Feed Testing - Frequently Asked Questions

 
 
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 Beef Cow Rations Now that I have put up my winter feed, should I have it tested?
In most cases, feed testing enables you to make informed management decisions and to optimize animal performance during the winter months. Feed analyses can help identify nutrient deficiencies and other factors that may cause health problems, such as high nitrate levels.

What should I have the feed tested for?
That will depend the type of feeds you have, your own needs and how much you are willing to spend. In general, hay and greenfeed should be analyzed for dry matter (DM, %), crude protein (CP, %), acid detergent fibre (ADF, %), neutral detergent fibre (NDF, %), calcium (Ca, %), phosphorous (P, %), potassium (K, %) and magnesium (Mg, %). In addition, if the hay or greenfeed was baled too wet, it goes through a heating process. This process leads to the caramelization of proteins and sugars, which binds up some of the protein making it unavailable to the animal. Heat-damaged feeds are characterized by being brown to black in colour and have a sweet tobacco smell. The level of bound protein can be determined by measuring acid detergent insoluble nitrogen (ADIN, %). If the ADIN content is above 0.3% (on a dry matter basis) or makes up 15% of the total nitrogen in the forage, it went through excessive heating.

If annual forages were under any type of stress during the growing period, it is always a good idea to have a nitrate test completed. If heating occurred in your greenfeed bales you should have a nitrite test completed, as nitrites are ten times more toxic than nitrates.

Silage should be tested for the same nutrients as for hay and greenfeed, but with one very important addition, pH. Measuring the pH of the silage sample will help determine how well it ensiled. Generally, if the pH is less than 5, it is properly fermented.

If you want to test grain rations you would routinely test for DM, CP, Ca, P, K and Mg.

What about energy?
Most feed test laboratories do not directly measure the energy value of feedstuffs. They will measure the amount of ADF in the sample and then use a prediction equation to estimate the energy value. The resulting value is the level of total digestible nutrients (TDN, %) in the feed. The equation most often used for legume, grass and legume-grass hay mixtures is: TDN (%) = 88.9 – (0.779 x ADF%).

I received my feed test results, what does RFV mean?
RFV is the relative feed value. RFV is relative feed value. This measure was developed to compare quality of pure 100% alfalfa hay or silage. It is not a reliable measure for mixed hay, grass hay or cereal greenfeed. It is calculated using the ADF and NDF values of the forage, the higher the RFV the better the quality. It is used to compare forage varieties, match hay/silage inventories to animal requirements and to market hay. If the RFV is greater than 151 it is ranked as ‘prime’ quality and suitable for high producing dairy cattle. If the RFV is between 115 and 130, it will meet the needs of a beef cow and her calf. A RFV between 100 and 115 will meet the requirements of a dry cow, a heifer (18-24 months) or an idle horse.

Forage Quality and Test Interpretations
Interpreting your Forage test
Manitoba Agriculture: Moldy or Spoiled Feeds
Beef Cow Rations
Basic Beef Cow Nutrition
Know Your Feed Terms

For more information contact the Alberta Ag-Info Centre at 310-FARM (310-3276).

Prepared by Juanita Kopp, Ag-Info Centre, Alberta Agriculture and Forestry

 
 
 
 
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For more information about the content of this document, contact the Ag-Info Centre.
This information published to the web on September 15, 2003.
Last Reviewed/Revised on September 27, 2017.