aNDF, NDFd, iNDF, ADL and kd: What have we learned?

Take Home Messages
� Description of NDF digestion and kinetics have been often biased and limited by
laboratory and mathematical errors. A more accurate and precise intrinsic kd
estimation is today possible with the tools now available.
� The ―anchor points‖ (lag and iNDF) are confirmed to be the most important
factors to prevent bias. Lag can be easily minimized within laboratory. Estimation
of true iNDF can be accomplished either by long in-situ or in-vitro digestion using
small pore size bags o filters, respectively.
� In the near future calculation of iNDF using forage group-specific equations will
be possible, and will need to be validated for environment and climate
differences. Rates of digestion and pool sizes will then change accordingly.
� Use of smaller pore size filters is highly recommended for NDF and ADL
procedures to avoid loss of fine particles and biased calculations of NDFd, kd’s
and iNDF.
� With the exception of legumes, phenolic acids, type of lignin and their different
chemical linkages to cell wall carbohydrates explain almost all of the variation in
NDF rate and extent of digestion both in-vitro and in-vivo. These factors vary
however by forage group and maturity.
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Dietary-Digestive-Metabolic Interactions Determining the Nutritive Potential of Ruminant