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Types and Sequence Change of Bacteria in Orchardgrass and Alfalfa Silages

Dairy Cattle Research Branch, USDA, Beltsville, Maryland

ABSTRACT

The types and sequence change of lactic acid bacteria in 30 orchardgrass and alfalfa silages have been determined. The 3,142 strains studied were representative of silage quality, different cuttings, and stages of fermentation. Both cocci and lactobacilli were found on the forages and in the silages. It was generally true that better quality silages were obtained when the early bacterial flora consisted predominantly of cocci. Most cocci, except the pediococci, disappeared a few days after ensiling. In the good quality silages, three species of lactic acid bacteria emerged as the dominant population. These included Lactobacillus brevis, Lactobacillus plantarum, and pediococci. L. brevis was usually found in the later stages of fermentation and was more prevalent in the alfalfa silages. In the poor quality silages, four species were found, including the three mentioned above and Lactobacillus casei (variable), an attenuated strain of lactobacilli. The results do not directly explain why the low acid producing strains reached such high numbers in poor quality silages. It is suggested, however, that a series of interacting factors may be responsible for selecting certain organisms. Among these are included entrance of air into the forage mass, increased temperature, and amino acid imbalance. These factors assume an important role in determining the course of the fermentation, especially in the conflict between the lactic acid bacteria and the spore-forming anaerobes.