Effect of Aerobic Exposure on Microbial Community Changes and Mycotoxin Content Changes in Corncob Silage

This study aimed to investigate the effects of different aerobic exposure durations on mycotoxin accumulation, nutritional quality changes, and microbial community dynamics of corncob silage. The experiment was divided into four groups: T0 (corncob silage fermented for 45 days without aerobic exposure), T4 (corncob silage exposed to air for 4 days), T8 (corncob silage exposed to air for 8 days), and T12 (corncob silage exposed to air for 12 days). The results showed that after aerobic exposure, the contents of dry matter (DM), crude protein (CP), water-soluble carbohydrates (WSC), Crude Ash, lactic acid (LA), and ammonia nitrogen (NH3-N) in all exposed groups (T4, T8, T12) were significantly lower than those in the T0 group, whereas the contents of neutral detergent fiber (NDF), acid detergent fiber (ADF), propionic acid (PA), and butyric acid (BA) were significantly higher than those in the T0 group. Exposure to aerobic conditions for 12 days resulted in the four mycotoxins exhibiting levels significantly higher than those in the other groups, and notably, zearalenone (ZEN) and ochratoxin (OT) exhibited a continuous increase in concentration with the extension of aerobic exposure. Aerobic exposure increased bacterial diversity and fungal relative abundance, and significant separations were observed in both bacterial and fungal communities between the T0 group and the aerobic exposure groups. At the phylum level, Firmicutes was the dominant bacterial phylum in the T0 group, while Pseudomonadota became the dominant phylum after aerobic exposure. At the genus level, Lacticaseibacillus was the dominant bacterial genus in the T0 group, whereas Variovorax, Vibrionimonas, and Mycobacterium dominated the bacterial communities in the aerobic exposure groups. The relative abundance of the fungal phylum Ascomycota increased from 30% in the T0 group to 80~90% in the aerobic exposure groups; the dominant fungal genera shifted from Zygosaccharomyces to Albifimbria and Pichia. In conclusion, prolonged aerobic exposure elevates the concentrations of mycotoxins in corncob silage, reduces the nutritional quality, and induces significant shifts in both bacterial and fungal community compositions.