Knowledge Bank

Fiber is the carbohydrate portion of feed that can only be digested by gastrointestinal microbes. The neutral detergent fiber (NDF) system is used to calculate three fiber components of a sample: lignin, cellulose, and hemicellulose. Accurate NDF measurements are beneficial when calculating nutritional value and digestibility of feeds. Dual-flow continuous culture fermenters (DFCC) are used to mimic rumen function and examine feedstuff digestibility without the cost of an animal trial. Effluent samples from fermenters are finely ground, which makes it more challenging to filter the sample during the NDF procedure. Our hypothesis was that the 934-AH microfiber filters (MF) would be more accurate for determining NDF content of fermenter samples. Our second hypothesis was that ash percentage in feed samples would have a direct effect on NDF accuracy. Therefore, our objectives were to compare filter types (paper vs. microfiber) and determine which was more accurate compared to a commercial laboratory standard. Our secondary objective was to evaluate the effect of ash contamination on NDF results. To make this comparison, dried effluent samples (n=24) from 3 previously published DFCC trials were assayed for NDF in triplicate and filtered by 541 paper filters (PF) or MF. In a second experiment, 3 feed samples (alfalfa hay, brewer's grains, and corn silage) were dried (55C), ground (2mm), and assayed for NDF using the PF. Ash was obtained by ashing biochar at 500C. Each feed sample was contaminated with a differing level of ash (0%, 20%, 30%, 40%, and 50%) and run in triplicate. In a third experiment, the 3 feed samples were contaminated with either 0%, 25%, and 50% ash obtained from ashing alfalfa pellets. These samples were assayed for NDF in triplicate and were corrected for ash contamination. The MF and PF had a mean difference from the commercial laboratory standard of -2.86 and -2.50 respectively (P < 0.0001). In experiment 2, ash contamination had a direct effect on increasing the amount of NDF retained on the filter (P < 0.0001). In experiment 3, the NDF values were not affected by ash contamination when corrected for ash content. These data indicate that ash contamination has a significant effect on the recovery of NDF values using the reflux method. Since DFCC effluent samples contain around 50% ash, more work is needed to determine the best method to obtain accurate NDF values.