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Chronic Protein Deficiency In Horses

This is a very important article for all horse owners to read and understand
I know that a lot of horse owners don't have time to read this, but I promise you that reading and understanding this article will be life altering for your horses.

If your horses are lame, if their top line is melting away, if skin disease plagues them, ask yourself why. Then read and understand why I think that most horses have a chronic protein deficiency. Doc T

What is Chronic Protein Deficiency In Horses you might ask. Well the answer requires a bit of information about proteins and I guarantee that you will find something useful in this article to take away when you consider what you are feeding your horse. This Free article is a direct result of the research I have been conducting for my Horsemanship Nutrition Course, but I’ll tell you more about that later. These are the important basics I want all horse owners to understand for the benefit of their horse.

The basics of proteins

Look at this sentence. It is made up of words and each of those words are made up of letters. There are 26 letters from which all the words are made and all the written thoughts in the books of our world are ideas expressed by the combinations of these words. 26 letters, enormous vocabulary, infinite written ideas.

Taking this one step further, look at the variety of books, magazines and newspapers in the world. All appear different and are made of different materials, yet all have sentences, words and letters. This is how all the things on this planet are made if you think about it - even you and your horse.

Books, magazines and newspapers are made up of a few basic parts: paper, cardboard, ink and glue or staples. Our body and the body of our horses are made up of 6 basic parts too: gas (air), water, minerals, carbohydrate (sugar), fat and protein. Of these, protein is the most interesting because all proteins are made up of only 20 building blocks called amino acids. Consider these the letters. These amino acids make up all of the proteins of the body. Proteins are like the words in a dictionary made of a finite number of letters, yet an enormous amount of information can still be expressed through unique sentences depending on how many words are used and where we place them.

Letters make words that in turn make sentences that create unlimited thoughts. Amino acids make proteins that in turn make structures that create unlimited living things on our planet.

Proteins basically provide the structure that makes us and every living animal we know into their unique shapes through the connective tissue of bones, ligaments, tendons, and muscle. They also make up a lot of other things in our bodies including defense mechanisms, sensors, and hair. I know this is basic, but I really want to get a few points across about protein in our horses.

Our alphabet is divided into two groups: the vowels (a e i o u) and the consonants (all the other letters). The amino acids in your horse are also divided into basically 2 types: non-essential amino acids (NEAA) and essential amino acids (EAA). This is VERY IMPORTANT. The difference between them is that NEAA’s can be made by the horse but the EAA’s need to be consumed pre-made in the meal. Imagine your book had only consonants (NEAA’s) but was missing some but not all of the vowels (EAA’s). The result would be a book that was hard to impossible to read.

If the diet of a horse doesn’t contain enough of the EAA’s then the horse will be deficient in many things such as connective tissue and immune function leading to lameness and skin conditions. Like a book missing some of the vowels, the horse may look like a horse but he will not work properly.

NEAA’s can be made from carbon, hydrogen, oxygen, sulfur and nitrogen consumed in the normal foods and the air we breathe. With this in mind, have you ever wondered why cattle can graze on poor land or be fed poor hay (”cow hay”) and still do well? Did you ever see a picture of a goat on top of a pile of garbage with a tin can in his mouth looking fat and happy? The answer is because ruminants like goats, cattle, sheep, and deer can manufacture almost all of their amino acids thus they have a low requirement for EAA’s. In essence, they can build most of their proteins from the molecules they consume. Ruminants still need all the amino acids a horse does but can manufacture most of them (the NEAA’s) while their need for consuming the EAA’s is low.

However you and you horse cannot manufacture about half of the amino acids we need to grow and maintain our bodies. These 10 or so amino acids need to be consumed in their complete form and are therefore are essential to maintaining life.

Remember, the wall of our digestive tract (stomach and intestines) is solid to large molecules such as proteins. Every protein we eat is broken down into their smaller amino acid building blocks or small groups of amino acids called peptides (like syllables of words) and these are absorbed through the intestines into the body. These amino acids and peptides are transported to individual cells and assembled into the proteins required by the cell. [As a side note, think of this the next time you buy an expensive joint supplement. What you are really feeding is a high quality protein high in EAA’s that is broken down by digestion into the basic amino acids and peptides and reassembled into what the horse needs. It would be just as good to feed your horse a less expensive high quality protein source.]

Here is an interesting fact about EAA’s. This fact I am about to describe occurs in humans and horses and once understood, will change the way you look at protein in both you and your horses.

When the minimum amount required in daily intake of just one EAA is less than 100% of what is needed on a daily basis, then none of the other EAA’s will be absorbed at 100% even when there is an abundance of the other EAA’s. Another way to look at this is to say that if there is not enough of the individual amino acids to build the protein, that protein won’t be made.

For example, EAA #1 requires 100 units a day and EAA #2 requires 500 units and EAA #3 requires 1000 units and so forth for all of the 10 EAA's required by your horse in a day of eating. Pretend that your horse consumes 200 units of EAA #1, 500 units of EAA #2, and 800 units of EAA #3. In this example, the horse is consuming 200% of what he needs of EAA #1, 100% of EAA #2, and 80% of EAA #3.

At first glance, you would assume that your horse is deficient in only EAA #3. In reality mammals have a system where if one EAA is at 80% of what they need, then ALL of the EAA's are at 80%. In this example, because EAA #3 is only being consumed at 80%, then every EAA this horse consumes is at 80% effectiveness no matter how much is eaten.

Enough good quality protein

It is important that your horse consumes enough protein, but it has to be of good quality (high in EAA’s) and it all needs to be absorbed from the gut into the body.

Crude protein is the absolute amount of protein in the feed. Unfortunately, some countries add urea to the feed to increase the crude protein value making the crude protein value suspect on any product. Many countries and the UN have started to use “True protein” or to list the individual amino acids as a way to see the protein content of food. This value does NOT tell you the quality or the availability of the protein for your horse. What is needed is the biological value of the protein which is the amount of protein that will be available for absorption past the wall of the intestines and used by the horse.

Not all proteins eaten are absorbed and used equally. Some have a tougher time breaking down and being absorbed ESPECIALLY if the intestines are inflamed by consuming inflammatory feed such as grain, grain byproducts, seeds and inflammatory oils. I have talked about gut inflation in some of my other blog articles and go into great depth in The Horsemanship Nutrition Course if you wanted to learn more. The percent of protein absorbed is sometimes called their biologic value (BV). For example, egg whites are completely absorbed, whey protein is about 96%, soybeans about 80% and grass and hay is about 50% to 65%. Also, some sources of protein also have limited amounts of EAA’s making these proteins poor sources of protein for horses.

The quality of the protein is based on the amount of EAA’s in the protein. The more EAA’s in the protein, the better quality it is.

The quality of protein can't really be measured in hay or grass because every batch of hay has a different amount. In fact, the only way to measure the total protein being fed is to measure the actual protein of the animal consuming it (killing it). Unfortunately this measurement is not a test you want to do on your horse. A rule of thumb holds though that the better the quality of hay or grass, the higher the quality of protein consumed and the reduced chance of a protein deficiency in your horse. The more stalk in the hay, the higher the fiber and the lower the available protein. Therefore, if your pasture and hay is of poor quality and your pasture and hay is limited in quantity, your horse is probably not getting enough good quality protein. They ingest enough protein to live, but not live well enough to become athletes.

The simple solution is to add good quality protein to your horse's diet.

Proteins in mammals don’t last long. The average life span of a protein is about 1 to 2 days. They degrade into parts and are recycled or are destroyed and excreted. They can live for a while, such as through the winter, without consuming good quality protein but at some point, they need to replenish what has been lost. Otherwise a chronic deficiency will occur which is the main thrust of my message here.

Horses in the wild consume a lot of good quality, live forage with good quality protein in the natural habitat during seasons when it is available. When winter comes and forage becomes dead or scarce or covered by snow then the recycled proteins are used. It holds them over until the spring grass returns. The protein shortage in the wild has a back up plan that gets them through tough times until good protein can return to the diet.

In my experience with horses kept by humans, they usually don't have access to a lot of pasture. Worse, access to good quality hay is limited by many factors including age of the hay, the way it was harvested, and the distance from the source. In fact, most barns have poor quality hay and it gets worse in the spring just before the new harvest is cut. If the horse can't get access to good quality sources of protein year after of year, then your horse could be suffering from a chronic protein deficiency. Specifically a deficiency in the proteins requiring the EAA’s.

It is a chronic deficiency because I have been with horses since 1973 and today I see more horses having so many medical issues that did not occur 40 plus years ago. Lame horses are at an epidemic level now followed by skin issues, insulin resistance and pituitary dysfunction (Cushing's). While vets now have tests and diagnostic equipment for these issues, no one is looking deeply for an answer to why they are occurring in the first place. Only superficial answers are given such as the intense show schedule, poor footing, genetics of today’s horses, poor training, etc. While all of these have a factor, I still believe there is a deeper underlying cause for all of it.

If the body is constantly breaking down protein just from the process of living (called entropy), it needs the building materials to repair itself. Add to entropy the additional wear and tear from movement and work such as jumping, galloping, collection, explosive starts and stops, endurance, and more. Where are the building blocks for repairing bones, ligaments, tendons, and muscles? Where are the proteins necessary for hormone and receptor creation, immune system charging, systems processing, and more? Proteins are essential for everything in you and your horse's lives and if you don't get enough protein and their EAA's and the reserves are used up, my hypothesis is that the horse will become sick, lame or both.

Another analogy may help explain this. If I delivered to you all the lumber you need to build a house, what house would you be able to build if I didn’t supply the nails? In essence, every horse being used for work or sport is stressing the muscles and other connective tissue in the process. To build this stronger structure is called conditioning the horse but requires the horse to have the materials to repair and strengthen the muscles, tendons, and ligaments. This material requires all the amino acids and especially the EAA’s.

My solution is simple and I would love to get everyone to start and then record their results. Add good quality protein to the horse’s daily intake, record all your observations, and be patient. Adding protein will require between 4 and 6 months to see the beginning results with maximum results in a year. You are basically rebuilding every cell in your horse's body. And by supplying the necessary building blocks in the EAA's, then everything will be repaired and strengthened.

An interesting fact here is that one bacteria cell has about 2 million proteins. A human has about 1 to 3 BILLION proteins in EACH CELL. A protein in a yeast cell is made of about 466 amino acids but some muscle proteins in humans are called titan proteins because they are made of almost 27,000 amino acids EACH. Next to water, proteins are the most abundant molecule in the body. Are you starting to see the enormity of the situation?

Is my horse consuming enough good quality protein?

The best indicator of good quality protein consumption is the top line because this is made of muscle only, which is almost all protein. There should be enough muscle on both sides of the spine to fill in the hollow otherwise seen in a poor top line. The Nutrena® company has created a “Top Line Score” - TLS. The back is divided into 4 sections and labeled with the letters A, B, C and D. It is interesting to note that the loss of top line in a horse always starts at the withers and progresses towards the croup (hips). Conversely, the withers is the last area to be filled in after increasing protein consumption.

The TLS goes like this -
A - all the top line is filled with muscle.
B - All the top line is filled with muscle except for the withers.
C - The croup and loin is filled with muscle but the saddle area and withers are not.
D - Only the area over the hips has muscle and the rest of the top line is absent.

Old horses often have a TLS of D with or without a sway back that I believe is predominately a chronic deficiency in protein. I am suspicious of the painful condition of kissing spine as a sequela of a poor and weak top line due to chronic protein deficiency and collapse of the spine tips upon one another.

I want to add a TLS of F often seen in very old horses.  The added sign of muscle loss is the absence of the masseter muscles (cheek muscles or jowls) leaving only the flat bone of the mandible.

The Body Condition Score - BCS - was created to judge the fat on horses. BCS 1 is a walking skeleton and BCS 9 is fat enough to float in water. A BCS of 5 is ideal but is not descriptive enough. For example, if a pasture horse has a BCS of 5 and a TLS of C, the owner would be told by others that the horse is underfed and encouraged to add weight. But a race horse with a BCS of 5 AND a TLS of A would be called an athlete just like our human counterparts.

Most trainers exercise the horse to improve the TLS but think again of the barn building analogy. The lumber is there (the horse) and there are plenty of carpenters ready to pound nails and build the barn (a training or conditioning system). But without the nails (EAA’s), no barn is built (the horse breaks down).

If excessive poor quality protein (without the EAA’s) is consumed, then the production of required protein in the body is curtailed. However, the protein not used in the diet is then consumed for energy creating urea, a byproduct from the nitrogen in all the amino acids. If you smell ammonia in the urine, it is because your horse is consuming excessive amounts of poor quality protein, is inadequately making the proteins necessary for body maintenance and growth, has a poor hair coat and hoof, has a poor TLS, may be lame, may have skin conditions or is unthrifty and the urine and barn smell like ammonia.

Where do horses get good quality protein and what exactly should they be eating?

Horses in the wild consume a variety of forage (grass, leaves, and other vegetation) and they consume it throughout the day. This is not the case with horses in captivity on poor or little pasture and suspect quality hay. With this in mind, I want to go deeper into the discussion of amino acids because there is more to understand before you can help your horses. Stay with me.

I said that there are about 10 EAA’s but you might say so what? Horses in the wild must get them so why not just turn them out in a big field? You might also say that your horses basically look good and are performing well enough. In essence, you would be right - for most horses. Because of the sub-clinical effect of chronic protein deficiency, you often won’t see its effect until it is too late (lameness) or the horse ages and the top line is lost. Because this deficiency is possible in most horses fed by humans, it is necessary to learn about the 3 “Limiting Amino Acids” (LAA’s).

The LAA’s are the EAA’s that are found in limited supplies in nature. They are lysine, methionine and threonine. Looking at the 3 limiting EAA’s and what they do in the horse will help you understand why it is important to give enough of a high quality protein to your horses every day.

• Lysine - promotes bone growth in foals and maintenance of the connective tissue (bones, joints, tendons, ligaments, etc) in mature horses. A deficiency may cause a variety of developmental orthopedic diseases in the legs of young horses and in adults may cause the breakdown of suspensory ligaments, tendons, joints and other structural components.
• Methionine - growth and maintenance of hair coat and hoof structures. A deficiency often causes a poor hair coat and poor hoof quality (cracks, crumbles). See more below.
• Threonine - overall growth, muscle mass maintenance, production of adrenaline and other important hormones. A deficiency often causes poor body condition, a poor TLS and lack of energy.

You might recognize methionine because it is often added to hoof supplement such as biotin. It is one of 2 EAA’s that have sulfur in it. Sulfur has the ability to attach to the sulfur of another amino acid with a sulfur molecule and this is called a disulfide bond. This bond causes the amino acid to fold upon itself and become structurally stronger.

Now that I told you this, let me say that methionine doesn’t create disulfide bonds. Confusing I know, however, methionine is converted into cysteine that is converted into cystine that not only has strengthening disulfide bonds, but makes up about 24% of the protein in the hoof. Without methionine, cystine cannot be made. It is considered by some that the inflammation in the laminae (laminitis) causes the breakdown of the disulfide bonds which causes the coffin bone to separate from the hoof wall. Another hypothesis would suggest that providing enough protein, specifically methionine, would help prevent laminitis as well as hoof cracks and poor hoof quality. This is why methionine is added to hoof supplements. However, to be effective, there must be enough of all the EAA to create, maintain and repair all the proteins of the hoof. Remember that while 24% of keratin is cystine, the remaining 76% is still protein. However, with a deficiency in the limiting amino acid methionine in the natural diet, and subsequent deficiency in cystine available with their disulfide bonds PLUS the deficiency in other EAA’s, the hoof will struggle to maintain itself against the rigors of shoeing and training.

If your horse is prone to laminitis or has poor quality hooves, it may be valuable to add a good quality protein source. While I can see no downside, it must be remembered that it takes a year to grow a new hoof so adding protein won’t fix a deficiency right away. But the sooner you start, the better off the horse will be.

Lysine is critical for almost every protein in the horse (and you) because it helps to make the other proteins available for use. Without lysine, the remaining amino acids and proteins just aren’t as abundant to do their jobs. Lysine is the number 1 limiting EAA and it is often not available in large enough quantities in grass and hay. Lysine is the FIRST key to unlocking protein efficiency and supplementation and is essential for horses kept in our care today.

If you still have questions about what exactly is happening with digestion, we dive even deeper in The Horsemanship Nutrition Course.

What protein should I feed and how much?

The simple answer is from ½ to 1 gram of protein per pound of body weight depending on the needs of the horse.

Let’s do some math. If you are feeding a pound of grain with 10% crude protein in it then how much protein is your horse getting? 1 pound = 454 grams. 10% of 454g is 45.4g of protein. Because this is crude protein, we need to determine the true protein source. If it is alfalfa meal, oat hulls, and other assorted vegetable protein sources (read “by-products”), then we need to divide 45.4 by 2 (50% availability) which equals about 23g. Even with this knowledge, if you can’t determine exactly what amino acids are in this, then this 23g could be deficient in the LAA’s and other EAA’s.

Your 1000 pound horse is also consuming protein in the hay and pasture, but how much and of what quality? If a horse eats about ½ of a 40 pound bale of grass hay a day, then he is consuming 20 pounds or 9080g. Good quality grass hay has about 10% to 16% crude protein - lets use 16%. 16% of 9080g is 1453g. Now crude protein needs to be digested and the biological value of grass hay is about 50%, so half of 1453g is about 725g. If the goal is to consume 0.5g to 1g of protein per pound of horse per day (500g to 1000g per 1000 pound horse), then you are right in the middle at 725g from hay plus 23g from the pound of grain (748g).

But are you really? Remember the 3 limiting EAA’s that are often missing in a natural diet? Add to this that you are using your horse for athletic purposes requiring conditioning that is building connective tissue? Then is 748g of suspect quality protein enough? In my mind, every horse needs to have added to this diet an additional source of good quality protein that is found in soybean meal and whey protein isolate because they add the missing EAA’s, and specifically the LAA’s.

Continuing with this horse, let’s increase his requirement to 1g of protein per pound so we want 1000g of protein. He is about 250g shy which can be achieved by adding 266g (0.59 pound) of whey protein isolate (94% absorbed). You will need 312g (0.69 pounds) of soybean meal at 80% availability to also achieve this goal. From this additional protein you should have enough EAA’s and LAA’s to prevent the consumption of fed protein for energy (urea production) and to build the proteins necessary to prevent the problems of chronic protein deficiency.

There are several commercial products containing soybean meal or whey protein isolate in combination with minerals, vitamins and a carrier base. Be careful of the carrier base as it is often corn though in most horses this small amount won’t be a problem. When I started working with horses in the early 1970’s, we had a bag of straight soybean meal which we added a scoop (I can’t remember how big but maybe a quarter cup) once a day. Now I recommend either Manna Pro’s Calf Manna with corn (inflammatory and may reduce protein uptake) or Nutrena’s ProAdd Ultimate without corn. (CAUTION - THESE PRODUCTS HAVE CHANGED THEIR COMPOSITION AND I NO LONGER RECOMMEND THEM AS OF LATE 2018 GO TO: PROTEIN FOR HORSES REVISITED). There are others but beware of protein products that have “various vegetable proteins” as a source combined with soybean oil (may be inflammatory), corn (inflammatory) and molasses (unnecessary and inflammatory).


First of all, I am not affiliated with any company nor do I sell any supplements or protein products. I only want to create a conversation and develop thoughts that will inspire you to think and start making better decisions in keeping your horses.

Second, if your horse has any health issues, especially kidney problems, then consult with your veterinarian first.

My recommendation is to 1) stop feeding sugar (grain, grain byproducts and all supplements including treats, carrots, sugar cubes, apples etc.), 2) increase pasture and good quality hay (grass and some legume) consumption, and 3) add 1.0 pound of soybean meal, whey protein isolate, or a soybean meal/whey isolate combo protein to the daily intake for your horses weighing 1200 pounds (545 kg) (1000 to 1400 pounds or 454 - 636 kg).  Have unlimited access to water and mined salt (rock salt or Himalayan). Further, I highly recommend starting a diary to record every possible observation and commit to this diet and chart for a year. If you feel capable, after a year write a summary of your observations and send it to me with permission to post and help me get the message out.

Remember, if you don’t like the results you are getting you can always return to your original diet. No harm done.

The Horsemanship Nutrition Course

Believe it or not this is just scratching the surface on Horsemanship Nutrition. If this article has left you wanting to learn more. If you are the type of horseman that wants to know everything you can do to improve the health and well being of your horse. The Horsemanship Nutrition Course is going to give you that in depth look into everything that goes on with your horses's diet needs.

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