Feeding basics (Animal Science Update)
(Editor’s note: Michael Westendorf is with the School of Environmental and Biological Sciences at Rutgers University.)
When feeding livestock, it is important to first inventory forage and feed supplies.
Following this forages should be tested and diets balanced for nutrient content.
Testing is essential because feed nutrient content will vary from year to year and is always influenced by maturity at harvest, weather conditions, storage environment, etc.
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 lactating dairy cows whose 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 ruminating animal it is important to remember the importance of feeding the bacteria and protozoa which dwell in the rumen, this makes it possible for ruminants to digest high-fiber feeds that single-stomached animals such as swine or poultry cannot digest.
Some of the terms on on a feed analysis sheet are specific to different classes of animals.
There are a number of places to send feeds for testing.
Many feed companies provide testing services when you buy their feeds. In addition, there are commercial laboratories that will analyze feed stuffs 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.
Crude Protein is essential for normal growth, lactation and milk production, and normal body function of all livestock animals.
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.
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 or UP is also referred to as bypass protein.
It is the protein fraction that is resistant to rumen microbial degradation and therefore bypasses the rumen.
Much of it can be digested in the small intestine. Soluble Protein is that protein fraction that is degraded in the rumen very rapidly.
Soluble protein is converted into ammonia in the rumen soon 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 dairy cows require degradable, undegradable, and soluble protein in their diets.
Degradable and soluble protein are required to ensure that adequate protein/nitrogen is present for adequate growth of rumen microorganisms.
This is essential to promote proper functioning of the rumen and to ensure that the maximum amount of fiber is digested in the rumen.
Undegradable protein is also essential; it will be impossible to reach maximum levels of production if some protein does not bypass rumen fermentation.
Balancing diets for dairy cows and other ruminants such as cattle, sheep, and goats will require paying close attention to the levels of all of these different protein fractions in feed stuffs.
Acid Detergent Fiber or ADF is the cell wall portion of a feed stuff 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 reduced milk productiom and weight gain, improper rumen functioning, animals going off-feed, displaced abomasum in dairy cows, and feet problems, etc.
Too much fiber will mean decreased diet digestibility, decreased feed intake, and decreased milk 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 represents 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.
Energy Values, these include total digestible nutrients and Net Energy for ruminants.
These values seen on test reports for forages are determined from ADF using equations developed from digestion trials.
Net Energy is expressed as megacalories per pound of dry matter.
These are estimates of the energy value of a feed used for maintenance, growth, and/or lactation.
The Energy content of feeds should be balanced with an animal’s nutrient requirements.
There will also be mineral information expressed on a feed analysis.
It is essential to maintain adequate levels of calcium, phosphorous, potassium, sodium, magnesium, and other minerals and vitamins when balancing a ration.
When planning ahead, first inventory feed supplies to determine requirements for purchased feed. Second, analyze all feeds to be fed.
Third, 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 presented here and you will be on target.
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