The objective of this research was to evaluate the effect of a microbial inoculant (Land O’Lakes) on the fermentation of alfalfa silage ensiled at 2 levels of DM. Alfalfa from the same field was wilted to 38 (mid-DM, mDM) and 46% (high DM, hDM) DM. Forages were untreated (CN) or treated with Pediococcus acidilactici, Enterococcus faecium and Lactobacillus plantarum with a final application rate of 165,000 cfu of lactic acid bacteria (LAB)/g of fresh forage weight (T1X), or the same inoculant with a final application rate of 330,000 cfu of LAB/g of fresh forage weight (T2X). After treatment, about 1 kg of forage was packed into 5 individually replicated nylon-polyethylene vacuum barrier bags for each treatment. Bags were evacuated of air and heat sealed. All silos were allowed to ferment at 21 ± 0.5°C for 3, 30, and 60 d. Data were analyzed using the Fit Model in JMP (SAS Institute Inc., Cary, NC) as a 3 ´ 3 factorial arrangement of treatments with the main effects of treatment (3), days of ensiling (3), and their interaction. Fresh alfalfa had a pH of 6.24 before ensiling. The pH of mDM silages treated with inoculants was lower (P < 0.01) than CN after 3, 30 and 60 d. Specifically, the pH at 3 d, for CN, T1X and T2X was 5.51, 5.17, and 5.11, respectively. In contrast, inoculation had no effect on pH drop 3 d in hDM silage and T2X treatment was lower (P < 0.01) in pH than both CN and T1X after 30 and 60 d. Changes in lactic acid closely reflected changes in pH. Acetic acid was lower (P < 0.01) in inoculated silages at 30 and 60 d compared with CN in mDM silages but were similar among treatments in hDM silages. Compared with CN inoculation had no effects on soluble protein (% of CP), NH3-N, and 24 h in vitro NDF-D, but concentration of total CP was higher (P < 0.01) in T1X (18.19%) and T2X (18.12%) than CN (17.94%). The inoculants used in this study stimulated the fermentation equally in mid-DM alfalfa silage, but a higher application rate was needed to show improvement in high-DM silage.