How Long Do I Need To Feed Soybean Meal To My Horses?

Answering this question requires a review of the 2 causes of chronic protein deficiency in horses.  The first cause is the absence of a complete variety of amino acids in the diet and / or not feeding enough “high quality” protein. The second cause is the continuous resorption of amino acids due to a high level of carbohydrates (sugars) in the diet every day of the year.  The short answer then is this: feed a variety of seasonal ground plants throughout the year AND prevent the conversion of the proteins in the horse to sugar.  If you achieve these 2 things then you can stop feeding soybean meal (SBM).  Now to review the two causes of chronic protein deficiency in horses.

Cause 1

All proteins are made from the combination of only 20 amino acids (AA’s).  There are 1 to 3 billion proteins in 1 cell of our body yet they are all made of only these 20 amino acids.  Like the 26 letters of our American alphabet making the tens of thousands of words in the dictionary, the amino acids are placed in a certain order and amount to make a viable protein.  If you consider a dictionary missing 1 or more letters worthless to writing words then you will understand that missing 1 or 2 amino acids will make a mess of things in the body.  Proteins can not be made without the missing AA’s.  Luckily the horse can make 10 of these but the other 10 must be ingested in the food they eat.  These ten are called the Essential Amino Acids (EAA’s).

In keeping horses today, most horses are limited to basically a mono-grass pasture.  There are 1 or maybe 2 primary plants within the fenced area and the horse, who normally migrates from one area to another covering a thousand miles or more in a year, now only gets what is offered within the fencing.  All forages (pastures and hays) are only “good quality” proteins meaning they do not have a full compliment of all essential amino acids.  Feeding hay is feeding last summer’s pastures and also are only a source of “good quality” proteins with not all the EAA’s.  

Feeding any feed (grains, byproducts, senior feeds, balancers) will provide only a small amount of protein.  If the tag says 14% crude protein then only 14% of what you feed is protein.  In math terms, if you feed 454 grams (1 pound) of a 14% feed then you are feeding 64 grams of crude protein.  Is this enough?  The target is 0.5 to 1.0 gram of protein per pound of body weight.  A 1200 pound horse will need 600 to 1200 grams of protein.  The pasture and hay will provide about 20 pounds of about 10% protein (average) which is 2 pounds or 908 grams.  908 plus 64 = 972g of protein.  Should this be enough?  Unfortunately not because crude protein is not what the horse actually gets inside to use because not all of the protein is digested and absorbed.  For all grasses and legumes, the available absorption is about 50% so the 972g becomes 486g – well below the minimum target of 600g.

It is vitally important to remember that all grass and legumes of mono-grass pasture and mono-grass hay do not have all the EAA’s.  Therefore not only are they not getting enough protein in a day from our pastures and hay but the quality is only “good” – they are getting an incomplete amount of amino acids.  Feeding pasture as we know it today and supplementing with hay every moment of the day will never get the total amount of EAA’s needed to counter the loss described in Cause 2 below.  The only solution is to offer a broad variety of ground plants from wild fields throughout the year.  I can’t see this happening in the United States for most horse owners today where most horses live in suburban areas.  

Cause 2

There is a continual loss of body protein occurring daily as proteins are normally destroyed by design and then rebuilt.  For example, all muscles are proteins and in humans are replaced every 6 years.  Neurotransmitters are proteins with a lifetime measured in less than a second. There is an effective recycling program that returns the AA’s to the protein building sites in the cells to be reused.  After all they are just letters of words – a “T” can be used in any word needing a “T.” I can take the “T” from “Take” and use it again in “Doc T.”

Why then do our elders suffer from muscle loss (sarcopenia) with the secondary effect of falling?  This leads to the death of most of our loved ones from secondary problems of falling.  The same is true in horses with lost top lines, breakdown of ligaments and tendons, development of neurodegenerative diseases and other protein loss related conditions.  These are all signs of chronic protein deficiency.

In a nutshell, when sugar is offered every day in excess of the needs of the horse, the cell slows down from exhaustion.  Sugar comes in many forms including the starch in grains, grass, hay, treats, fruits and roots (apples and carrots).  The primary purpose of ingesting sugar is to replenish glycogen (how animals store glucose) with excess being converted into body fat for the upcoming winter cold.  Glucose stored as glycogen is used for immediate use as a fuel to run, play, and survive an attack by a hungry lion.  Once the glycogen stores have been restored, the next purpose of glucose is for immediate on-demand fuel for just living, breathing, digestion, heart beats, etc.  Ingested sugar in excess of daily use and glycogen replenishment is converted into body fat.  This is good news as winter approaches and sugar is no longer available in the wild.  Horses and all other animals want to stay warm as well as have an alternative source of fuel when there is no more pasture and fruit to eat.

The absence of sugar in the diet forces the horse to convert body fat into fuel but it also signals the cells to do house cleaning.  This is very important to their continued health and collectively, the overall health of the horse.  However horse owners have a different plan.  With excuses that their horse works really hard or that they just love to feed the horses, owners continue to feed the horse starch in the form of grains and hay.  This leads to cellular exhaustion due to the continuous use of glucose which is really a low grade fuel.  Let me explain.

Inside almost every cell of the body are parts called the mitochondria which are the consumer of the fuels glucose (sugar) and ketone bodies (fat) and the producer of energy that keep the cells alive and functioning.  Glucose is like cheap fuel in your Ferrari.  Eventually, without maintenance, your underperforming sports car will sputter to a stop.  Ketone bodies, as another cellular fuel, provide your cells with 20 to 28 times more energy than glucose and produces no pollutants (called free radicals).  Feeding sugar every day in excess of the needs of the horse will lead to exhaustion of the mitochondria.  This is one of the main reasons for resisting the efforts of insulin in delivering glucose to cells.  Also known as IR (insulin resistance), the excess glucose is now stored as body fat as the cell grows weaker from not accepting the glucose.  The cell just can’t use it even though it needs it.  So the brain, in the effort to save the life of the person or horse, converts the readily available amino acids in the recycling program into ……… glucose!  This is called gluconeogenesis and this eventually leads to chronic protein deficiency.

So when do I stop feeding SBM?

The answer to this often asked question is when you can 1) increase the availability of a variety of amino acids in a natural diet and 2) decrease and eliminate the conversion of amino acids into glucose.

Originally I said that 1 to 2 years of feeding SBM should be enough.  This was based on so many people afraid of feeding SBM as a protein source for their horses.  Saying it was temporary seemed to help people make the plunge.  After a year or two with positive results, most horse owners proclaimed that they would never stop feeding SBM.  But the worry of long term use or feeding protein in excess of needs seems to worries owners.  It should not.  There is no evidence in the literature or in the experiences of those using it and I have used it since I started with horses in 1973.  On the other hand, there is plenty of evidence of chronic protein deficiency in horses and this is ruining horses everywhere.  

There is one important thing to consider when feeding additional protein for replacing lost amino acids.  It doesn’t work when adding sugar in excess of daily needs.  In other words if you add soybean meal WITHOUT REMOVING the excess sugar, the horse will only become fatter.  Here is why.

Feeding 1 gram of protein per pound of body weight per day to humans who are eating about 50 to 100 grams of sugar per day produces muscular development, loss of body fat and a feeling of dietary satisfaction (satiety).  More importantly, the amount of insulin (the hormone that converts sugar into body fat) is LESS THAN the amount of glucagon (the hormone that converts body fat into fuel for cells).  This is known as the I G ratio or written I:G.  Most Americans have an I:G of 4:1. When 1 gram of protein per pound of body weight per day is added to a person with an I:G of 4:1, it causes insulin to spike to an I:G of 70:1.  This can be devastating to those with insulin resistance.  In addition, obesity continues and proteins are never made but are further destroyed by the body.  In fact, the amino acids eaten are converted into glucose before they ever become a protein in the body!  I can only assume this is also true in horses as some who add SBM along with grain, copious amounts of pasture and hay, supplements and treats never see the results where sugar is restricted.  The horse actually gains more body fat.

Sometimes the pasture changes with the season and the starch increases.  This causes the protein they eat to be converted into glucose before it gets a chance to be used for rebuilding.  A sure indication of this is a strong ammonia smell in the urine.  Decreasing the SBM temporarily restores a normal urine odor and increasing it a few weeks later seems to be OK.

Feeding any horse – and each horse – requires keen observations by the owner with adjustments made throughout the year and also between horses.  What works for one may not work the same for others.  In my observations of horses over almost 50 years throughout this country, the appearance of chronic protein deficiency is increasing.  At least now you have an understanding of why and a plan to rebuild your horse back to health.  Feeding SBM for the rest of their lives seems to be part of this plan for most people and their horses.  Or maybe purchasing 50 acres per horse of range land…

Be sure to read all the comments (if any) below before you go.