Feed testing (Animal Science Update)
(Editor’s note: Michael Westendorf is with Rutgers University’s School of Environmental and Biological Sciences.)
Nutrient content is also influenced by maturity at harvest, weather conditions and storage environment. Optimal levels of production will be reached only when feeds are tested and diets are balanced for production.
Testing is particularly important for animals in a highly productive condition such as lactation, growth, or exercise. Diets should be balanced for energy, protein (soluble, rumen degradable, and rumen undegradable), Acid Detergent Fiber or ADF, Neutral Detergent Fiber or NDF, Non-Structural Carbohydrates or NSC, minerals and Vitamins. When feeding a ruminant (cattle, sheep) it is also important to remember the importance of feeding the bacteria and protozoa which dwell in the rumen.
These make it possible for ruminants to digest high-fiber feeds which other animals cannot digest. Some of the terms on a feed analysis sheet are specific to different classes of animals.
There are several places to send feed for testing. Many feed companies provide testing services when you buy their feeds. In addition, there are commercial laboratories which will analyze feedstuffs for nutrient content. What do the terms in a feed analysis mean?
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. Nutrient requirements are usually presented on a DM basis.
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, but for a dairy cattle is also essential for milk production. Unfortunately, CP does not distinguish the nitrogen contained as “amino acid nitrogen” or “non-protein nitrogen.” Because of this, there are other measurements which will describe different protein fractions in feed. 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 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 in order to maintain adequate microbial growth.
Undegradable Protein is also referred to as bypass protein. It is the 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 fraction which is degraded in the rumen rapidly.
Soluble protein is converted into ammonia in the rumen within a short time after being ingested. The remainder of the degradable fraction may take hours to be broken down. Soluble protein also contains non-protein nitrogen.
High producing ruminants (cattle, sheep) 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.
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.
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. ADF and NDF must be balanced properly.
Too little fiber will result in improper rumen functioning and off-feed, displaced abomasum and foot problems. Too much fiber will mean decreased diet digestibility, decreased feed intake and decreased milk production. Minimum target levels of ADF and NDF 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 DIP and soluble protein to ensure proper microbial growth in the rumen.
If NSC is inadequate, the DIP and soluble protein will not be utilized to the greatest extent possible.
Energy Values are measured as Total Digestible Nutrients (TDN) or as 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. Units of NE are expressed as megacalories or mcal/lb.
There will also be mineral information expressed on a feed analysis. It is essential to maintain adequate levels of calcium, phosphorus, potassium, sodium magnesium and other minerals and vitamins when balancing a ration.
With the help of your feed company, a consulting nutritionist, or an Extension agent, balance diets for nutrient content. Prepare now and keep in mind some of the guidelines present here and you will be on target.
Two laboratories that conducts feed and forage testing are the DairyOne Forage Testing Laboratory located in Ithaca, N.Y .and Cumberland Valley Analytical Services in Waynesboro, Pa..
Information about their services can be found at: http://dairyone.com/analytical-services/feed-and-forage/about-forage/ or https://www.foragelab.com/.
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