The relative impacts of wilting, chopping, compaction and air infiltration on the conservation characteristics of ensiled grass

The chemical composition of baled silage frequently differs from that of comparable conventional silage. The extents of wilting, chopping, compaction and air infiltration potentially contribute to these differences in conservation characteristics. An experiment was organized in a 3 (0, 24 or 48‐h wilting to influence herbage dry‐matter content) × 2 (unchopped or chopped) × 2 (with or without compaction) × 2 (with or without air infiltration) factorial arrangement of treatments, to elucidate the relative effects of these factors on the conservation characteristics of ensiled grass. Dry‐matter content of herbage and infiltration of air had a greater effect on silage conservation characteristics than chopping and compaction. The main interactions were between wilting and air infiltration, wilting and compaction, and compaction and air infiltration. Air infiltration stimulated a secondary fermentation in the unwilted herbage, reflected in a large increase (P < 0·001) in clostridial activity. As wilting progressed, air infiltration facilitated yeast respiration of water‐soluble carbohydrates (WSC) and resulted in an increase (P < 0·001) in in‐silo fresh‐weight losses. Compaction reduced (P < 0·05) silage pore space and, as a result, the extent to which air could penetrate the silage mass. Compaction of the wilted herbage restricted respiration and was reflected in increased (P < 0·05) concentrations of WSC and in a reduction (P < 0·001) in fresh‐weight loss. The rapid achievement and maintenance of adequately anaerobic conditions is the primary requirement for baled silage. This study showed that failure to achieve this will lead to progressively greater losses, especially with drier herbage.