The nitrogen content of feed multiplied by a fixed factor, typically 6.25, yields an estimate of the total protein present. This calculation assumes that proteins contain, on average, 16% nitrogen. This value represents the total nitrogenous substances, both true protein and non-protein nitrogen, in a feedstuff. For example, a feed analysis showing 4% nitrogen would be reported as having a calculated total protein content of 25% (4 x 6.25 = 25).
This measurement is fundamental in animal nutrition, providing a quick and relatively inexpensive way to assess the nutritional value of feedstuffs. Livestock require sufficient protein in their diets for growth, maintenance, and reproduction. This assessment helps nutritionists formulate balanced rations that meet these requirements. Historically, this assessment has been a cornerstone of feed analysis, allowing for standardization in the feeding of agricultural animals.