Factors influencing aerobic deterioration of silages and changes in chemical composition after opening silos

Abstract

AbstractIn five separate experiments, silages made from Italian ryegrass by eight treatments were transferred into expanded polystyrene containers and the occurrence of deterioration was observed at 25–30 °C and 10–15 °C or 5–10 °C by measuring changes in temperature during 7 days. The treatments were: heavily wilted, slightly wilted, unwilted, and 2% glucose added to unwilted grass—all carried out with and without addition of 0.5% sodium propionate (in one experiment a mixture of 0.08% sodium nitrite and 0.04% hexamethylenetetramine was used instead). Silages tended to be less stable at 25–30 °C than at 10–15 °C ambient temperature, although some were stable even at the higher temperature. At 5–10 °C, no deterioration occurred. No definite relationship was found between occurrence of deterioration and the contents of dry matter or WSC in silage or density in the container. Although deterioration took place more often at pH lower than 4.0, no relationship between pH and deterioration was recognised in the range 4.0–7.0. Silages tended to be more stable when contents of total or lactic acid in fresh matter were high. Silages with no added propionic acid were more susceptible to deterioration but some were unstable even at high propionic acid levels. No aerobic deterioration took place with silages containing more than 0.5% butyric acid. With the deteriorated silages, rises in pH value (except for those with originally high pH), marked decreases in lactic acid and/or WSC were observed. Propionic acid content tended to remain constant in the stable silages but there were a few exceptions. Losses of WSC plus organic acids during deterioration were found to be higher with the silages of high WSC contents. Although changes with the stable silages were generally small, a few of them showed some decrease in WSC and/or organic acids.