A beginner’s guide to protein and amino acids for horses

This overview of protein and amino acids will help you better understand these vital nutrients and how they affect your horse’s overall health.

Protein makes up approximately 15% of total body mass. After water, it is the most abundant substance in your horse’s body.  When he consumes protein, it’s broken down into individual amino acids and absorbed into his bloodstream. These amino acids can then be used to build different protein chains for the body, forming enzymes, cell structures, muscle protein, connective tissue, hooves, hair and more. Let’s take a closer look.

Crude protein

Crude protein is the term you see listed on a hay analysis or guaranteed analysis. If you walk into a feed store and ask for a horse grain, the salesperson might say something like, “Sure, I have a 10% and a 14%, which would you like?” Don’t be fooled – this is a trick question. The percentage, which refers to the amount of crude protein in the feed, doesn’t matter as much as the amount that needs to be fed. In other words, a higher percentage doesn’t necessarily mean your horse will receive more protein. For example, if you feed a ration balancer that is 30% protein with a 1 lb feed rate, your horse is getting 130 grams.  Compare that to 22 lbs of hay with 5% protein – that provides 499 grams.

Let’s compare some numbers:

Your average 1,100 lb horse in light work needs 699 grams of crude protein per day.

According to Dairy One, the average amount of protein in grass hay is between 7% and 14%. As you can see from the chart above, hay will meet the daily crude protein requirements for most horses at maintenance or light work.

What about concentrates? The chart below compares various concentrates using the manufacturer’s recommended feed rate for a 1,100 lb horse in light work.

Amino acids

Meeting crude protein requirements is only part of ensuring your horse has adequate protein. He also needs adequate amino acids.

Amino acids are the building blocks of protein. There are 21 primary amino acids, which are broken down into two main categories: non-essential (dispensable) and essential (indispensable). Non-essential amino acids can be manufactured by the horse. Essentials need to be provided through the diet.

Think of amino acids like individual letters of the alphabet. You need to put those letters together to build a word, or in this case, a protein chain. Let’s say your horse needs to build some muscle. He pulls the specific letters from his amino acid alphabet to form the protein chain: M U S C L E.  But what happens if he has run out of the “U” amino acid? Then his protein chain would look like this: M   S C L E.  Without the “U”, the protein chain for muscle cannot be formed.

Your horse will pull the most important protein chains – the ones he needs for survival – from his amino acid alphabet first. Areas such as topline and hooves come afterwards. If there are not enough amino acids left over, he cannot form these protein chains. The missing ones are called “limiting amino acids” because the amount a horse has limits the amount of protein that can be made. The most limiting amino acids for your horse are lysine, methionine and threonine (see below).

Another great analogy is Liebig’s Law of Minimum. Take a look at Liebig’s barrel (at right) to see how protein chains are limited by the amino acid in shortest supply.

Protein sources

Feeding a variety of protein sources is key to ensuring your horse has an adequate supply in his amino acid alphabet. Each protein source has different amino acids that your horse will break down and re-use. Examples of various protein sources include grass, hay, legumes, grain, flax, wheat middlings, split peas and chia seeds.

Adding protein to a diet can also add calories. This can be tricky for easy keepers who need protein but not the calories. For these horses, a protein supplement is best. Whey protein isolate is a high quality protein source; 1 oz (28 g) will provide approximately 25 g of protein. This can be combined with flax or chia to add to the amino acid alphabet without the extra calories.

Limiting amino acids – how much does your horse need?

Lysine is the most important limiting amino acid. It is the only one the NRC has a minimum requirement for. The current requirement for a 1,100 lb horse in light work is 30 g per day. Since there are no set requirements for methionine and threonine, one can look at the ratios of amino acids in the horse’s muscles – 100% lysine, 61% threonine and 27% methionine. Based on these numbers, a safe guess for supplementation is 2.5 g to 5 g of methionine and 2 g to 4 g for threonine, but talk to your vet to determine an appropriate dosage for your horse.

The importance of reading labels

A lot of supplement and feed companies have jumped on the “topline” and amino acid bandwagon, yet their products contain miniscule amounts of amino acids. Some even claim to have miraculous results, yet the ingredient levels are clearly too low to back up their claims, and they carry a high price tag. If the amounts per serving are not listed on the label, call the company directly. Ask them how many grams per serving of amino acids are present to ensure you are paying for something that will truly fill your horse’s amino acid alphabet.

As you can see, providing your horse with adequate protein can go much further than a number listed on a feed tag. Your horse will receive more protein from quality forage than concentrates. If he needs additional protein, feeding a variety of sources will help ensure his amino acid alphabet is complete.