Lactobacillus casei TH14 and Hydrolysable Tannin as Corn Silage Additives Modify In Vitro Rumen Fermentation and Reduce Methane Production

This study evaluated L. casei TH14 (TH14) and two levels of hydrolysable tannin (HT; sweet chestnut, Castanea sativa) as corn ensiling additives, hypothesising that their combination would improve fermentation quality and reduce in vitro CH4. Whole-plant corn was ensiled for 21 days in a completely randomised design (seven treatments, four replicates) combining Molasses, TH14, and HT at 20 or 40 g/kg DM. Silage pH was significantly affected by treatment (p < 0.01), with T4 reaching the lowest final pH (3.83), whereas the primary nutrients (DM, OM, CP, and NDF) were unchanged (p > 0.05). Hydrolysable tannin reduced ruminal NH3-N at 24 h (11.12 vs. 13.06 mg/dL; p < 0.05) and, at 40 g/kg DM, lowered CH4 by 50.0% at 24 h (2.45 vs. 4.90 mL/g DM; p < 0.01) in a dose-dependent manner, accompanied by a higher propionate proportion and a lower acetate-to-propionate ratio (p < 0.01). Independent of tannin, TH14 reduced CH4 by 12.7% (p < 0.05). Digestibility was transiently reduced at 24 h but unaffected at 48 h (p > 0.05). Corn silage with HT at 40 g/kg DM, alone or combined with TH14, is a promising strategy to mitigate CH4 without impairing nutrient digestibility.