Measuring Fiber Digestibility
Dineen, Michael; Van Amburgh, Mike
Through neutral detergent chemistry, feed is divided into a soluble fraction that is rapidly and almost completely available, and a fiber fraction that is more slowly and incompletely degraded by microbial enzymes. However, this fiber fraction might contain contaminants, such as starch, protein and ash, that can artificially inflate the concentration of NDF measured. If an artificially high NDF concentration is measured, for example in feeds with high soil contamination, the diet formulation becomes difficult, especially when balancing to low levels of diet NDF concentration. To overcome these issues, David Mertens published a method that included the option of using alpha-amylase, sodium sulfite and correcting for ash contamination and abbreviated aNDFom. Nutritionally, this is the most useful approach as it reduces the unwanted variability and contaminants in the measurement of the cell wall material. From the analysis required to quantify the intrinsic plant factors involved in aNDFom digestion we can determine the size of the fast, slow and undigested aNDFom pools and their respective rates of degradation. Within the construct of the CNCPS, this information is integrated with animal factors such as dry matter intake, passage rate, rumen pH and ammonia levels in a dynamic mechanistic approach. The latest version of CNCPS 7.0 has the capability to predict rumen pools of fast, slow and undigested aNDFom over time. These calculations are based on the constant battle between degradation and passage out of the rumen. Such an approach can help forward predict the animal response to variable feed quality, such as this years corn silage inventory.
dairy; fiber; digestibility; dry matter; intake; NDF