Efficacy of tannins as silage additives to inhibit deamination process during ensiling: a meta-analysis and in silico approach

Ensiling, the anaerobic preservation of forage, is widely used to ensure year-round feed availability. However, high-protein forages are prone to protein degradation and deamination during ensiling, leading to ammonia formation and reduced feed quality. This study evaluated the efficacy of tannins as natural additives for inhibiting protein deamination using a meta-analysis of published studies, complemented by an in silico approach. Because tannins possess protein-binding properties, their potential role in inhibiting deamination was further examined through interactions with glutamate dehydrogenase (GDH), an enzyme associated with deamination pathways in Clostridium species commonly found in silage. A random-effects meta-analysis was conducted using OpenMEE, and molecular docking simulations were performed using AutoDock4 to predict the binding affinity of tannin-derived compounds toward GDH. The meta-analysis showed that tannin supplementation significantly (p < 0.001) reduced NH₃-N, non-protein nitrogen (NPN), and soluble nitrogen concentrations, while also lowering butyric acid concentration, indicating improved silage quality. Meta-regression analysis further demonstrated a linear decrease in ammonia concentration with increasing tannin levels (equation: -0.842 - 0.048 × level). MM/GBSA analysis further suggested that terflavin B was the most stable ligand, with the lowest binding free energy (-51.06 kcal/mol), followed by corilagin (-43.11 kcal/mol) and punicalin (-34.48 kcal/mol), indicating strong interactions with the GDH active site. In addition, bioavailability and toxicity prediction indicated generally favorable safety characteristics of these tannin-derived compounds. Overall, the integrated findings support the potential of tannins as bioactive agents for reducing protein degradation in silage, thereby improving nutrient preservation and feed quality during storage.