Microbial Activities in Alfalfa and Orchard Grass Ensiled Under Certain Conditions in Experimental Silos

Abstract

I t is generally recognized that microorganisms are active in silage and that lactic acid bacteria perform a useful role in the preservation of the forage through the production of acids (1, 2, 11, 1.t). The lactic acid bacteria obviously are on the forage at the time of ensiling (1, 3), but they are present in such small numbers (8) that their usefulness in silage depends on favorable conditions for their growth and prolonged activity. Control of bacterial activity in silage by the addition of mineral acids (the A.I.V. method) to arrest bacterial development (16) has been only partially successful (6) and not recommended by some because it is economically impractical. Similarly, the use of various additives in silage as selective inhibitors of destructive bacterial action is opposed and advocated by various investigators, and their usefulness generally must depend on basic studies under various conditions. The effect of the addition of carbohydrates in various forms, such as molasses and milk by-products, on the bacterial flora of silage has been studied by various investigators (2, 7, 18). Carbohydrates were found to be effective in lowering the p i t of silage, but opinions differ as to their value in making high quality silage. Stone et al. (14) found that the addition of carbohydrates was indicated when the sugar content of the forage was low, but they believed that typical lactic acid fermentation took place irrespective of treatment and that after 2 days storage lactobacilli predominated. Salisbury et al. (11) found that the fermentation capacity was greater for simple sugars than for more complex carbohydrates, such as occur in cereal grains. Investigators who have made detailed studies of ensiled forage have observed rapid changes in the microorganisms on the forage soon after ensiling (5, 13, 15) and have attributed these changes directly or indirectly to the presence of plant juices and adequate moisture. Results of recent studies (8) indicate that the change in microorganisms on the forage begins at the time the forage is cut. Wilting of legume forages in the field to lower the moisture content has been recommended (18) and practiced widely in the making of silages, but the advantages of this method in the bacterial fermentation processes of silage making are largely unknown. In general, the literature indicates there are various methods for enhancing lactic fermentation in silage, but very little fundamental information is available on practical methods of controlling the various fermentation processes in silage