kg/1100lb horse that’s 860g of CP).

How does this relate to the feed tag?

Taking the performance feed with the purple bag we can calculate if that feed is providing the minimum amount of protein in grams for your horse.

12.5% CP x 8# performance feed = 1# CP a day being consumed

There are 454.6g in 1# which means that horse is only getting half of the recommended amount of CP from its grain ration.

Hay analysis that was done back in 2019


Hay analysis that was done back in 2019 (from Wisconsin). 


 The CP is at 12.19% on a dry matter  basis.


A horse will eat roughly 1.5% of its body weight (BW) in forage a day, and with this horse weighing in at 1100# (500kg) which calculates to 16.5# a day.

12.19% x 16.5# = 2.011 # CP

2.011# x 454.6g/# = 914.36g CP

914.36 + 454.6 = 1368.96g CP





This is 508.96g CP more than this horse needs, however. This horse could be consuming less than the 1.5% BW in the hay, and could be eating pasture that’s lower in CP instead. Most grass hays are around 7-10% in CP which would range 525g – 750g which would drop the total down to 979.6g – 1204.6g CP which would be most ideal for this horse.  

A diet high in protein, or providing excess protein, will result in excess nitrogen that must be excreted as urea in the urine. Often times another result is loose manure or diarrhea that can be resolved with removing some of the protein in the diet.

However your horse is being fed, trusting a feed company to understand the amino acid makeups of feed ingredients is the best route to go. Soybean meal and whey protein concentrate are two of the most common feed ingredients for protein and are the best options for your horse. Not overloading your horse with protein will protect their kidneys and the barn (no ammonia smell!), and not to mention your wallet. Supplementing protein is expensive and owners often get too caught up on building a topline without taking into consideration their horse’s genetics and the exercise that is being accomplished.


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