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United States Department of Agriculture

Agricultural Research Service


item Undersander, Dan
item Martin, Neal
item Mertens, David

Submitted to: American Forage and Grassland Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/15/2005
Publication Date: 6/6/2005
Citation: Undersander, D., Martin, N., Mertens, D. 2005. What are the differences between forage testing laboratories and the impact on you operation? In: Proc. 2005 Annual Conference Volume 14 [CD-ROM]. American Forage and Grassland Council. 5 pp.

Interpretive Summary:

Technical Abstract: Many farmers are concerned about the accuracy of the forage tests they receive. However, we should focus on the true objective of forage testing, which is to predict animal performance when the forage is fed in a balanced ration. To this end, the farmer must consider all aspects of forage sample handling and analysis. The questions the farmer needs to consider are 1) how representative is the sample of the hay, haylage or silage that is submitted for analysis; 2) how accurately is the laboratory performing forage analyses; and 3) how well does the analysis predict animal performance? Farmers can improve accuracy of prediction by sampling well and submitting multiple samples; by selecting laboratories that participate in the National Forage Testing Association proficiency certification program and use reference methods; and by choosing analyses that accurately predict animal performance. Numerous studies have shown that the variation among samples taken from the same lot of forage varies from ±2.5 to ±0.6 %-units as number of core samples increases from 3 to 20. Thus, it is recommended that 20 core samples be taken to adequately represent a lot of forage. The National Forage Testing Association manages a proficiency testing program by submitting six forage samples to participating laboratories annually and reporting how closely their results compare to results from established reference methods. Laboratory performance is based on the analyses for dry matter, crude protein, acid detergent fiber and neutral detergent fiber. When they use reference methods 66% of the results from laboratories are within 0.2, 0.5 and 0.6% for crude protein, acid detergent fiber and neutral detergent fiber, respectively. These deviations are similar to those for a good representative sample. Traditionally, fiber concentration has been related to animal performance, but this relationship is not exact. Currently, in vitro fiber digestibility is being used to improve our accuracy of predicting total digestible nutrients in feeds. Although in vitro methods are more variable, they should be included as a tool to improve feed evaluation. In conclusion, accurate prediction of nutritive value requires a representative sample, accurate laboratory analyses, and improved feed evaluation methods. Although differences in results among laboratories exits, they are comparable to those associated with sampling and with relationships between laboratory methods and animal performance. Farmers can increase the value of forage analysis by submitting multiple samples, selecting laboratories that participate in proficiency certification programs, and adopting new feed evaluation methods that more accurately reflect animal performance.

Last Modified: 05/21/2017
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