Evaluation of the effects of green tea extract as a dietary supplement in sheep on gas production, volatile fatty acids, and digestibility

Background and Aim: Phenolic tannins, which are ubiquitous in plants, exhibit diverse biological activities and have drawn significant attention for their potential impact on ruminant nutrition and health. Although phenolic tannins have beneficial and detrimental effects on rumen fermentation, their precise influence remains poorly understood. This study aimed to explore the effects of varying doses of green tea extract (GTE) on rumen fermentation parameters through an in vitro trial using sheep rumen liquids. Materials and Methods: A 4 × 2 factorial design was used to test the effect of 4 different doses of GTE treatment (0, 140, 280, and 560 mg/kg) in 2 different in vitro runs on degradability, fermentation profiles, and gas production using the in vitro Hohenheim Gas Test method. Results: Across running times, the GTE-treated diet did not affect (p > 0.05) dry matter degradability % and organic matter degradability %, pH, ammonia (NH₃-N, mg/dL), 24 h total gas production (tGP 24h, mL), and acetate-to-propionate ratio (A: P), but it reduced (p < 0.05) tGP 6 h compared with GTE-0 (control diet without GTE). GTE treatment tended to reduce (p < 0.1) methane (CH₄, % LEL) and total volatile Fatty Acids (tVFA, mM). Across GTE treatment, the 1^st in vitro run had higher (p < 0.001) tGP 6–24 h and pH, but lower (p < 0.001) tVFA and A: P in comparison with the 2^nd in vitro run. Conclusion: GTE treatment tends to decrease CH₄ output in rumen without affecting degradability, tGP, and most fermentation profiles, except for a tendency to reduce tVFA.