The aim of this experiment was to assess the effect of the new type of silage additives on the result of the fermentation and aerobic stability of the silage alfalfa (Medicago sativa), harvested with about 32% of dry matter content and with different cutting length. Compared to control silages without additives, but also with silages preserved with different, in practice, already used silage products, the two new products tested did not show a significant difference in nutritional value or fermentation quality. The new silage additive (CZ 032516 U1) showed higher aerobic stability, particularly for silage chopped shorter.