Microbial dynamics during aerobic deterioration of silages

Abstract

AbstractFactors affecting microbial dynamics during aerobic deterioration of silages were evaluated in laboratory, pilot‐scale and full‐scale experiments. Yeasts usually caused the initial deterioration but in some samples with fairly good storage stability (>10 days) the activity was associated with the growth of moulds and bacteria. At a later stage, and especially at higher temperatures (>40°C), the activity was caused by bacilli. The increase in pH as a result of lactate metabolism permitted the growth of Enterobacteria. Evaluation of storage stability in samples from different levels in a bunker silo indicated low stability in surface samples and fairly good stability in samples from 160cm depth. The surface samples contained higher numbers (100–1000 times) of yeasts but the pH levels were similar.The establishment of yeasts during storage is probably due to diffusion of oxygen by leakage through the plastic cover. Compared with a plastic cover (0.1mm polythene), a rubber seal improved storage stability in laboratory silage (pH4.0) inoculated with lactic acid bacteria and infected with Candida albicans. An increase in acid content and a reduction in pH (3.7) by means of an efficient inoculant did not seem to increase the storage potential under the conditions described above. The content of adenosine triphosphate has been used as a measure of microbial activity during aerobic deterioration of silages. The main activity was concentrated at the surface (0–5cm). At 20°C, the activity was about ten times higher at the surface than at a depth of 30cm; above 30°C it was about 100 times higher.