In order to reduce dry matter losses through fermentation in alfalfa silage, and thus save costs, an experiment was carried out with the application of two silage preparation in two application doses. An inoculant Lactobacillus plantarum was used in a concentration of 3×1011 cfu/g in a lower recommended dose of 1 g/t and in a higher dose of 10 g/t, as well as a preservative of 65% formic acid in a dose of 2,5 l/t and 5 l/t. Losses of dry matter by fermentation were not statistically signifi cant between the variants. Fermentation losses averaged 6,36 +- 0,85%, aerobic degradation losses averaged 2,45 +- 0,35% after two days of silo opening, and 4,54 +- 0,77% after seven days.