AbstractGrass (220 g DM kg−1was ensiled after adding 106and 108enterobacteria (90%Rahnella aquatilis, 9·9%Hafnia alveiand 0·1%Escherichia colig−1fresh mutter. The silages were exposed to aerobic conditions alter 125 d of storage. In all treatmentsH. alveirapidly superseded the initial high number ofEnterobacter agglomerans(naturally present) andR. aquatilis.The maximum number of enterobacteria was detected about I d after initiation of fermentation. After 4 d of fermentation, when concentrations of undissociated lactic and acetic acids ranged from 52 to 36 mM and 41 to 51 mM respectively, no enterobacteria were detectable. Inoculating the crop with enterobacteria restilted 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 μg g−1fresh 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 andBacillusspores, 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