Influence of Growth Stages and Additives on the Fermentation Quality and Microbial Profiles of Whole-Plant Millet Silage

This study aimed to determine the optimal growth stage and additives for producing high quality millet silage through two experiments. Experiment 1: Whole-plant millet from the same field and under uniform management was harvested at the heading, sizing, milking, dough, and full-maturity stages. Then, it was chopped into 2–3 cm segments, vacuum-sealed in plastic bags without any further treatment, stored at 20 °C, and opened after 60 days. The results indicated that the dough stage had the highest water-soluble carbohydrate (WSC) and crude protein (CP) contents. The lactic acid (LA) and acetic acid (AA) contents during the dough and maturity stages were significantly higher than other stages, with the lowest pH observed during the dough stage. Experiment 2: The whole-plant millet was harvested at the dough stage. It was then chopped into 2–3 cm segments using a forage chopper, mixed thoroughly, and subjected to different treatments—inoculation with 10⁶ CFU/g FM of <i>Lactiplantibacillus plantarum</i> (LP), adding of 1% FM sucrose (S), and a combination of <i>Lactiplantibacillus plantarum</i> and sucrose (MIX)—with a control group (CK) receiving an equivalent amount of water. The MIX treatment significantly enhanced the WSC content compared to other treatments (<i>p</i> < 0.05), and both the LP and MIX treatments showed superior LA and AA contents and lactic acid bacteria counts. These additives significantly altered the bacterial community, shifting dominance from Proteobacteria in the CK and raw materials to Firmicutes. <i>Klebsiella</i> dominated the CK group but was significantly reduced in the additive treatments, where <i>Lentilactobacillus</i> became the dominant genus. Therefore, we recommend harvesting millet at the dough stage and adding a mixture of <i>Lactiplantibacillus plantarum</i> and sugar to improve fermentation quality and aerobic stability.