Forage Testing

Clay Talton - Elbert County ANR Agent

            In the county extension office we are continuously asked questions about testing forage for nutrients.  Most producers are asking me “how much does it cost” and “what’s the benefit.” A forage test is a vital part to any livestock operation.  Forage for livestock plays a vital role in daily nutrition and without an understanding of the nutrients being provided it is impossible to know if an operation is feeding their animals to meet their daily nutritional needs.  Daily intake of animals changes with age and nutritional needs change with age and stage of production.  With that being said, a forage test is critical to ensuring a lot of hay is fed correctly with or without supplementation based on the report.

So how do I take a forage sample? Well the first step is easy…call your County Extension Agent! Your County Agent can provide you with information on proper testing methods for the forage you want to test and let you know what it cost.  Also, they can help you determine what test you need depending on nutrients you are concerned with.  In order to have an accurate forage test it is imperative to get a representative sample.  The method of sampling can vary with types of forage.  Most commonly, we are sampling baled hay from round or square bales.  When sampling hay, use a core sampler.  The most common types of core samplers are the Penn State Forage probe that attaches to the end of a drill or hand brace and the Colorado Hay Probe.  Take 10 to 20 core samples from each hay lot then composite and mix for analysis. Small rectangular bales should be sampled by coring from the end. Large hay bales should be sampled from the front or back (not the sides) in order to get a cross section of the rolled hay. If sampling baleage, be sure to tape over the hole from where core was taken.  Drop your sample by your local extension office and be sure to give them all of the information regarding the specie of livestock you are feeding.

So what’s next? Well, you should receive your report from your local extension office detailing the results of the hay you tested.  If you have questions, don’t hesitate to ask your County Agent about how to feed the hay and to get help in determining if the hay will meet the current nutritional needs of your animals.  Also, they can help you to determine what, if any, supplementation is needed. 

Interpreting a forage report can be somewhat overwhelming for a first time forage tester.  Most producers are concerned with relative forage quality (RFQ), crude protein (CP), total digestible nutrients (TDN), Dry Matter (DM) and nitrates. RFQ is an index for ranking forages based on a comprehensive analysis. It is calculated from CP, Acid Detergent Fiber (ADF), Neutral Detergent Fiber (NDF), fat, ash and NDF digestibility. RFQ is based on a scoring system where the higher the RFQ, the better the quality. This value is a single, easy to interpret number that improves producer understanding of forage’s quality and helps in establishing a fair market value for the product. See the following extension publication, Using Relative Forage Quality to Categorize Hay, to learn more about RFQ.  Crude protein is the total protein in the sample including true protein and non-protein nitrogen. Protein is required on a daily basis for maintenance, lactation, growth and reproduction. Total digestible nutrients is the sum of the digestible fiber, protein, lipid, and carbohydrate components of a feedstuff or diet. TDN is directly related to digestible energy and is often calculated based on ADF. Nitrates can become a problem when fed in high amounts. Nitrate accumulator plants include sorghum, sorghum sudangrass, sudangrass, weeds and small grain forages. Table 1 shows the values that are represented on a forage test and when to use caution if those values reach a high value.

Table 1.

Forage Nitrate

(ppm dry forage)                               Guidance                 

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Safe to feed with adequate feed and water

4,500 - 6,500                                       Safe under most conditions but, if feeding pregnant animals, restrict to one-half (1/2) of the ration

6,500 - 9,000                                       Limit to one-half (1/2) of the ration

9,000 - 15,000                                     Limit to one-third (1/3) of the ration

15,000 - 18,000                                   Limit to one-quarter (1/4) of the ration

>18,000                                               Potentially lethal, very risky, dilute carefully

Drought, frost, fertilization and manure application practices are factors that can lead to high nitrate levels. When nitrate is converted to nitrite, it impedes the uptake of oxygen by the blood resulting in death due to lack of oxygen. Blood becomes brownish in color and exterior membranes may become bluish in color. Dry matter is the moisture-free content of the sample. Because moisture dilutes the concentration of nutrients it is important to always balance and evaluate rations on a dry-matter basis.

Once you have determined how to feed your hay, don’t forget that the nutrient needs of livestock are constantly changing based on age and stage of production.  Be sure to test every lot of hay you bale or buy and to adjust any additional supplementation being used as an animal’s stage of production changes.  If you have high quality hay that is providing an excess of nutrients for the stage of growth or production of your animal, be sure to save it and use lower quality hay that will meet their needs.  The little amount of money required to test a lot of hay can save you hundreds in the long run.