The Effect of Black Tea Lees on In vitro Rumen Fermentation Parameters and Methane Emissions

Abstract

Background and Objectives: Global efforts to mitigate methane emissions from ruminant livestock are critical for addressing climate change and enhancing feed efficiency. Black Tea Lees (BTL), a by-product rich in polyphenolic tannins, may serve as a functional feed ingredient to reduce enteric methane emissions. This study evaluated the effects of substituting oat hay with BTL at varying inclusion levels (0-30%) on in vitro rumen fermentation characteristics and methane production. Materials and Methods: Proximate composition, neutral detergent fiber, acid detergent fiber and acid detergent lignin of BTL was measured. Total extractable phenols, total extractable tannins and condensed tannins in the BTL were also analyzed. In vitro rumen fermentation was carried out to assess dry matter digestibility, methane production and organic acid production. Results: Chemical analysis revealed that BTL contained high levels of crude protein and tannins. Total gas production and methane yield (CH₄ per gram of digested dry matter) decreased significantly with increasing levels of BTL substitution. Notably, CH₄ production was significantly suppressed at 25 and 30% inclusion levels, though digestibility declined at these higher concentrations. Substitution at 5 and 10% reduced CH₄/DDM without negatively affecting dry matter digestibility. Organic acid profiles were altered, with reduced acetate and increased lactate observed in a dose-dependent manner. These findings suggest that low-level incorporation of BTL in ruminant diets may effectively reduce methane emissions while maintaining ruminal fermentation efficiency. Conclusion: The valorization of BTL thus offers a promising strategy to mitigate greenhouse gas emissions and support sustainable livestock production.