Tips for Interpreting Forage Analysis

Tips for Interpreting Forage Analysis

By Dr. Megan Van Emon, MSU Extension Beef Cattle Specialist

Having your hay and pasture quality analyzed prior to feeding or turnout is one of the most important and effective tools for cattle feeding management. Forage analysis allows for more precise feeding of supplements and other feedstuffs to meet requirements throughout the year. Forage analysis becomes especially important during drought and the possibility of limited forage intake while on grass. Therefore, accurately interpreting that forage analysis is crucial.

As Received Basis

These values represent the content of nutrients with the moisture included. Due to dilution, these values are lower than those in the dry matter basis column. These values can be converted to a dry matter basis by dividing the as received values by the percentage dry matter.

Dry Matter Basis

The values in this column give the nutrient profile after the water is removed. These values will be greater than those in the “as received” column. The removal of water allows for direct comparisons to be made between feed ingredients. The dry matter basis gives the best indication of the nutritive value of the feedstuff because we report animal requirements on a dry matter basis. Dry matter values can be converted to an as received basis by multiplying the dry matter value by the percentage dry matter.

Crude Protein (CP)

Labs measure the Nitrogen (N) content of the forage in order to estimate CP (% CP = % N × 6.25). Crude protein will include non-protein nitrogen and true protein. Crude protein provides the total protein within the forage and does not indicate if any heat damage has occurred, which could alter the availability of the protein.

Acid Detergent Fiber (ADF)

The acid detergent fiber encompasses the cellulose and lignin portions of the cell wall. This number is crucial in determining the ability of the animal to digest the forage. As ADF increases, forage digestibility decreases.

Neutral Detergent Fiber (NDF)

The NDF includes the ADF portion plus hemicellulose. The NDF value is important for determining forage dry matter intake. As NDF increases in the forage, dry matter intake decreases.

Total Digestible Nutrients (TDN)

This is the sum of the digestible fiber, protein, lipid, and carbohydrate components of the forage. In most laboratory analyses, TDN is usually calculated based on ADF and NDF and can vary by region and diet type. Typically, high quality forages range from 50 to 60% TDN and low quality forages range from 40 to 50% TDN. Using TDN in ration calculations is best for rations that are primarily forage. The net energy system should be used in diets that include high concentrations of grain because TDN tends to underestimate the feeding value of concentrate relative to forage.

Net Energy of Lactation (NEl), Net Energy of Maintenance (NEm), and Net Energy of Gain (NEg)

The Net Energy system accounts for the energy losses from digestion of feeds and forages. Net energy estimates the portion of energy in a forage that is useable to the animal to meet the needs of body maintenance and production. Net energy is partitioned into the net energy of maintenance (no body weight gain or loss), net energy of lactation (milk production), and net energy of gain (body weight gain). The net energy system should be used for diets containing high concentrations of concentrates. Net energy values are usually calculated from TDN values, which are calculated from ADF. Therefore, as ADF increases in the forage, net energy values will decrease.

Ash

This represents the total mineral content of the forage and typically ranges from 3 to 12% on a dry matter basis. Grains and concentrations usually contain range from 1 to 4% ash. Excessive amounts of ash indicate soil contamination.

Other analyses can also be conducted, such as nitrates, molds, yeasts, and mycotoxins, and individual minerals. These analyses are not typically included in a standard test and must be requested at an additional cost.