The Enid News and Eagle, Enid, OK

January 4, 2014

Forage testing is an important tool

By Rick Nelson, Extended Forecast
Enid News and Eagle

ENID, Okla. — Forage testing is a tool to determine current nutritive values as well as non-nutritive values in forages that can be used for marketing hay, formulating rations and determining potential toxicities or other problems such as prussic acid or nitrate.

How to sample for testing

For rectangular square bales, forage sampling should be done by coring in from the ends. For large round bales, forage samples should be taken from the sides not the front or back, to get a cross section of the rolled hay. When sampling hay from bales, it is important to use a core sampler rather than using hands to get a representative forage sample. Check with your local county extension office for the availability of a core sampler and sample bags.

Take a separate sample from each field and cutting; otherwise, forage quality analysis can give you misleading information. Take at least 20 core samples from each hay lot, composite the samples, mix them thoroughly and take a sub-sample for analysis. Put the sub-sample into a clean, airtight plastic bag with a label including your name, address, forage type, stage of maturity and date harvested.

Terms and interpretation

• Moisture is the water present in the forage and is expressed as percent.

• Dry matter (DM) is the percentage of the forage that is not water. 100 minus moisture content gives dry matter percentage (i.e., if moisture is 65 percent, then dry matter percentage is 35 percent, 100-65 percent = 35 percent)

• Crude protein is the amount of nitrogen in the forage. It is the sum of true protein and non-protein nitrogen. True protein, such as microbial protein, is utilized in rumen as the food for rumen microbes. Non-protein nitrogen, such as urea, is utilized in the small intestine. Since protein has about 16 percent nitrogen, crude protein can be obtained by multiplying percent nitrogen by 6.25 (i.e., if nitrogen concentration is 3 percent, the crude protein would be 3 percent N x 6.25 = 18.75 percent)

• Acid detergent fiber (ADF) is the sum of hemicellulose, cellulose and lignin. ADF is used as a predictor of digestibility and energy value, and is inversely related to digestibility (i.e., as the ADF percentage increases, then digestibility and energy value decrease).

• Neutral detergent fiber (NDF) is the sum of hemicellulose and lignin. NDF is a predictor of feed intake potential or gut fill in rumen, and is inversely related to feed intake (i.e., if the NDF is low, then feed intake can be high). In general, forage legumes tend to have lower NDF values than grasses although it depends on the stage of maturity at harvesting.

• Total digestible nutrients (TDN). TDN is directly related to digestible energy and is the sum of digestible fiber, starch, sugars, protein and fat in the forage. TDN is useful for beef cow rations that are primarily forage.

• Net energy maintenance (NEM) and lactation (NEL). Net energy is the energy concentration in a feed. It can be measured by laborious animal trials or can be predicted using either ADF or NDF. Older forages have higher fiber and less energy than younger, succulent forages. Thus older forages have lower net energy values than younger forage plants. Most dairy producers generally use NEL to balance rations for lactating cows while some beef producers use NEM.

• Relative forage value (RFV). RFV is an index used to rank forages based on ADF and NDF values. No unit value is used for RFV. It measures overall feed value of forage and it is used in hay markets, in particular alfalfa.

Nelson is Oklahoma Cooperative Extension Service ag educator for Garfield County.