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) enter obacteria (90% Rahnella aquatilis, 9.9% Hafnia alvei and 0.1% Escheric hia coli) g(-1) fresh matter. The silages were exposed to aerobic cond itions after 125 d of storage. In all treatments H. alvei rapidly supe rseded the initial high number of Enterobacter agglomerans (naturally present) and R. aquatilis. The maximum number of enter obacteria was d etected about 1 d after initiation of fermentation. After 4 d of ferme ntation, when concentrations of undissociated lactic and acetic acids ranged from 52 to 86 mM and 41 to 51 mM respectively, no enterobacteri a were detectable. Inoculating the crop with enterobacteria resulted i n a temporarily retarded rate of production of lactic and acetic acids and a 50% increase in the concentration of ammonia-N. The concentrati on 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 ae robic stability of the silages. There was a lag in the decrease in con centrations of acids and delays in the increase in pH, respiration rat e and numbers of yeast and Bacillus spores. In uninoculated silages th e pH increased from 4.1 to 5.0 after 8 d of aerobic storage, whereas i n inoculated silages a pH of 5.0 was not reached until after 16 d of s torage.