Effect of enriched biochar on methane emissions, rumen microbial structure and rumen fermentation characteristics in Holstein steers

• Enriched biochar did not reduce methane emissions from Holstein steers. • Body weight and intake not affected with dietary biochar addition. • Solid and liquid associated ruminal microbes differed. • Enriched biochar increased abundance lachnospiraceae and runinococcaceae families. • Fermentation end products were not affected by dietary strategy. Nutritional strategies, such as oil inclusion or addition of 3-Nitrooxypropanol, to reduce methane emissions from ruminants show promise, but have not been as effective in low quality or roughage based diets. The objective of this study was to investigate the effect of enriched biochar on methane production and fermentation characteristics in an oaten hay diet. This study used a 3 × 3 Latin square design, where 3 fistulated Holstein steers (790 ± 100 kg initial body weight) were fed a basal diet of oaten hay, with either 1) oaten pellets (Control), 2) Oaten pellets containing biochar at 1 % of dietary DM; or 3) Oaten pellets containing enriched biochar at 1 % DM. Each period lasted for 21 d, including 14 d dietary adaptation and 7 d experimental measurement. Rumen samples were collected on d 17–21 for determination of liquid and solid associated microbes, and rumen fermentation characteristics. The sulphur hexafluoride (SF 6 ) tracer technique was used to quantify methane emissions. Body weights (kg), dry matter and organic matter intakes (DMI and OMI), methane production (g/d), methane intensity (g kg -1 BW) and methane yield (g kg -1 DMI) were similar ( P ≥ 0.12) across the three treatment groups. Similarly, total VFA concentration and individual percentages of VFA were similar across treatments ( P ≥ 0.16). Microbes in the solid and liquid fractions showed little differences among treatments ( P ≤ 0.049) indicating that biochar included in an oaten hay diet, whether standard or enriched, had little effect on rumen fermentation, microbial communities or methane emissions in Holstein steers.