ISSUE FOCUS FEED & ADDITIVE MAGAZINE March 2026 53 measured total nitrogen content, then converted to a crude protein basis by multiplying by 6.25 (proteins are assumed to contain 16% nitrogen). Sufficient dietary protein (>8% DM) is necessary to facilitate microbial fermentation in forestomach and, if deficient, reduced dry matter intake will result. Crude protein alone is not sufficient to understand how the forage will meet animal protein needs. Unavailable or Bound Protein. Not all nitrogen in a feed is available to microbes or the animal. The portion of crude protein not capable of being degraded by the fermentation microbes or digested by the animal is termed "unavailable protein" or "bound protein." The amount of nitrogen (or crude protein; N x 6.25) that is found in the acid detergent fiber residue is defined as ADIN (nitrogen) or ADIP (protein). This represents the nitrogen in a feed bound to the plant cell wall, which represents heat-damaged protein that is unavailable to both microbes and the animal. The Maillard reaction causes heat damage by covalently linking nitrogen from amino acids to sugar residues of the plant cell wall. Moisture and heat are needed to promote this reaction. Soluble Crude Protein. Soluble Protein measures the total nitrogen in feed (expressed on percent of CP basis) that is potentially soluble in rumen fluid. Soluble protein contains both nonprotein nitrogen (NPN) and true protein compounds. These nitrogen sources are readily used by forestomach microbes for microbial protein production and contribute to a rapid increase in the forestomach ammonia pool. Fiber-fermenting bacteria are absolutely dependent upon the forestomach ammonia pool as their sole source of nitrogen for protein synthesis. Mature grasses may have low soluble protein, which may limit fiber digestion and intake. Fiber Carbohydrates. Carbohydrates make up approximately 70% of the herbivore’s diet and consist of a diverse group of compounds. Typically plant carbohydrates are divided into two groups, fiber and non-fiber carbohydrates, based on their degradability characteristics. Fiber carbohydrates are associated with the rigid plant cell wall and moderately to slowly degraded by the forestomach microbes. Total plant cell wall carbohydrates are determined as neutral detergent fiber (NDF). A subset of NDF is acid detergent fiber (ADF), which measures the cellulose and other indigestible components of the plant cell wall. Both NDF and ADF will increase with plant growth and aging (see Table 1) and are good measures of forage quality when their values are lower. Relationships of NDF and ADF differ depending on whether the plant is a grass or a legume. Degradable Carbohydrates. Those carbohydrates that are found in the plant cell cytoplasm (i.e., storage forms such as starch or sucrose) or the secondary plant cell wall are more readily fermented or digested. One method of defining these carbohydrates is calculating nonfiber carbohydrates (NFC), which comprise all carbohydrates in the plant not accounted for in the NDF fraction. The carbohydrates that make up NFC are quite diverse, as it includes sugars, starches, and fermentable neutral detergent soluble fiber. A directly measured parameter of degradable carbohydrates is nonstructural carbohydrates (NSC). This procedure enzymatically degrades starch and complex sugars into glucose molecules to determine the total sugar and starch content of a feed. Minerals. One of the more important components of feed analysis is determining mineral content. Ash provides a perspective on total mineral content of the feed. Both macrominerals-calcium (Ca), phosphorus (P), magnesium (Mg), potassium (K), and sulfur (S)-and microminerals-iron (Fe), copper (Cu), manganese (Mn), and zinc (Zn)-should be determined by wet chemistry methods. Selenium can be determined at some forage laboratories; however, its cost is high, and one would be better off measuring selenium in blood samples. The use of near-infrared spectroscopy (NIR) method to determine forage/ feed mineral content is not recommended, as mineral values are not adequately quantified. Additionally, molybdenum (Mo) should be requested due to its potential interaction with copper availability. Most labs will be able to measure all these minerals, though sulfur and Mo may require an additional cost.
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