Effects of partial dehydration methods on high-moisture forages chemical composition

This study evaluated whether partial dehydration methods alter the chemical composition of high-moisture forages. Two experiments were conducted. In Experiment 1, 20 maize silage samples were subjected to freeze-drying, forced-air oven drying, forced-air oven drying preceded by a microwave preheating step, or microwave drying. In Experiment 2, 28 forages (silages, fresh grasses, and fresh legumes) were evaluated using freeze-drying, forced-air oven drying, microwave drying, or air-fryer drying. Method effects were assessed based on water removal efficiency, nitrogenous and fibrous compound profiles, in vitro digestibility, indigestible fibre, and colorimetric properties. Microwave and air-fryer drying removed less water than freeze-drying and resulted in greater differences in nitrogenous compound concentrations and profiles, including apparent N volatilisation and greater concentrations of detergent-insoluble nitrogen. Heat application inconsistently affected fibrous components but consistently reduced in vitro dry matter digestibility without altering in vitro fibre digestibility, likely reflecting starch retrogradation and production of heat-derived artefacts soluble in neutral detergent. These modifications were most pronounced in fresh forages, indicating an interaction with their chemical matrix. Among heat-based methods, forced-air oven drying produced the least chemical alteration. Overall, heat application during partial dehydration modifies the chemical characteristics of high-moisture forages, and when freeze-drying is not feasible, forced-air oven drying best preserves the original sample composition.