Author
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Mertens, David |
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Submitted to: Proceedings of the Western Nutrition Conference
Publication Type: Proceedings Publication Acceptance Date: 8/1/2006 Publication Date: 9/19/2006 Citation: Mertens, D.R. 2006. Do We Need to Consider NDF Digestibility in the Formulation of Ruminant Diets?. In: Proceedings of the 27th Western Nutrition Conference, September 19-20, 2006, Winnipeg, Manitoba, Canada. p. 75-98. Interpretive Summary: Technical Abstract: Both NDF and NDFD can affect ration formulation and animal performance. Their value depends on the accuracy and precision of measuring each. The determination of NDF is done most accurately using the amylase-treated NDF method, which uses both sodium sulfite and amylase and has a standard deviation of reproducibility among laboratories for a single analysis of ±1.3 %-units of aNDF. In vitro methods for measuring NDFD are much more variable than those for NDF and there is no accepted standard method. At best and within a laboratory, the standard deviation of repeatability for single determinations of NDFD is 1.5 to 2 times that of NDF determination. The standard deviation of reproducibility among laboratories for single in vitro determination is 3 to 5 times that of NDF. The high variability in measuring NDFD increases the risk of using it to formulate or adjust diets. Often the variability in measuring NDFD is reduced by increasing replication, which should be done across rather than within days; however this increases the cost and time required for analysis. Systems are available for using NDF and NDFD to estimate the energy value or DMD of feeds. Various summative equations can be used to estimate DMD or TDN from NDF and NDFD. Systems are also available for formulating rations for maximum and minimum forage using NDF or physically effective NDF. A summary of comparisons between high and low digestibility forages indicates that NDFD is related to NDF intake. This relationship was used to develop a system that accounts for the impact of both NDF and NDFD on ration intake and digestibility to maximize forage composition of rations that also maximize animal performance and health. In conclusion, we probably should consider differences in the NDFD of forages when formulating ruminant diets. However, the impact and value of NDFD must be kept in perspective and should be used appropriately for the situation. The measurement of NDFD is several times more variable than NDF, making quantitative use of the information difficult. Although NDFD can have an impact on ration formulation and animal performance, NDF concentration in feeds and the diet has much greater impact. The impact of changing NDFD among sources is much less than the impact of differences in NDF and NDS among sources of feeds. Thus, it is most important to insure that the NDF and energy density of the ration are suitable for the animal. Variation in NDFD in forages is of secondary importance and should be used to fine-tune rations. If rations are formulated to have high energy density (low fiber content) in relation to animal requirements and forages contribute a small portion of the NDF in the ration, then the primary impact of NDFD is on the energy value of the forage. Various summative equations can be used to adjust the energy value of the forage for changes in NDFD. If rations are formulated to maximize the proportion of forage in the ration, then the impact of NDFD on intake as well as energy value should be considered. |