Effect of Harvest Time and Packing Density on the Quality and Clostridium in Maize Silage

This study investigated whole-plant maize at three harvest stages: one-third milk line (ML, 1/3 ML), two-thirds ML (2/3 ML), and the mature stage. Two packing densities were applied: 350 kg/m³ (low-density group) and 700 kg/m³ (high-density group). Results showed that starch content increased significantly as the maize matured. The 2/3 ML stage exhibited a 34.0% increase in starch content compared to the 1/3 ML stage (27.96 g/kg dry matter: DM vs. 20.87 g/kg DM, <i>p</i> < 0.01), while the mature stage showed a 13.4% increase compared to the 2/3 ML stage (31.70 g/kg DM vs. 27.96 g/kg DM, <i>p</i> < 0.01). After 60 days of ensiling, DM loss was significantly lower in the high-density group compared to the low-density group (3.37% vs. 9.39%, <i>p</i> < 0.05). From day 7 to day 60 of fermentation, the lactic acid content in the high-density group was consistently higher than in the low-density group by 14.29%, 10.00%, 8.33%, and 9.68%, respectively (<i>p</i> < 0.01). The relative abundance of <i>Clostridium</i> in both groups gradually increased during the first 30 days of fermentation, peaking on day 30 (0.05% in the high-density group vs. 0.12% in the low-density group, <i>p</i> < 0.05), and declined thereafter. On day 30, the abundance of <i>Ruminiclostridium</i> was significantly lower in the high-density group compared to the low-density group (0.12% vs. 0.40%, <i>p</i> < 0.05). <i>Clostridium</i> was negatively correlated with lactic acid bacteria (R² = -0.58, <i>p</i> < 0.01). It also showed negative correlations with pH, lactic acid, and acetic acid (R² = -0.25, -0.23, and -0.09, respectively; <i>p</i> > 0.05), but a positive correlation with ammoniacal nitrogen (R² = 0.28, <i>p</i> > 0.05). In conclusion, the 2/3 ML stage is the optimal harvest time for whole-plant maize. Additionally, a higher packing density can suppress spoilage-associated <i>Clostridium</i> and enhance silage quality.