Tannin as a feed additive for mitigating enteric methane emission from livestock: meta-analysis from RUSITEC experiments

Abstract

A study was performed to evaluate the effect of dietary tannin on methane emission from livestock by using a meta-analysis method. A total of six rumen simulation technique (RUSITEC) experiments that composed of 25 treatments from published articles were integrated in a database. Parameters recorded were nutrient digestibility, total gas production, methane emission, volatile fatty acid (VFA) profiles, pH, ammonia concentration and microbial counts, i.e. total bacteria and protozoa. Data were statistically analyzed by using a mixed model methodology in which different studies were treated as random effects and dietary tannin was considered as fixed effect. Results revealed that methane emission decreased linearly with increasing level of dietary tannin (P < 0.01; R2 = 0.677). Tannin decreased nutrient digestibility, i.e. crude protein digestibility (P < 0.05; R2 = 0.407), neutral detergent fiber digestibility (P < 0.01; R2 = 0.411) and acid detergent fiber digestibility (P < 0.01; R2 = 0.543). Tannin generally did not alter VFA profiles, pH, ammonia concentration and microbial population in the RUSITEC system. It is concluded that increasing level of dietary tannin leads to a decrease in enteric methane emission from livestock. The decrease appears to be indirectly through reduction in digestibility of nutrients, particularly fiber, and directly through inhibition of archaea methanogen.