Impact of Storage Temperature and Aerobic Exposure Time on the Fermentation Characteristics and Mycotoxin Levels of Re-Ensiled Corn Silage

Re-ensiling is an important practice in the commercialization and transportation of high-quality silage, yet limited information is available regarding its effectiveness under different storage temperatures and aerobic exposure times. This study aimed to evaluate the effects of storage temperature and aerobic exposure time on the fermentation characteristics, chemical composition, and mycotoxin levels of re-ensiled corn silage. Whole-plant corn harvested at the dough stage (39.77% DM) was initially stored at 20 °C, 30 °C, and 40 °C for 90 d and subsequently subjected to 0, 48, 72, and 96 h of aerobic exposure before re-ensiling, with three replicates per treatment. The results showed that corn silage initially stored at 20 °C and re-ensiled within 48 h of aerobic exposure exhibited the lowest pH (3.70), highest lactic acid concentration (56.78 g/kg DM), and highest Flieg score (99.67) among all temperature treatments (p > 0.05). In contrast, corn silage initially stored at 40 °C and re-ensiled after 96 h of aerobic exposure retained higher water-soluble carbohydrate (5.47% DM) and crude protein (7.32% DM) contents (p > 0.05). Aerobic exposure increased concentrations of beauvericin (71.89–864.92%), zearalenone (6.24–24.20%), and alternariol (0.77–1.89%) across all storage temperatures. Following 96 h of aerobic exposure, re-ensiling reduced these mycotoxin concentrations by 3.16–67.32%, 9.10–20.57%, and 0.62–6.79%, respectively. Overall, re-ensiling helped to preserve silage quality after aerobic exposure. The greatest benefits were observed when silage initially stored at 20 °C was re-ensiled within 48 h, while re-ensiling after prolonged exposure effectively mitigated mycotoxin risks.