AEROBIC DETERIORATION OF LUCERNE (MEDICAGO-SATIVA) AND MAIZE (ZEA-MAIS) SILAGES EFFECTS OF FERMENTATION PRODUCTS

Eleven laboratory lucerne silages, ten farm-scale lucerne silages and one maize silage were analysed for fermentation products to determine if chemical composition could explain differences in aerobic stability. Three of the farm-scale lucerne silages and the maize silage heated within 4 days of exposure to air whereas the other lucerne silages were stable for longer than 7 days even after inoculation with a destabilising yeast inoculum. The silages were analysed for lactic acid, volatile fatty acids (C1 to C6), succinic acid, ethanol, and 2,3-butanediol. The concentrations of these compounds in the unstable silages were not different from levels found in stable silages on either a dry matter basis or an undissociated water basis. However, unstable silages tended to be lower in 2,3-butanediol than other silages. The time until heating in these silages was simulated using a model of aerobic fungal growth in silage. This model considered the effects of yeast and mould numbers, pH, moisture content, and lactic and acetic acid concentrations on stability. Aerobic stability in three of the four unstable silages, with and without inoculation of destabilising yeasts, was reasonably predicted by the model. Stability in the other silages was consistently underpredicted by the model. These results indicate that the stability factor found in many lucerne silages is unlikely to be one of the principal products of silage fermentation.