Feed Test Interpretation

 Knowledge Nuggets | Fact Sheets | Research

Knowledge Nuggets

  • Crude Protein (CP) - is measured by determining the nitrogen content of the forage and calculated using the formula: CP = % N x 6.25. Crude protein will include both true protein and non-protein nitrogen.
  • Unavailable Protein – is protein that is unavailable to the ruminant resulting from excessive heating of forage or silage during storage. Feed test reports will not indicate unavailable protein unless a separate analysis is requested. It can be reported as ADF-N protein, ADF-CP, bound protein, or insoluble protein.
  • Available Protein is the difference between crude protein and unavailable protein. All forages have some unavailable protein
  • Acid Detergent Fiber (ADF) measures cellulose and lignin, the least digestible fibre portions of the forage. ADF value influences forage digestibility and voluntary intake of the forage. As ADF increases, energy and protein levels decline, digestibility and intake decreases. Many of the calculated energy values appearing on the forage reports are generated using ADF values.
  • Neutral Detergent Fiber (NDF) - The NDF value is the total cell wall, which is comprised of the ADF fraction plus hemi cellulose, tannins, cutins, silica and lignin. These values are important in ration formulation because they influence feed passage rates. As NDF percentages increase, dry matter intake will generally decrease.
  • Crude Fiber (CF) – measures the indigestible portion of the plant material.
  • Lignin content of plant material increases with maturity. It is the prime factor influencing the digestibility of the plant cell wall. As lignin increases, digestibility, intake, and animal performance usually decrease
  • As Received or As Fed Basis feed nutrient values express the amount of nutrients with “moisture included”. Because of the dilution with water, the values will be lower than the dry basis column.
  • Dry Basis Values give the nutrient information with the water removed. This allows comparisons to be made between forages. Multiplying the value by the percent dry matter can make conversion to the as-received or as-fed value.
  • Net Energy-Lactation, Net Energy-Maintenance, and Net Energy-Gain and TDN values, are calculated from ADF values. As the percent ADF in the forage increases, the net energy values will decrease.
  • Relative Feed Value provides a standard method to compare one feed against another. A forage with ADF of 41 percent and NDF of 53 percent has an index of 100. Relative feed values increase as fibre components decrease. Forages with a relative feed value of 80 to 100 can be fed to pregnant beef cows.
Fact Sheets

Interpreting Forage Analysis - available in PDF format only

Know Your Feed Terms

Definitions of Feed Manufacturing and Livestock Nutrition Terms


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This document is maintained by Mary Ann Nelson.
This information published to the web on March 20, 2003.
Last Reviewed/Revised on March 15, 2017.

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