What do the terms in a feed analysis mean?

We have had a requests for information about heat damaged hay and forage.   Forage put up too wet will overheat and may result in unavailable protein and hay  unsuitable for ruminant digestion.  A definition of the terms in a feed analysis may be useful.  Some of these terms are useful for ruminant animals (cattle, sheep, goats) only. 

Dry Matter or DM is the part of the forage that is not water.  Because of a large variation in moisture content of feeds, dry matter maintains a base line when expressing feed values and nutrient requirements of the animal.  Feed analysis is usually presented in both an As-Fed (contains moisture) and a DM basis.  Succulent feeds such as silage or green chop are much higher in moisture, and lower in DM, than are feed grains such as corn or barley.

Protein is represented as Crude Protein or CP and is a measure of the nitrogen content of the feed.  CP is essential for normal growth and body function of all animals, it is essential for meat, milk, eggs, and wool production.  Unfortunately, CP does not distinguish the nitrogen contained as “amino acid nitrogen” or “non-protein nitrogen.”  Most CP measured in feed analyses is made up of “amino acid nitrogen.”  Because of this, there are other measurements which will describe different protein fractions or non-protein nitrogen in feed.  Amino acids are the building blocks that make up proteins in meat, milk, eggs, and wool.  Ruminating animals can convert non-protein nitrogen into amino acids through fermentations that occur in the rumen of cattle, sheep, and goats.

Unavailable Protein is calculated from the nitrogen which is bound to the fiber in the feed.  Normally about 1 percent on a dry matter basis is found in this fraction.  Values greater than 1 percent may indicate heat damage.  Often referred to as heat damaged protein.

Degradable Protein is protein that is broken down in the rumen, mainly into ammonia.  Most rumen microbes need ammonia to produce rumen amino acids, maintain adequate microbial growth, and produce proteins that can be used by a ruminating animal for meat, milk, and wool production.

Undegradable Protein is also referred to as bypass protein.  It is protein fraction that is resistant to rumen microbial degradation and therefore bypasses the rumen.  Most of it can be digested in the small intestine.

Soluble Protein is that protein or non-protein nitrogen fraction which is degraded in the rumen rapidly.  Soluble protein is converted into ammonia in the rumen within a short time after being ingested, it is this ammonia that is made into microbial protein. The remainder of the degradable protein fraction may take hours to be broken down.

High producing ruminants require all these forms of protein in their diets.  This is essential to promote proper functioning of the rumen and to ensure that the maximum amount of digestion occurs in the rumen.

Neutral Detergent Fiber or NDF represents all of the cell wall material containing hemicellulose, cellulose and lignin.  NDF has been identified as being highly related to dry matter intake.  The NDF appearing on feed analyses is probably aNDF, referring to amylase treated NDF.  Amylase is an enzyme used to pre-treat the chemical’s used in NDF analysis.  a-NDF is currently the standard treatment used in NDF analysis.

Acid Detergent Fiber or ADF is the cell wall portion of a feedstuff that includes cellulose and lignin as primary components.  The higher the ADF content, the lower the digestibility of the feed stuff.   The most indigestible fractions of feed are the cellulose and lignin components which are often linked.

Acid Detergent Insoluble Nitrogen or ADIN may be referred to in a feed analysis as ADFCP, ADICP, or heat damaged protein (unavailable protein above).   The residue remaining in the ADF fraction is analyzed for nitrogen.   This value is an estimate of the protein that is unavailable to the animal and can be an estimate of overheating of forage that is put up too wet.  Hay put up too wet can undergo a process called enzymatic browning that occurs in the presence of protein and sugars when forage overheats.  The level of heat damage is determined by analyzing the forage for ADIN (Acid Detergent Insoluble Nitrogen).

Too little fiber can result in improper rumen functioning and off feed and other health problems, such as displaced abomasum and foot problems.  Too much fiber will mean decreased diet digestibility, decreased feed intake and decreased production.  Minimum target levels of ADF and NDF for dairy cows are 21 percent and 28 percent of the total diet, respectively.

Non-Structural Carbohydrates or NSC represent contents of plant cells and contains sugars, starches and pectins.  These are carbohydrates which are rapidly fermented in the rumen and utilized by rumen microorganisms.  It is essential to balance NSC with the different protein fractions to ensure proper microbial growth in the rumen.  If NSC is inadequate, the degradable and soluble protein will not be utilized to the greatest extent possible.

Energy Values are measured as Total Digestible Nutrients (TDN) or Net Energy.   Net Energy is expressed as megacalories per pound of dry matter.  There are different NE calculations for maintenance, gain and lactation.  Almost all nutrient requirements used today and in feed testing are expressed as NE.  (Digestible energy is used for horses).  Units of NE are expressed as megacalories or mcal/lb.  These are usually determined by equation based on ADF, NDF, and the protein fractions.