Aerobic Spoilage of Silages

The effect of a surface open to air on the ensiling process was investigated in 15 × 60 cm PVC silos in four trials, three with alfalfa (30, 41, and 49% dry matter, DM) and one with whole-plant corn (35% DM). Silos were sampled 1, 2, 5, 7, 14, and 28 d post-filling at 5, 20, 35, and 50 cm from the open surface. At 5 cm, little fermentation occurred as oxygen contents were at 10% or higher, and spoilage microorganisms rapidly developed causing 37 to 55% DM loss over 28 d. At 20 cm and below, oxygen levels were initially at 1% or lower. This permitted lactic acid bacterial fermentations during the first week which appeared typical of fermentations under anaerobic conditions. However, after one week, the levels of fermentation products at the 20-cm depth began to differ from those at 35 and 50 cm. In general at the 20-cm depth, lactic acid content decreased, and acetic acid content either increased or decreased relative to concentrations at lower depths. At 28 d, noticeable spoilage was beginning to occur at the 20-cm depth, as evidenced by increasing pH and elevated populations of one or more groups of spoilage microorganisms. At the end of the trials, spoilage microorganisms were also elevated at the 35and 50-cm depths relative to those normally expected in silages made under strictly anaerobic conditions.