Protein - What are the Best Sources?

By Juliet M. Getty, Ph.D.

Protein. The neglected nutrient.  With so much attention being paid to low starch diets, horse owners are turning to fat to provide additional calories.

Carbohydrates and fats are very important, don’t get me wrong. But do you know if your horse’s protein needs are met, as well?

Protein provides amino acids, building blocks used to create body proteins, such as:

  • Heart, lungs, liver, and other vital organs
  • Skeletal muscles
  • Blood proteins
  • Skin, hair, and hooves
  • Bones
  • Eyes
  • Connective tissue
  • Enzymes
  • Antibodies
  • Red blood cells

If protein intake is inadequate, one or more of these bodily tissues will suffer. Since your horse’s priority is to stay alive, available amino acids will first be used to feed vital tissues. If there are any left over, fewer life-supporting tissues will be tended to – things like skin, hair, hooves, and eyes. The immune system may also take a back seat, leading to a higher susceptibility to infections or the development of allergies. For these reasons, protein has to not only be in adequate quantity, but also in adequate quality. A high-quality protein source will have all ten essential amino acids in proper proportion to one another. There are 22 amino acids, 10 of which either cannot be produced by your horse or cannot be produced in adequate quantity; therefore, they must be in his diet. If one or more essential amino acids are not available, protein synthesis cannot occur.  Animal proteins such as eggs, meat, and fish do meet the definition of high quality, but horses are herbivorous. Consequently, they must rely on eating plant protein sources that complement each other to create a balanced proportion of amino acids.

Horses in a wild environment would eat a variety of feedstuffs – grasses, grains, fruits, flowers, leaves, legumes, and more – creating a balanced diet.  For most domesticated horses, this is not the case. They are most likely fed the same thing day in and day out, making it especially important that all nutrients, including protein, are fed in adequate quantity. This means that a diet of strictly one type of grass will not meet your horse’s amino acid requirement – others feedstuffs must be included.  

Getting enough protein is generally not the issue. Most grass hay, for example, has 8 to 10 percent crude protein (measure of nitrogen found in protein). Twenty five pounds per day will provide at least 900 grams, the minimum requirement for the average, healthy adult, 1100 lb (500 kg) horse, exercised lightly. Add to this other protein sources and the grams requirement is easily met.  Here are the crude protein levels of some common feedstuffs:




Crude Protein in Commonly Fed Feedstuffs*


Forages and fibrous feeds

Percent Range

Alfalfa (hay, cubes or pellets)


Beet pulp


Grass hay, warm season (Bermuda, Coastal, Tifton)


Grass hay, cool season (brome, orchardgrass, timothy, fescue)


Oat hay


Rice bran




Soybean hulls


Wheat bran


Wheat hay


Wheat middlings



Percent Range



Canola meal




Flaxseed meal




Soybean meal


Sunflower meal




 *Values obtained from the National Research Council, 2006 and Equi-Analytical Labs

Keep in mind that the above values can vary dramatically based on growing conditions, and are offered as general guidelines. Notice, for example, that cool season grasses can range from 5 to 15 percent protein. This is why is it so important to analyze your specific hay to take the guesswork out of evaluating your horse’s diet.

Commercial feeds

Crude protein levels found in commercially fortified feeds can vary dramatically.  Avoid high protein feeds unless you have a horse with a special need for extra protein, such as growth, pregnancy/lactation, performance, surgery recovery, or injury. For the healthy adult horse, I prefer that the overall diet contains approximately 14% crude protein from a variety of protein sources.


Your grass hay tests at 10% crude protein and you feed 25 lbs per day. You also feed 4 lbs per day of a 14% commercial feed. Is your horse getting 14% protein overall?

  • Grass hay:  25 lbs X 454 grams/lb X .10 = 1135 grams protein
  • Commercial feed: 4 lbs X 454 grams/lb X .14 = 254 grams protein

Total grams of protein in 29 lbs (same as 13166 grams)** of feed:  1135 + 254 = 1389 grams. 

Percent: 1389/13166 X 100 = 10.55%

You are far away from providing the 14% crude protein desired.  Let’s replace 10 lbs of grass hay with 10 lbs of alfalfa at 20% protein…

  • Grass hay: 15 lbs X 454 grams/lb X .10 = 681 grams protein
  • Commercial feed: 4 lbs X 454 grams/lb X .14 = 254 grams protein
  • Alfalfa: 10 lbs X 454 grams/lb X .20 = 908 grams protein

Total grams of protein in 29 lbs (with added alfalfa):  681 + 254 + 908 = 1843 grams

Percent: 1843/13166 X 100 = 14%

Bottom line

Protein needs to be fed in large enough quantity and at a decent level of quality to provide the amino acid pool necessary to keep body tissues healthy. To ensure both of these, feed several protein feedstuffs, or check for variety on your commercial feed’s list of ingredients. Items such as alfalfa meal, soybean meal, beet pulp, distiller’s grains, brans, and flaxseed meal – all add up to a high quality protein. Plenty of grass forage (pasture and/or hay) fed free-choice, along with approximately 30% as a legume (typically alfalfa) -- depending on your horse’s weight and condition – and your horse will have all the building blocks needed to maintain all of the necessary body proteins.  

** To convert pounds to grams, multiply pounds by 454 grams/lb.


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