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Chemical and Bacteriological Changes in Grass Silage During the Early Stages of Fermentation. II. Bacteriological Changes

Dairy Cattle Research Branch, Animal Husbandry Research Division, Agricultural Research Service, Beltsville, Maryland

ABSTRACT

The results showed that aeration of the forages influenced the bacterial flora and the chemical quality of the silages examined.

The majority of the organisms isolated from the silages during the early stages of fermentation were cocci and Gram-negative rods. A few diphtheroids, aerobic bacilli, and pseudomonads were found, but occurred too infrequently to be of importance. Lactobacilli were usually present in high percentages during the late stages of fermentation.

Only minor differences were observed in the growth rates and total numbers of viable bacterial cells in good and poor silages, and the percentages of acid-producing bacteria in different crops and cuttings were similar.

The streptococci and Gram-negative bacteria were prominent during the initial stages of ensiling. In the poor silages the Gram-negative bacteria reached higher percentages and decreased slower than in the good silages. Streptococci and leuconostocs were observed in the late stages of fermentation. The good silages demonstrated a typical sequence in that the cocci, with the exception of the pediococci, and Gram-negative rods disappeared and the high acid-producing lactobacilli predominated.

The results emphasized the importance of the cocci during the early stages of ensiling. Favorable pH values were obtained in silages when the cocci were in control of the fermentation.

The presence of high numbers of lactobacilli on fresh plants did not necessarily determine the quality of the silage. In the better-quality silages the fermentation was initiated by the streptococci, later supported by the pediococci and leuconostocs, and completed by the lactobacilli.

Since the proportions of acid-producing bacteria were not much different in the silages, it is suggested that the deterioration of the aerated silages was a result of substrate depletion which affected the metabolism of the bacteria. When they were unable to produce enough preserving acids the sporeforming anaerobes were able to compete.