INFLUENCES OF ENTEROBACTERIA ON THE FERMENTATION AND AEROBIC STABILITY OF GRASS SILAGES

Grass (220 g DM kg(-1)) was ensiled after adding 10(6) and 10(8) enterobacteria (90% Rahnella aquatilis, 9.9% Hafnia alvei and 0.1% Escherichia coli) g(-1) fresh matter. The silages were exposed to aerobic conditions after 125 d of storage. In all treatments H. alvei rapidly superseded the initial high number of Enterobacter agglomerans (naturally present) and R. aquatilis. The maximum number of enter obacteria was detected about 1 d after initiation of fermentation. After 4 d of fermentation, when concentrations of undissociated lactic and acetic acids ranged from 52 to 86 mM and 41 to 51 mM respectively, no enterobacteria were detectable. Inoculating the crop with enterobacteria resulted in a temporarily retarded rate of production of lactic and acetic acids and a 50% increase in the concentration of ammonia-N. The concentration of endotoxin in the silages was 6-7 mu g g(-1) fresh matter. There was no change in the level of endotoxin during ensiling. High numbers of enterobacteria at the beginning of the fermentation improved the aerobic stability of the silages. There was a lag in the decrease in concentrations of acids and delays in the increase in pH, respiration rate and numbers of yeast and Bacillus spores. In uninoculated silages the pH increased from 4.1 to 5.0 after 8 d of aerobic storage, whereas in inoculated silages a pH of 5.0 was not reached until after 16 d of storage.