Assessing Protein Levels in Horse Feeds

Feed companies calculate the crude protein value of a feed based on a chemical analysis of the overall nitrogen content of a feed.

Photo: Erica Larson, News Editor

Editor's Note: Learn more about protein in Understanding Protein in Horses' Diets.

Most horse owners determine a horse feed’s protein level by looking at the percentage value on the feed tag under “crude protein.” But the crude protein numbers can be deceptive. They do not really reflect either the overall quality of the protein (which can only be determined by the amino acid profile), or the amount of protein from that feed that the horse can digest and use.

The crude protein (CP) value is based on the overall nitrogen content of a feed, and not all of the nitrogen in a feed sample is necessarily protein-bound. Nitrogen also can be found in purines, creatinine, ammonium salts, and nucleic acids, all of which might be in a feed sample. In cattle feeds, a common non-protein source of nitrogen is urea, which is added to help cattle synthesize their own proteins when the nitrogen is made available in their guts. Urea also can be found in some horse feeds, but horses are not equipped to use it the way cattle are. It does no harm but also has no benefit.

Feed companies calculate the crude protein value of a feed based on a chemical analysis of the overall nitrogen content of a feed. Based on the idea that most proteins contain about 16% nitrogen, plus or minus 2%, the nitrogen content of a feed is divided by 0.16 (or multiplied by 6.25 for the same result) to arrive at the crude protein value. For example, if you know a feed has a nitrogen content of 1.6%, the crude protein of that product would be 10%.

The possibility of non-protein-bound nitrogen sources in the feed makes the CP level, at best, an estimate of what the horse actually can digest and use. As a rule, you can estimate that most grain products are somewhere between 2% to 5% lower in digestible protein (DP) than the CP numbers indicate. A product described as being 14% crude protein probably would deliver 9% to 12% DP. The difference is more dramatic with hay. Depending on the stage of bloom in which the hay was cut, sometimes only about 50% of the protein might be digestible.

The availability of amino acids in a grain ration can be adversely affected by denaturing or oxidation as a result of long storage (particularly in warm conditions or bright sunlight) or improper heating (as can sometimes occur during a pelleting or extruding process). Inadequate drying of a heated feed, prior to storage, also can reduce the protein digestibility. Some feed companies anticipate these problems with feeds that undergo heat processing, and add supplemental levels of lysine (and sometimes other amino acids as well) to compensate.

In a future article, we'll examine how much protein your horse needs in his diet, and what problems excesses and deficiencies might cause.

About the Author

Karen Briggs

Karen Briggs is the author of six books, including the recently updated Understanding Equine Nutrition as well as Understanding The Pony, both published by Eclipse Press. She's written a few thousand articles on subjects ranging from guttural pouch infections to how to compost your manure. She is also a Canadian certified riding coach, an equine nutritionist, and works in media relations for the harness racing industry. She lives with her band of off-the-track Thoroughbreds on a farm near Guelph, Ontario, and dabbles in eventing.

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