Not all protein sources are the same

Jerad Jaborek, Michigan State University Extension

Feedstuffs can vary in their protein and amino acid concentrations, amino acid composition, and site of digestion.

Protein is one of the main macronutrients needed by cattle to survive and grow. As you may know, cattle are ruminants, and therefore have a four-compartment stomach that consists of the rumen, reticulum, omasum, and abomasum. The largest stomach compartment in ruminants is the rumen, which contains a vast diversity of microbes. In the rumen, ingested feedstuffs undergo microbial fermentation and breakdown allowing for nutrient absorption. The rumen microbes also use the dietary carbohydrates and protein consumed by cattle to maintain, grow, and reproduce themselves. As a result, the passage of microbes from the rumen to the lower gastrointestinal tract can provide cattle with two-thirds to three quarters of their protein requirements. We can think about the metabolizable protein requirements of cattle as the sum of rumen degradable protein (RDP), microbial protein (MCP), rumen undegradable protein (RUP), and small contributions from endogenous protein. Rumen degradable protein consists of dietary protein and amino acids, and non-protein nitrogen (NPN), such as urea, that are used by the rumen microbes to reproduce or replicate.  The microbes themselves provide the small intestine with MCP, in addition to dietary RUP that is not degraded by the rumen microbes, endogenous protein from sloughed cells within the digestive tract, and digestive enzymes reaching the small intestine.

Not all protein sources are the same because they are comprised of different concentrations of amino acids. Amino acids are the building blocks of protein, and the animal requires a certain concentration of each amino acid to meet its growth requirement. Therefore, if one amino acid is deficient or limiting, it can . . .

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