“What are the signs, symptoms, and treatments of protein deficiency?”

By Suzie Middlebrook, B.Sc., Cavalor Nutrition Specialist

It doesn’t matter if your horse is a top level competitor, a broodmare, or just a pasture ornament, protein is important to all horses. In contrast to popular thought, protein is rarely utilized as a form of energy except in cases of starvation when the horse has to resort to metabolizing its own muscle. Instead, protein is used to build and repair nearly all the structures in the body. Protein makes up everything from muscles and joints to vital organs such as the intestines, kidneys, and lungs. These structures and others may be damaged due to exertion or stress. For example, when a horse lands off a jump or takes a funny step on the trail, there may be small tears in the tendons or ligaments that need repair. The body will use the protein from its diet to heal these small injuries. If the diet does not contain a sufficient amount of protein, then the horse will be forced to prioritize what structures are repaired first. So if the heart also suffered some small amount of damage, then the body may begin to breakdown muscle, tendons, or ligaments to repair the injured vital organ.

Just like many other nutrients, there are different types of proteins, called “amino acids,” which must be included in the diet. Amino acids are the basic components of a protein. Hundreds of amino acids must be bound together in a string-like formation to make up a single protein, similar to the beads of a necklace. There are twenty different amino acids that are divided into two groups: essential and nonessential. Essential amino acids, such as lysine, arginine, and phenylalanine, are amino acids that must be consumed by the horse since the horse is unable to synthesize them. In contrast, nonessential amino acids can be produced by the horse, making these amino acids not critical parts of the horse’s diet as long as the total protein content of the diet is sufficient. Some examples of nonessential amino acids would be cysteine, proline, and glutamine.

If one amino acid was determined to be the most important for horses, it would be lysine. Lysine is considered to be the “first limiting amino acid.” More simply put, if the horse is going to be deficient in an amino acid, it would most likely be lysine. Conversely, if the horse is receiving an appropriate amount of lysine, then the horse should be receiving adequate amounts of the various essential amino acids. It is still possible that a horse may not ingest sufficient amounts of the other amino acids due to the protein quality, not amount, of their forage or grain. For example, while alfalfa is high in both crude protein and lysine, it is comparatively low in the essential amino acids methionine, threonine, histidine, and phenylalanine. If a horse was relying on alfalfa for its primary source of amino acids, the horse may still be considered protein deficient even if the total daily crude protein and lysine requirements are met.

A horse with subpar amino acid intake will often display an under muscled topline and a large belly. These horses are usually described as being “easy keepers” since they maintain their “hay belly” even on only a modest amount of grain and forage while being in substantial work. In truth, these horses are being deprived of a high quality protein source with proper amino acid ratios. Some other effects of an unsuitable amino acid ratio would be an increased chance of injury, compromised immune system, slower muscle recovery, muscle soreness, and reduced feed efficiency due to the compromised lining of the intestines. All these factors combined can dramatically affect the horse’s overall level of performance and wellbeing.

When a horse is suspected of a protein deficiency, it should be given a complete grain with relatively high protein content of adequate quality, such as Cavalor® Strucomix Senior or Cavalor® Perfomix. Both of these feeds are specifically designed with the ideal protein ratio in mind to best meet the needs of the horse. These horses also may benefit from less forage to address any calorie surplus that may occur with an increased grain ration. On the supplement side of things, one may also consider using Cavalor® Muscle Force which is a blend of high quality protein sources in conjunction with the trace minerals critical for protein synthesis, such as magnesium, zinc, and manganese.

Ball, RO, KL Urschel, and PB Pencharz. “Nutritional consequences of interspecies differences in arginine and lysine metabolism.” Journal of Nutrition. 2007; 137(6 Sup. 2): 1626S-1641S.

Harper, F. 2009. “Protein in Horse Diets: The Balancing Act.” Department of Animal Science, University of Tennessee. Knoxville, Tennessee.

Metges, CC. “Contribution of microbial amino acids to amino acid homeostasis of the host.” Journal of Nutrition. 2000; 130 (7): 1857S-64S.

National Research Council. Nutrient Requirements of Horses: Sixth Revised Edition. Washington, DC: The National Academies Press, 2007.