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

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Figure 7: Relationship between 96hr NDFD and ether linked FA in NDF residues NDFd Procedure The in-vitro procedure used to obtain a NDFd value is used to calculate a rate of NDF digestion. We therefore want to control of all the factors that would bias the calculation. Besides the estimation of the iNDF, other important factors are the lag and the pool size. It is therefore a must minimizing the lag and avoiding loss of sample during the procedure: - Fast handling of rumen fluid from the barn to the lab - Care in keeping the rumen fluid temperature at 39° C and anaerobic - Filtration of the fluid and not blending - Total time between barn and inoculation of the samples should not be higher than 20-25 minutes. - Use of glass microfiber filter 934-AH or GF/C with porosity of 1.5 µ (Whatman) - Particular care of hot weighing because of filters and moisture variation - Use of blanks for inoculums/filter loss/gain correction ADL Procedure Variation in the ADL procedure has been observed in many laboratories and is especially observed n lower lignin forages, like bmr corn silages, higher digestibility corn silages and immature grasses. Better care should be devoted to this types of forages during the procedure. Use of glass microfiber filter like 934-AH or GF/C is highly recommended along with more attention during the hot weighing. The removal of asbestos as a filtering agent has most likely contributed to increased variation in ADL recoveries. Also, use of blanks is recommended because of possible sulfuric acid degradation of filters. To decrease the chance of filter degradation, the sample can be put in a small beaker (50 to 100 ml) soaked in excess sulfuric acid, stirred appropriately and then filtered in crucibles with filters.
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. REFERENCES Bibby, J. and H. Toutenburg. 1977. Prediction and improved estimation in Linear Models. Ch.1. John Wiley and Sons, New York. Besle J. M., A. Cornu and J.P. Jouany. 1994. Role of structural phenylpropanoids in forage cell wall digestion. J. Sci. Food Agric 64 171-190. Casler, M.D. 2001. Breeding forage crops for increased nutritional value. Advances in Agronomy 71:51-107. Chandler, J.A., W.J. Jewell, J. M. Gossett, P. J. Van Soest, and J. B. Robertson. 1980. Predicting methane fermentation biodegradability. In: J. Biotech. and Bioengineering Symp. 10, John Wiley and Sons. Pp. 93-107. Conrad, H. R., W. P. Weiss, W. O. Odwongo, and W. L. Shockey. 1984. Estimating net energy lactation from components of cell solubles and cell walls. J. Dairy Sci. 67:427-436 Danfær A., P. Huhtanen, P. Uden, J. Sveinbjornsson and H. Volden, The nordic cow model, Karoline—description. In: E. Kebreab, J. Dijkstra, A. Bannink, W.J.J. Gerrits and J. France, Editors, Nutrient digestion and Utilization in Farm Animals—Modelling Approaches, CABI Publishing, Wallingford (2005), pp. 383–407. Ellis, W. C., Matis, J. H., Hill, T. M. and M. R. Murphy. 1994. Methodology for estimating digestion and passage kinetics of forages. In: Forage quality, evaluation and utilization, Ed G C Fahey Jnr., American Society of Agronomy: Crop Science Society of America: Soil Science Society of America. Madison, Wisconsin, USA. Ellis, W. C., D.P. Poppi, J.H. Matis, H. Lippke, T.M. Hill and F.M. Rouquette. 1999. Dietarydigestive-metabolic interactions determining the nutritive potential of ruminant diets. In: H.J.G. Jung and G.C. Fahey Jr., Editors, Nutritional Ecology of Herbivores, American Society of Animal Science, pp. 423-481. Ellis, W. C., M. Mahlooji and J.H. Matis. 2005. Models for estimating parameters of neutral detergent fiber digestion by ruminal microorganisms. J. Anim. Sci. 83:1591-1601. Ellis, W. C., D. P. Poppi, J. H. Matis, H. Lippke, T. M. Hill, and F. M. Rouquette, Jr. 1999. Dietary-Digestive-Metabolic Interactions Determining the Nutritive Potential of Ruminant
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aNDF, NDFd, iNDF, ADL and kd: What have we learned?

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