More myth and misunderstanding surrounds protein than any other nutritional concern. Conversely, the only thing many people can tell you about what they feed is protein content. Protein is widely considered to make a feed too “rich,” even harmful, but protein is the most important ingredient in your horse’s body. It is especially important for hard-working performance horses.
However, just increasing the quantity of dietary protein is expensive and wasteful — much of it will not be efficiently used by the horse. Instead, you should improve the quality of the protein, which allows you to feed less and get equivalent, if not better, effects.
Quality involves several factors, including the number of essential amino acids it contains and at what levels, how “complete” the protein is, and its digestibility.
Proteins are made of amino acids. Essential amino acids are those that the body can’t synthesize itself, making them essential in the diet.
The only essential amino acid documented for horses is lysine. The growing horse requires about 0.6 to 0.7% lysine in the diet, mature horses around 0.4%.
However, there are nine other essential amino acids (really 12, but some are considered as groups) identified for humans and the pig (the animal considered to have a digestive tract most similar to a horse’s). Some of these are “conditionally essential,” meaning demands like heavy exertion can exceed the body’s ability to synthesize them.
Complete Or Incomplete
A complete protein source contains all of the essential amino acids. There are few of these: soy, milk products, meats and eggs. However, the designation of “complete” doesn’t mean one of these can be used as the only protein source in the diet.
To be a perfect complete protein source, it would have to provide the essential amino acids in the precise amount needed by the animal. The only perfect complete protein source for any animal is its mother’s milk. However, since amino-acid needs for growth differ from those of the adult, and amino-acid needs for exercise differ from those for maintenance, we’re still left without a perfect source for mature, working animals.
Whey vs. Soy
Our chart (see end of story) compares protein sources and the levels of some key essential amino acids in them (glutamic acid isn’t normally essential, but we’ve included it because it can be conditionally essential in a hard-working athlete). The amino-acid profiles are from the USDA.
The chart shows why we believe whey is a higher quality protein source than traditional soy found in most equine diets.
Whey has a higher biological value and is higher in specific beneficial amino acids. Raw, sweet whey has only about half the level of the BCAAs or branched-chain amino acids (leucine, isoleucine, valine) and lysine, as a percentage, as raw mature soybeans. However, by the time the soybean is processed, especially if it is exposed to heat by processing, such as making it into pellets, this picture can change dramatically. It gets even worse if the soybean is cooked and older, which further reduces the amino-acid level.
With whey, you start with a stable protein source with a known digestibility of nearly 100%. It doesn’t matter how good the protein looks on paper if the amino acids don’t get into the body efficiently. Whey is a more reliable and more concentrated essential amino-acid source that effectively raises the horse’s dietary protein level without waste (see sidebar on performance horses).
When you feed a lot of extra protein without paying attention to its quality, the body metabolizes the amino acids it doesn’t need into urea/ammonia (think smelly stall). This is where you get into trouble just throwing protein at the horse with no concern for what you are trying to accomplish. To raise your horse’s dietary protein level efficiently, we recommend using whey instead of a soy-based protein supplement.
You can purchase whey protein concentrates at human health-food stores. We fed Champion Nutrition’s Whey Protein Stack (see our March 2000 issue or www.champion-nutrition.com) for immune-system boosting. We chose Whey Protein Stack as it is a high-quality concentrate at a good price. However, there are many sports-related whey protein products. Prices vary widely, so shop around.