Sarah Flack, Sarah Flack Consulting
Karen Hoffman, USDA Natural Resources Conservation Service
Adapted with permission from: Mendenhall, K. (ed.) 2009. The organic dairy handbook: a comprehensive guide for the transition and beyond. Northeast Organic Farming Association of New York, Inc., Cobleskill, NY. (Available online at: https://www.nofany.org/files/TheOrganicDairyHandbook-2009_copy.pdf, verified 20 Nov 2019).
To ensure that nutrient needs of all of the farm’s animal groups are met, it is important to test forages periodically. The samples submitted should represent what will be fed to the animals. Test the primary stored forages and pasture fed, as they are foundation of the herd’s rations. For alternative crops, request a wet chemistry analysis for a more accurate nutrient composition.
When to Test Forages
There are several situations that warrant forage testing, including the following.
- Before they are fed.
- Throughout the year when a change in the forage or in production is noted.
- From pastures when there are noticeable changes in seasons or weather patterns.
- From purchased forages if the growing or harvesting conditions are not known.
- If growing new forage crops or unique combinations of forage crops (such as peas and triticale together).
- When there are few book values available.
For a forage test to be useful, it needs to be based on a representative sample. When taking the sample, it is also important to visually assess the forage to make sure it has a good color and absence of mold.
When testing hay, the sample should be a consolidation of cores or samples taken from 15 to 20 bales. Identify similar bales from each cutting, sample a number of them, and mix the subsamples together. If hay came from several different fields or was purchased from several sources, it is best to test a sample separately from each source. Use a hay-corer to sample multiple layers of each bale. Once the samples are ready to be sent to the lab, identify them by type of forage species, cutting, or another method to help track them for future use when formulating a ration.
Same method as dry hay. Identify similar bales and mix subsamples together. Reseal the plastic after sampling to prevent mold.
Haylage or Corn Silage
For an upright, bunker silo, or bag, take samples as the forage is unloaded. Grab handfuls of forage, mix, and subsample. Sample more frequently if cuttings or quality change through the silo or bag.
Watch cows to determine what they eat and take samples reflecting their choices of grasses, clovers, and weeds. Avoid areas of contamination from manure and urine, or over-mature plants, just as the cows will. To sample, “graze” the pasture by wrapping the forage around the hand and rip it off at the post-grazing height left by the cows. Take many samples in a paddock, mix together, and take a smaller sub-sample, pack the plant material tightly in a plastic bag, and freeze to prevent the plants from changing quality due to continued photosynthesis or fermentation in the bag. After freezing for 12 to 24 hours, send the sample to the lab.
Request a wet chemistry analysis for a more accurate nutrient composition of alternative crops.
Once a representative sample has been taken, it should be analyzed by a laboratory whose accuracy has been certified by the National Forage Testing Association (NFTA). The NFTA maintains professional certification of testing laboratories around the country and annually list U.S. certified labs on their website at: www.foragetesting.org.
Forages can be analyzed by two methods, which may include chemical analysis or Near Infrared Reflectance Spectroscopy (NIR). Traditionally, laboratories used a series of chemical procedures to determine the various components important in animal nutrition (protein, fiber, minerals). NIR is a more recent technological advance which uses light to more quickly determine the nutritive value.
Interpreting a Forage Analysis
The way the information is reported will vary from laboratory to laboratory, but usually contain information on the following:
- Moisture (%);
- Dry matter (DM, %);
- Crude protein (CP, %);
- Acid detergent fiber (ADF, %);
- Neutral detergent fiber (NDF, %);
- Calcium (Ca);
- Phosphorus (P);
- Total digestible nutrients (TDN, %);
- Net energy calculations for lactation (NEL, mcal/lb), maintenance (NEM , mcal/ lb), gain (NEG , mcal/lb); and
- Relative feed value (RFV).
The information will generally be presented on an "As Fed Basis" and "Dry Matter Basis."
"As Fed" numbers describe the nutrient concentration that is in the same form received in the forage lab, so this includes all the water. Since water dilutes the nutrient concentration of the nutrients, the “As Fed” numbers will be lower than the dry matter numbers, with the exception of moisture.
Dry matter numbers allow for a more accurate comparison among different forage tests.
Fiber. ADF (acid detergent fiber) is the fiber in the forage that is the slowest to digest, and gives us information on the available energy in the forage. Lower ADF values mean higher energy and digestibility.
NDF (neutral detergent fiber) tells us what the intake potential is. If the NDF is too high, it will reduce the total amount the cow can consume. For example, a cow can only eat about 0.8% to 1% of her body weight in NDF if the forage is lower quality, but she will eat as much as 1.2% of her body weight in NDF from higher quality forage. The percentage she can eat from well managed, high quality pasture may be as high as 1.4% of body weight in NDF.
Crude protein (CP). CP is a measure of both the true protein in the forage along with the non-protein nitrogen. This is actually calculated by multiplying the amount of nitrogen in the feed and multiplying by 6.25. Since protein is one of the most expensive feed supplements to buy, a higher protein forage can help lower feed costs. However it is important to balance the amount of protein with an adequate energy supply, particularly in feeds such as a well-managed pasture with a high legume content.
Energy terms. There are several calculated energy terms on most forage tests.
NEM and NEL (net energy-maintenance and net energy-lactation) refer to the ability of the forage to meet the energy requirements of different groups of livestock, and are expressed as mega-calories (Mcal) per 100 pounds of forage. When balancing rations, dairy producers will probably use NEL, while a beef producer would be more likely to use NEM.
RFV (relative feed value) is a calculated number, which is used to compare forages with each other on an energy basis.
TDN (total digestible nutrients) is a calculation that indicates what percentage of digestible material there is in the forage
Minerals. Some forage tests will refer to the total mineral content in the forage as ash. This includes the macro-minerals, which including calcium, phosphorus, potassium, magnesium, sulfur and salt. It will also include some trace minerals such as iron, iodine, copper, cobalt, manganese, zinc and selenium.
Summary of Terms
- Dry matter: The percentage of forage that is not water.
- Moisture content: The percent water in the sample when it was tested.
- ADF: Acid detergent fiber, which is the percentage of fiber that is very slow to digest.
- NDF: Neutral detergent fiber, which is the entire fiber portion of the forage.
- CP: Crude protein which is the percentage of the forage that supplies nitrogen or amino acids (protein).
- TDN: Total digestible nutrients, which is a calculated value of overall digestibility or energy value of a forage.
- RFV: Relative feed value, which is a calculated value of overall digestibility and forage intake potential.
Forage Test Examples
Two example forage tests are provided below. Example 1 is an example of a good quality forage test. In this test of silage, NDF is 37.7, ADF is 27.7% and crude protein at 23.2%. As the plants become more mature, NDF increases, and crude protein (CP) decreases. When harvested before it is too mature, and stored correctly, a legume grass forage can be an excellent protein source A late cut, over mature hay crop may have CP levels of 8% or lower, while a well-managed pasture with high legume content will have high levels of 24% CP or higher.
Example 2 forage test is of a lower quality hay. NDF is 63.8, ADF is 40.1 and crude protein is 7.8. Another number we can use to compare these two tests is TDN which is 63 on the first higher quality sample, and is 56 on the second poor quality sample.
Example 1. Forage analysis of higher quality silage. Figure credit: Rick Kersbergen, University of Maine Cooperative Extension.
Example 2. Forage analysis of lower quality hay. Figure credit: Rick Kersbergen, University of Maine Cooperative Extension.
Also in This Series
This article is part of a series discussing organic dairy nutrition. For more information, see the following articles.
- An Introduction to Nutritional Concepts and Terminology
- Identifying Nutritional Goals
- Nutritional Requirements and Rations
- Forage Testing and Interpreting Lab Analyses
- Managing Seasonal Diet Shifts
- Assessing the Feeding Program
References and Citations
- Hedtcke, J. L., D.J. Undersander, M.D. Casler, and D.K. Combs. 2002. Quality of forage stockpiled in Wisconsin. Journal of Range Management 55: 33–42.
- Henning, J.C., G.D. Lacefield, and D. Amaral-Phillips.1991. Interpreting forage quality reports. ID-101. University of Kentucky Cooperative Extension. Available online at: https://afs.ca.uky.edu/files/interpreting_forage_quality_reports.pdf (verified 20 Nov 2019).
- Hoffman, Sullivan, K., R. J. DeClue, and D. L. Emmick. 2000. Prescribed grazing and feeding management of lactating dairy cows. NYS Grazing Lands Conservation Initiative. USDA Natural Resources Conservation Service.
- Kersbergen, R. 2010. Maximizing organic milk production and profitability with quality forages [Online]. eXtension Foundation, eOrganic Community of Practice. Available at: https://eorganic.org/node/4206 (verified 20 Nov 2019).
- Linn, J.G. and N.P. Martin. 1999. Forage quality tests and interpretations [Online]. WW-02637. University of University of Minnesota Extension. Available at: https://conservancy.umn.edu/handle/11299/207442 (verified 20 Nov 2019).
- National Research Council. 2001. Nutrient requirements of dairy cattle, 7th revised ed. National Academy Press, Washington, DC.
- Overton, T. R. and M. R. Waldron. 2004. Nutritional management of transition dairy cows: Strategies to optimize metabolic health. Journal of Dairy Science 87 (E. Suppl.): E105–E119.
- Rasby, R.J., P.J. Kononoff, and B. E. Anderson. 2008. Understanding and using a feed analysis report. G1892. University of Nebraska, Lincoln Extension. Available online at: http://extensionpublications.unl.edu/assets/html/g1892/build/g1892.htm (verified 20 Nov 2019).