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ARS Home » Midwest Area » Lexington, Kentucky » Forage-animal Production Research » Research » Publications at this Location » Publication #342483

Title: From the Lab Bench: Why depend on a crude measure of protein?

item Aiken, Glen

Submitted to: Cow Country News
Publication Type: Popular Publication
Publication Acceptance Date: 4/11/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: Proteins are the building blocks of the body. Organs and tissues are primarily composed of structural proteins, but enzyme and hormone proteins also are directly involved in constructing and maintaining organs and tissues. Proteins are composed of combinations of 20 different amino acids, which are composed of nitrogen, hydrogen, oxygen and a couple of amino acids contain sulfur. All mammals have an ability to produce 10 of these amino acids, and so are classified as non-essential in the diet. However, the other 10 amino acids cannot be manufactured by animals and, therefore, are classified as diet essential. For cattle and other ruminants, we rely on a measure of crude protein and not measures of these essential amino acids. This is because the amino acids in the diet will first feed the bacteria in the rumen, which will convert these amino acids to produce ammonia and other amino acids that meet the requirements of the bacteria. Then the animal digests the bacteria as a protein source. The livestock industry uses crude protein which essentially is the N percent of the forage or feed times the factor, 6.25, which is average percentage of nitrogen in the amino acids. This information will be helpful to livestock producers that may not understand the definition of crude protein and what it represents.

Technical Abstract: An article was written to discuss what the crude protein value of a feed or forage represents, and justify the relevance of this crude measure of protein. Rumen bacteria digest plant protein and convert the building blocks of protein, amino acids, to those amino acids that meet their needs. Therefore, an analysis of amino acid profiles in the feed or forage will not represent those following ruminal bacteria degradation and available for animal digestion and absorption. Determining nitrogen percentage of a forage and multiplying by 6.25 provides a crude measure of protein that has been successfully used in formulating rations and meeting animal requirements for protein.