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

Lucerne (Medicago sativa L) silages made in test tube silos at various dry matter (DM) levels (290-537 g kg-1) with and without addition of glucose (20 g kg-1 herbage) at ensiling were stable during 7 days of aerobic exposure. Lucerne silages taken from seven farm silos were similarly stable while three others were unstable (average DM loss of 62 g kg-1 DM and pH increase from 4.35 to 7-58 in 7 days). Under similar circumstances, maize (Zea mais L) silage had a high DM loss (164 g kg-1 DM) and an increase in pH from 3.94 to 8.13. Silages were inoculated with yeast (1 x 10(6) CFU g-1 silage) isolated from aerobically deteriorating farm-scale lucerne and maize silages. The stable lucerne silages were not destabilised by inoculation, but the instability of unstable lucerne silages was increased. Aerobically unstable maize silage and stable lucerne silage were inoculated and studied separately or as a 50:50 mixture. There was a distinct lag in the development of aerobic instability in the mixture compared with maize silage alone. In another experiment, the growth of the inoculum in malt agar (pH 3.5) as affected by the presence of fresh and ensiled lucerne (six cultivars), birdsfoot trefoil (Lotus corniculatus L) and red clover (Trifolium pratense L) was studied. The legume herbages did not inhibit yeast growth whereas the corresponding silages did. Five aerobically stable lucerne silages inhibited yeast development in the media whereas unstable maize silage did not. It is concluded that aerobic stability was not related to silage DM, pH, yeast numbers or glucose addition at ensiling. Stability appeared to be due to the presence of an inhibitor (or inhibitors) produced during ensilage.