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The Importance of Protein – Decomplexicating Equine Nutrition Part 8 of 12

I know this is getting very detailed. Read this anyway. Print it and then mark it up with a highlighter. Ask your barn friends to test you on it. Become a student. Become your Horse's Advocate.

But for those who feel overwhelmed, don't weave in your stall. I am going to summarize everything into a simple plan of how to feed your horse in the coming weeks. I am also turning this into a course for those wanting to dig in deeper or go at a slower pace with some guidance. Stay tuned!

When discussing nutrition, most people know more about sugar as it is in the news every day. Fats are also discussed in terms of good and bad fats. However when it comes to proteins, most people immediately recite the % protein content of the feed they are giving to the horse. So let’s start there.

Crude Protein

When a bag of anything says % crude protein, what they are telling you is if they took a quantity of that feed (grain, hay, potato chips, soda - anything) and burned it to nothing, they would measure the amount of Nitrogen burned off. Comparing that amount against the total amount would yield a %. Nitrogen is only found in air and in protein so the assumption is that any nitrogen found in the burn off is related to protein. Dog food made outside of the United States was infused with urea which is toxic to animals and is made with Nitrogen. When this food was analyzed the % protein was listed higher than it really was as it only measures the Nitrogen and not the ingredient it came from. This dog food killed dogs and has been removed from the market.

The result is that when you purchase any food for the horse that is a mix of ingredients, you need to read that ingredient list to determine the source of nitrogen. What I mean by a mix of ingredients is any bag of grain or supplements or treats. Usually the crude protein of all hays is a reflection of hay protein but of grain, the protein sources could be from alfalfa pellets, soybeans, corn, or wheat middlings. This makes a big difference because the proteins from each of these ingredients are absorbed differently.

To put it in a simpler way, not all proteins are the same! Therefore not all proteins are absorbed the same way. So far, you now know that feeding “12%” protein doesn’t tell you anything. You MUST know the ingredients to determine how much protein your horse is actually getting.

Amino Acids

Remember in past blogs that the gut wall is very thin with tight junctions whose main purpose is to keep bad things out of the body but also let in good things like the raw materials called nutrients? Proteins consumed whole are very large molecules that cannot pass through the gut wall. So how do they get in? There are two ways but both are part of one process. Like two ways to get to the local store - by car or by horseback. The process is to take every protein in food and break them down into the individual parts called amino acids. These are small enough to be taken through the gut wall and into the body where the horse assembles them back into the proteins they need.

To repeat, every protein consumed by the horse is taken apart or disassembled into tiny pieces, transported across the thin gut wall and then reassembled on the other side, within the cells of the horse and by the cells of the horse into the specific proteins it needs. This process happens with every protein consumed but it is more efficient with some proteins than with others. This efficiency is called the biologic value of the protein and egg white is the standard with 100% efficiency. Every bit of egg white will be absorbed across the gut wall and into the horse. 94% of whey protein will be absorbed. 80% of soy bean protein will be absorbed. About 50% of grass and alfalfa protein will be absorbed.

In other words, if a pound of each protein source is fed to a horse, the following amounts will be absorbed: egg 1 pound, whey 0.94 pound, soy 0.8 pound, and hay / pasture 0.5 pound. The ingredients matter not just the crude protein. If you feed a pound of bagged food containing 14% crude protein and the ingredient source of this protein is only alfalfa meal, then the net absorbed protein is 14% of 1 pound (0.14 pound) times 50% absorption yielding 0.07 pound absorbed protein per pound of feed given.

Hold this thought that only a portion of the protein fed is actually absorbed. I’ll get back to this in a moment but I said that there were two paths within the same process of getting proteins into the horse. The process involved breaking them down into amino acids and transporting these to the cells where they are assembled into proteins again. But amino acids come in two types: those that can not be made by the horse (essential amino acids) and those than can be made (non-essential amino acids). It is the essential group that needs to be fed in enough quantities to effectively make the proteins the horse needs. Out of the 20 total amino acids that make all of the proteins in the horse, 10 need to be consumed by the horse and the other 10 can be made from the atoms inside the cells. 3 of these essential amino acids are called “limiting” amino acids because they are limited in the food sources of horses.

Making matters of protein manufacturing more difficult is that every protein made needs all the amino acids needed for that protein.

For example, what if I wanted to write this blog but my computer could not type the letter “e.”

The sentence would look like this:

For xampl, what if I wantd to writ this blog but my computr could not type the lttr “.”

In other words, if the horse is missing or is limited in even one essential amino acid, then there are a lot of proteins not being made. To get these limiting amino acids the horse can do two things. The first is to consume them by finding them in his environment and the second is to recycle the essential amino acids already in the body. The recycling program is very effective and works well but there is always some attrition so the horse still needs to take in some of these essential amino acids. See Fact 5 below for more on this important point.

Interesting Facts About Proteins

Before looking at why most horses today are protein deficient, let’s review what we do know and add some more facts.

Fact 1 - Proteins are very important in the body making up every working part including immune system molecules, hormones, neurotransmitters, connective tissue and hair and hooves. Think of sugar and fat as fuels. Also think of fat as cell walls and insulation around nerves. Think of everything else as proteins.

Fact 2 - Proteins are very small but too large to be absorbed through the gut wall. They have not been photographed or seen in a microscope. There are estimated to be between 1 and 3 BILLION proteins within every cell. For perspective, count how many molecules of gasoline are in your filled gas tank of your car.

Fact 3 - Proteins have a life span. With the exception of hair and hooves, the life expectancy of a protein is about 2 to 4 days. When the protein life is over, the amino acids go into the recycling program and used to make new proteins.

Fact 4 - A very interesting fact about horse hooves is that 24% of the hoof is made of 1 amino acid - cysteine. It is the only amino acid that has a Sulfur molecule in it that can make a special bond that folds and strengthens it adding rigidity to the hoof. But the horse can only make cysteine if he eats protein with the essential amino acid methionine. This essential amino acid has the Sulfur atom but cannot make this special bond so the horse converts it into cysteine before making the protein of the hoof. Oh, and guess what? Remember that I said there were 3 limiting essential amino acids in the horse’s environment? One of them is methionine. The result of taking in food (raw materials) low in methionine is poor hair coat and hooves.

Fact 5 - If you are low in one amino acid then you will be low in all the amino acids even if they are available in abundance. This makes a lot of sense once understood. The best way to describe this is to think of a protein as a word and the amino acids as the letters making that word. For example HORSE is made of one letter each of H, O, R, S and E. If I gave you 7 H’s, 16 O’s, 7 R’s, 4 S’s and 30 E’s, how many times would you be able to spell “HORSE” The answer is 4 because you only have 4 S’s. You might be able to make some other words such as “HOE” and “HERO” but you cannot make another “HORSE.” Therefore the S is a limiting letter and if it was an amino acid, it would be a limiting amino acid. Not all proteins eaten as a raw material will have all the essential amino acids needed to build all the proteins that make a horse work and remain healthy. This is why a horse needs to be fed a wide variety of proteins to supply a wide variety of proteins. Soy bean is the least expensive, most abundant and most complete protein source for horses with a high bioavailability.

Fact 6 - The body can take protein in the form of muscle and convert it into 2 products: glucose and urea. This is called gluconeogenesis (glucose new birth). The glucose is used for energy in the mitochondria and the urea is excreted in the urine giving the ammonia smell in the closed barn in the winter.

Fact 7 - The daily requirement for protein intake to replace amino acids lost in attrition is debated in the human world Several factors need to be looked at and will be covered in the next section. According to the National Research Council which sets the standards for animal nutrition, the recommended daily intake is 0.5 to 1.0 grams of protein per pound of body weight. This is also the recommendation for humans. Using the example above where a horse is being fed a 14% protein mix with alfalfa meal as the protein source, it was determined that the horse would receive and absorb 0.07 pounds of protein for every pound of mix fed. Let’s convert 0.07 pounds to grams. If 1 pound = 454 grams then 0.07 pound = x grams (1/454 = 0.07/x, x = 454 * 0.07, x = 31.78 grams). If a 1000 pound horse needs 0.5 to 1.0 grams per pound, then the requirement is between 500 and 1000 grams of protein per day. For fun, let’s divide 500 required grams by the 32 grams he is getting in 1 pound of mix. The minimum pounds of mix needed to meet this requirement would then be 500 / 32 = 15.6 pounds of mix per day. BUT HOLD ON! Does the alfalfa protein have ALL the amino acids the horse need? No it doesn’t.

Why Protein Loss Occurs In Horses Today

It is obvious that a horse that doesn’t get fed enough protein will become protein deficient. More importantly, even if a horse is fed “enough” protein by calculations, they may not be ingesting enough of the essential amino acids, especially the 3 limiting amino acids (see fact 5 above). Unfortunately there is no test available to determine if your horses are getting every amino acid they need. Instead, we just need to look at some of the diseases they suffer from when they don’t have enough protein. Here is a partial list and some of these diseases may be directly from an absence of a protein and others may be from a cascade of events of which protein deficiency is only a part of the disease.

  • Poor hair coat (unthrifty, scaly, rough, lack luster)
  • Skin conditions (rain rot, scratches, ventral midline dermatitis, the crud, itchy horse)
  • Poor hooves (cracks, splay, dropped sole, laminitis, shelly, thrush)
  • Poor top line (prominent withers, prominent back bone, sway back, kissing spine)
  • Lame (all connective tissue causes including suspensory desmitis, bowed tendons, dropped fetlocks, joint dysfunction, muscle soreness, separation of the coffin bone from the hoof)
  • Immune dysfunction (increased cortisol or Cushing’s, neurotransmitter deficiency, gut problems, parasite load)
  • Cancer (canker, melanoma, sarcoid, pithiosis or summer sores)

If your horse has any of these issues then your horse may have a protein deficiency. Let’s look at some of the reasons for this.

1) Your horse is being fed a limited amount of a variety of proteins. This leads to a overall deficiency in materials to build all the needed proteins. Remember the idea that a deficiency of one amino acid is equal to a deficiency in all amino acids (fact 5 above). This leads to a deficiency of every amino acid and subsequently a deficiency of every protein made with the limiting amino acid.

2) Your horse is being fed a proton pump inhibitor which are basically anti-ulcer medications (omeprazole, Prilosec, Peptid AC) . These types of drugs will make the pH of the stomach less acidic which prevents the breakdown of the large proteins into smaller peptides and smaller amino acids. This sends the proteins down the gut in their intact form which is indigestible. The result is the same as not feeding the horse protein and a deficiency occurs.

3) Your horse has an inflamed gut with an altered gut bacteria (microbiome). This will lead to an inefficient absorption of all nutrients including any amino acids that may get to this point. Again the result is a decreased uptake of the materials to build proteins within the body.

4) Your horse is overwhelmed with a disease or stress or both. These will increase the consumption of proteins. This includes over-working the musculoskeletal systems which leads to connective tissue breakdown. It also includes a load of parasites in the environment that the horse’s immune system is desperately fighting consuming a lot of protein as it does so. Hence the poor hair coat of a parasite ridden horse.

5) Your horse is on other medications including antibacterials and antimicrobials. These alter the good gut bacteria which in turn decreases the absorption of amino acids. In addition, the causes for which these drugs are being used are also increasing the consumption of proteins.

6) Your horse is starving either because there is no food available or he is being fed in a carbohydrate dependent fashion. The body now has no choice but to consume existing muscle along the top line or, in horses over 30 years, from the cheek muscles. The result is a poor top line, a horse that looks old, sway back or if still working, kissing spine injuries from back muscles unable to support the spine in ridden and athletic endeavors.


Proteins are essential but are often overlooked by horse owners because they seem “too complicated” to understand. They are not. Simply feed your horse like a horse by allowing it to graze on a variety of pastures.

1) If no pasture or poor pasture or pasture made of only 1 type of grass is available, add plenty of grass hay plus some legume hay. If all looks good and the horse is not being used, then add about ½ pound of a grain free protein supplement per day for a 1000 to 1400 pound horse.

2) If working or if you believe there is a protein deficiency, add 1 pound of a grain free protein supplement (soy and whey mix) per 1000 to 1400 pound horse per day. When the horse looks great (hair coat, top line, hooves, lameness, disease) then reduce the amount being fed by ½.

3) Eliminate sugars from grain, byproducts, treats, and fruit (unless in season and available where you live). If you can’t find a protein supplement without grain, use one that has only 1 grain and watch for signs of grain intolerance.

There - you now know about the importance of protein and realize that most horses kept by humans are slightly to severely deficient in protein. Couple this to what you have already learned and then join me for the next blog.

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