Feed represents the largest operating cost for cattle producers today. To obtain an optimum balance between feed costs and production, feeds must be routinely analyzed, and the results should be used to balance rations and/or supplements. It is possible to use an average book value for standard feeds, but it is important to remember that feeds vary significantly in nutrient profiles from year to year. Variation may be a result of location, maturity and/or other changes in feed management practices.
The first step in obtaining a feed analysis is collecting a good representative sample of that feed. Taking multiple subsamples of feed and mixing them will help ensure you have a representative sample. Additionally, samples of wet feed such as wet by-products and silages should either be shipped the same day they are taken or stored in a cool place prior to shipping to prevent any loses/spoilage. No sample should be set out in the sun for days at a time because heat and sunlight can degrade the sample. Sample bags and instructions on proper lab submission protocols can be obtained from your consultant or the commercial feed lab.
Most commercial laboratories have standard nutrient profiles for forages, grains and total mixed rations. At minimum, we like to analyze feeds for dry matter (DM), protein and energy. Labs will report nutrient values on both a DM and as-is basis. All rations are formulated on a DM basis, therefore, the nutrient levels reported on a DM basis are used. Once we have balanced rations, we can then convert values to an as-is basis (using the DM content of the feed) to determine the actual amount of feed that should be fed daily.
Labs can analyze feeds by two different methodologies: traditional wet chemistry or near infrared reflectance spectroscopy (NIR). NIR is faster and usually more economical; however, NIR results are only as good as the database of wet chemistry results summarized for that feed. Consult with your nutritionist if you have any questions about which analysis is best for the samples you are submitting.
Table 1 provides a list of common nutrients present on lab analysis reports, as well as the common units they are reported in. The following descriptions of each nutrient and their subcategories will help explain the information reported on the feed analysis.
MOISTURE
Dry Matter (DM): Dry matter is the moisture-free content of the sample. The DM portion of feed is made up of protein, fat, fiber, vitamins and minerals. Since moisture (i.e. water) dilutes the concentration of nutrients, it is important to always balance rations on a DM basis.
PROTEIN
Crude Protein (CP): Crude protein is determined by measuring the nitrogen content of a feedstuff, which includes both true protein and non-protein nitrogen. In ruminants, separating out the rumen degradable (RDP)and rumen undegradable (RUP) portion of CP is important. However, most commercial labs do not have the capability to measure RDP correctly, if at all. Therefore, we formulate rations with the lab analysis of CP, and use the RDP and RUP values from the 2016 Nutrient Requirements of Beef Cattle.
Heat Damaged or Insoluble Crude Protein (ICP): Nitrogen that has become cross linked with carbohydrates thus not contributing to either the RDP or RUP supply. The linkage is a result of hays heating when baled and/or stacked at a moisture greater than 20%, or when silage is harvested at less than 65% moisture. Feeds with high ICP are typically discolored and have a distinct sweet odor. When more than 10% of the CP is unavailable, the CP value is adjusted (see ACP below). Note: this only applies to roughages, heat damaged corn cannot accurately be measured.
Available Crude Protein(ACP): CP corrected for ICP. When ICP is greater than 10%, the ACP values are reported. This value is what we use when formulating rations.
FIBER
Crude Fiber (CF): Crude fiber is the traditional measure of fiber, but it is not as valuable as neutral detergent (NDF) and acid detergent fiber (ADF) in determining feeding value of various forages.
Neutral Detergent Fiber (NDF): Measures the structural components of the plant cell wall. NDF helps predict voluntary intake because it indicates the amount of bulk or fill of a forage. In general, a lower NDF value is desired because as a plant matures NDF increases.
Acid Detergent Fiber (ADF): Measures the least digestible components of a plant, which are cellulose and lignin. ADF values and digestibility are inversely related, therefore forages with low ADF values are usually higher in energy.
ENERGY
Total Digestible Nutrients (TDN): The summation of digestible fiber, protein, lipid and carbohydrate components of a feed or ration. TDN is related to digestible energy and is often calculated based on ADF values. TDN is useful when formulating beef cow rations that are composed of predominately forage. However, in high concentrate rations (i.e. backgrounding and finishing) net energy should be used to formulate and predict animal performance. TDN values typically under predict the feeding value of concentrates relative to forages.
Net Energy (NE): Commonly referred to as net energy for maintenance (NEm), net energy for gain (NEg) and net energy for lactation (NEl). The net energy system separates energy requirements into their fractional components used for tissue maintenance, tissue gain and lactation. To accurately use the NE system, you must carefully predict feed intake.
Ether Extract (EE): The crude fat content of a feed. Fat provides 2.25 times the energy density of carbohydrates.
Relative Feed Value (RFV): A prediction of feeding value that combines estimated intake (NDF) and estimated digestibility (ADF) into a single index. RFV is used to evaluate legume hay. RFV is often used as a benchmark of quality when buying or selling alfalfa hay. RFV is not used for ration formulation.
Relative Forage Quality (RFQ): Like RFV, RFQ combines predicted intake (NDF) and digestibility (ADF). However, RFQ differs from RFV because it is based on estimates of forage intake and digestibility determined by incubating the feedstuff with rumen microorganisms in a simulated digestion. Therefore, it is a more accurate predictor of forage value than RFV. Neither RFV nor RFQ are used in ration formulation.
As always, if you have questions on how to interpret your feed analysis results or would like to get some feed samples taken please contact a consultant at GPLC!
