Dietary biochar as a feed additive for increasing livestock performance: A meta-analysis of in vitro and in vivo experiment

The present study aimed to evaluate the use of biochar as a feed additive on nutrient utilization and livestock performance by employing a meta-analysis method. Various in vitro and in vivo studies regarding the effects of biochar on rumen fermentation, nutrient disappearance, total gas, methane production, microbial population, feed intake, growth performance, blood constituents, nutrient digestibility and nitrogen retention were tabulated in a database. Data were analysed using the mixed model method in which the different studies were considered as random effects while the biochar addition was treated as a fixed effect. The addition of biochar reduced methane production (quadratic pattern; P < 0.05), but increased the total gas production (P < 0.001). Addition of biochar decreased (quadratic pattern; P < 0.05) volatile fatty acids and acetic acid in the in vitro rumen fermentation data. In the in vivo data, a reduction in feed conversion ratio (quadratic pattern; P < 0.05), as well as a reduction (P < 0.05) in the feed intake parameters of dry matter, organic matter, crude protein, and neutral detergent fibre were observed with biochar addition. Ammonia production and propionic acid tended to increase linearly (P < 0.05) with the biochar supplementation. The biochar supplementation increased (P < 0.05) the nutrient digestibility (dry matter, organic matter, crude protein, neutral detergent fibre) and nitrogen retention. In conclusion, biochar supplementation of ruminant diet modulates rumen fermentation by increasing propionic acid but decreasing methane emissions, and enhances livestock performance by increasing nutrient digestibility, growth performance as well as nitrogen retention.