Missouri By Dale Watson
University of Missouri Extension
Questions relating to the interpretation of forage analysis continue to surface when the results of forage samples return from laboratories for formulating rations. The interpretation of these results will assist with ration formulation, reducing feed cost, and improving the daily maintenance of your beef operation.
Interpreting forage analysis isn't difficult, but does require some mathematical calculation when using this information to formulate a ration. Basically the results of a forage analysis can be divided into four different portions. These are protein, fiber, minerals and Relative Feed Value.
The protein portion is based on the nitrogen content of the sample and considers both true protein and non-protein nitrogen. Animals can utilize both these to some degree. Crude protein analysis gives no indication whether any heat damage has occurred to the forage sample. True plant protein is roughly 70% of the protein in fresh forages, 60% of the total in hay forage and lower than 60% in fermented forages. Ruminant animals are able to utilize a portion of both types of protein. Crude protein analysis gives no indication that heat may have reduced the availability of the protein. If excessive heating of forages has occurred an analysis indicating bound protein, insoluble protein or unavailable protein needs to be requested. Knowing the crude protein value of your feeds frequently reduces the cost of rations.
The fiber portion of the analysis is divided into NDF and ADF. The NDF (Neutral Detergent Fiber) portion has been shown to be negative correlated with dry matter intake. This means that as the NDF increases the animals are able to consume less. This is one reason why it is important to harvest the forage at the desirable stage of plant maturity. NDF increases as the advancement of maturity occurs in forages. The ADF (Acid Detergent Portion) of the sample may be considered the most important portion of the analysis. The ADF has nothing to do with the amount of acid in the forage sample. The name of this portion of the analysis comes from the procedure used in determining the amount of cellulose and lignin, or plant structure, in the forage. The higher the portion of ADF the less digestible the forage. This portion of the analysis becomes less digestible as plant development occurs.
The mineral portion of the forage analysis generally indicates the amount of calcium and phosphorus in the forages. Under certain circumstances potassium and magnesium will be included in the analysis. All of these are important and need to be considered when providing a mineral mix to meet the requirements of a complete ration.
The RFV (Relative Feed Value) is an index which contains the important nutritional factors of intake and digestibility. Forage with an ADF of 41% and an NDF value of 53% has an index of 100. Other forages can be compared against this value. Several individuals use this method to determine the value of forages.