Why new fiber analyses: A perspective
aNDFom
1960s: NDF is introduced to describe the total fiber content of feed, collectively the hemicellulose, cellulose and lignin. The dried and ground sample is boiled in NDF solution for an hour to remove the unwanted nutrients leaving the fiber residue behind. Various reagents are included in the solution to wash out the protein, fat, starch, etc. and leave the fibrous residue behind.
1990s: Amylase and sodium sulfite are added to the ND solution to further clean up the residue. Amylase was added to help breakdown the starch in high starch feeds. Likewise, sodium sulfite was added to help remove protein.
Today: It is being advocated that NDF be reported on an "organic matter" or "ash free" basis. Samples high in ash can overwhelm the ND solution and not all of the ash is washed out. The remaining ash is included in the fiber residue, resulting in an overvaluation of the NDF. In these situations, NDF is overestimated and the diets formulated around this value can lead to underfeeding fiber and the problems associated with it (such as off feed, acidosis, or foot problems).
Following the traditional NDF extraction, the fiber residue is ashed at 600C for 2 hours to burn off the organic matter, leaving the ash behind. The residual ash is subtracted from the fiber residue to determine and express the NDF on an ash free or organic matter basis. This will be reported as aNDFom. The data in Table 1 represents a comparison of the conventional aNDF with aNDFom across 100 samples for each feed type. Note that the "hi diff" column represents the greatest difference observed along with the ash content of that sample in the last column.
Most current ration software is based on aNDF and this value will continue to be reported in our regular packages. aNDFom will be replacing aNDF in our CNCPS 6.5 model driven packages (327) NIR Pro and wet chemistry (315) Model Profile.
uNDFom
To be consistent with the utilization of aNDFom, a new series of NDF digestibilites are available on an organic matter basis. For example, the undigested NDF and NDF digestibility determined at 30 hours will be reported as uNDFom30 and NDFDom30, respectively. The NDFDom30 will be used in conjunction with two new digestibilities measured at 120 and 240 hours. Cornell has determined that using these 3 time points will result in a better estimation of the rate of digestion known as kd. In a rate calculation, it is important to know the end point, which in this case is the total undigestible fiber. In previous editions of the CNCPS, this was estimated as a constant (lignin x 2.4). Recent research has demonstrated that this value is best determined as the undigested fiber remaining after a 240 hour incubation in rumen fluid.
Figures 1. & 2. illustrate fiber breakdown for corn silage and haylage over time. Graphed below is the average for the feed type plus the highest and lowest digestibility for the feed type in the data set.
Likewise, the kd for non-forages can now be calculated using NDFDom values measured at 12, 72 and 120 hours. To support the need for these values, we're offering the following wet chemistry packages:
(585) Forage NDFDom $77
Includes: aNDFom, uNDFom and NDFDom at 30, 120 & 240 hrs.
(586) Non-forage NDFDom $77
Includes: aNDFom, uNDFom and NDFDom at 12, 72, & 120 hrs.
Please realize that these are time-intensive procedures and require 2 - 3 weeks to complete.
Additional reading:
Raffrenato, E. and M.E. Van Amburgh. 2010. Development of a mathematical model to predict sizes and rates of digestion of a fast and slow degrading pool and the indigestible fiber fraction. Proc. Cornell Nutr. Conf. p. 52-65.
Cotanch, K.W., R.J. Grant, M.E. Van Amburgh, A. Zontoni, M. Fustini, A. Palmonari and A. Formigoni. 2014. Applications of uNDF in ration modeling and formulation. Proc. Cornell Nutr. Conf. p. 114-129.
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