Artifacts and interpretations of in situ ruminal neutral detergent fiber degradation kinetics of forages

Three experiments were conducted to evaluate the effects of sample grinding techniques, filter bag preparation, and postincubation washing methods on NDF disappearance and degradation kinetics. In experiments 1 and 2, samples of corn silage, alfalfa hay, grass hay, and triticale silage were dried and ground to pass a 6-mm screen, then further processed through either a 1-mm cutter mill (CUT) or a 1-mm cyclone mill (CYC). Filter bags were filled with forage samples and either prerinsed with acetone (ACE) or left untreated (CON). Experiment 1 assessed NDF disappearance from bags subjected to various washing procedures without ruminal incubation. Experiment 2 evaluated in situ NDF disappearance after 0, 3, 6, 12, and 24 h of ruminal incubation followed by different washing methods. Experiment 3 extended incubation times to 240 h and compared hand wash (HW) versus machine wash (MW) treatments. All experiments followed a randomized complete block design with forage type as a random effect and grinding method, bag preparation, and washing procedure as fixed effects. Results from experiment 1 showed ACE bags retained more NDF than CON bags, and CYC grinding increased NDF disappearance, especially with MW. In experiment 2, significant interactions among grinding, bag preparation, and washing were observed, though NDF disappearance was minimal at short incubation times (<12 h). Experiment 3 revealed higher undigested NDF concentrations with HW and CYC grinding, with no interaction between grinding and washing methods. Cyclone grinding produced finer particles, contributing to greater NDF disappearance even in the absence of microbial activity. These findings underscore the need for methodological standardization to ensure accurate and biologically meaningful forage evaluation.