Overdosing a Commercial Inoculant with Pediococcus pentosaceus, Lentilactobacillus buchneri, and Lentilactobacillus hilgardii Does Not Improve Acetic Acid Synthesis or Alfalfa Silage Aerobic Stability

During feedout, silage is exposed to air, promoting the growth of aerobic microorganisms that degrade its quality. Obligate heterofermentative lactic acid bacteria (LAB) can produce acetic acid, which enhances aerobic stability. Higher inoculation rates may further increase acid production. The goal of this study was to evaluate the aerobic stability of alfalfa silage (Medicago sativa L.) with increasing inoculant rates. Treatments included a control without inoculant (CON), the standard inoculation rate (SIC 1.0), 1.5× the standard rate (SIC 1.5), and 2.0× the standard rate (SIC 2.0). The inoculant contained Pediococcus pentosaceus, Lentilactobacillus buchneri, and Lentilactobacillus hilgardii with xylanase and beta-glucanase enzymes. Silages were prepared in five replicates per treatment (four for SIC 1.0) and aerated for seven days, during which fermentation characteristics and microbial populations were evaluated. Lactic acid was threefold higher in CON and SIC 2.0 than in SIC 1.0 and SIC 1.5 (p = 0.004), indicating unexpected homofermentative activity in SIC 2.0. All inoculated silages had greater acetic acid (38–51 g/kg DM) and propionic acid (0.83–4.05 g/kg DM) than CON (p < 0.001), but the highest acetic acid concentrations were observed in SIC 1.0 rather than at higher inoculant rates. Inoculation resulted in higher LAB counts (p < 0.001) and stable aerobic conditions; however, increasing the inoculant rate above the manufacturer’s recommendation did not enhance aerobic stability or acetic acid production. These results highlight that optimal inoculant dosing, rather than higher application rates, is critical for effective alfalfa silage preservation.