Effects of post-pyrolysis treated biochars on methane production, ruminal fermentation, and rumen microbiota of a silage-based diet in an artificial rumen system (RUSITEC)

•Biochar did not affect rumen fermentation and nutrient disappearance.•Biochar had no effect on total gas and methane production.•Biochar did not affect protozoa populations and microbial protein synthesis.•Biochar had no effect on rumen microbiota diversity and richness. This study investigated the effects of including biochars, which differed in post-pyrolysis treatment, on nutrient disappearance, total gas and methane (CH4) emissions, rumen fermentation, microbial protein synthesis and rumen microbiota in an artificial rumen system (RUSITEC) fed a barley silage-based diet. The basal diet contained (g/kg dry matter (DM) basis); 600 barley silage, 270 barley grain, 100 canola meal and 30 mineral/vitamin supplement. Three spruced-based biochars were treated post-pyrolysis with either zinc chloride, a hydrochloric acid/nitric acid mixture or sulfuric acid and each included at 20 g/kg of diet DM. Treatments were assigned to sixteen fermenters (n = 4/treatment) in two RUSITEC units in a randomized complete block design. The experiment was conducted over 15 d, with 8 d of adaptation and 7 d of sampling and data collection. Nutrient disappearance of DM, organic matter (OM), acid detergent fiber (ADF), nutrient detergent fiber (NDF) and starch were determined after 48 h of incubation from d 9–12, and microbial protein synthesis was measured from d 14−15. Data were analyzed using PROC MIXED in SAS, with fixed effects of treatment and day of sampling (repeated measure) and random effects of RUSITEC unit and fermenters. Biochar inclusion did not affect disappearance of DM (P = 0.49), OM (P = 0.60), CP (P = 0.47), NDF (P = 0.48), ADF (P = 0.11) or starch (P = 0.58). Moreover, biochar inclusion did not affect total gas production (P = 0.31) or CH4 produced expressed as mg/g of DM incubated (P = 0.74), and mg/g (P = 0.64), or mg/d (P = 0.70) of DM disappeared. Compared to the control, there was a tendency (P = 0.06) for reduced CH4 production with biochar inclusion when CH4 was expressed as percent of total gas produced. Biochar inclusion did not affect total VFA (P = 0.56) or NH3-N (P = 0.20) production. Microbial protein synthesis was not affected by biochar inclusion (P > 0.05). Total protozoa counts were also unaffected by biochar (P = 0.37) nor did it impact (P > 0.05) the alpha or beta diversity of bacterial populations. In conclusion, the biochars evaluated in this study appeared to have little to no impact on nutrient disappearance, total gas and CH4 productio