Effect of spruce (Picea abies) biochar on ruminal dry matter digestibility and methane production in vitro | Kuusen (Picea abies) biohiilen vaikutus pötsin kuiva-aineen sulavuuteen ja metaanin tuotantoon in vitro

Biochar, produced by heating biomass in oxygen-limited environments, is known for its potential to reduce methane emissions, by altering rumen fermentation. However, the literature lacks exploration on how biochar affects nutrient digestibility and ruminal methane production across various diets. Therefore, we examined the effects of spruce (Picea abies) biochar on several forage plant species options and forage-to-concentrate (F:C) ratios. Two in vitro trials of 24 hours were conducted with Gas Endeavour® equipment at Animal Science laboratory of the University of Helsinki. There were three rumen fluid donor animals and the ratio of rumen fluid and McDougall’s buffer was 1:2 (vol:vol). The first trial tested biochar levels (0%, 0.25%, and 0.5% of diet dry matter (DM)) with four silage options that were pure grass (Phleum pratense – Festuca pratensis), grass mixed 1:1 in DM with red clover (Trifolium pratense), faba bean (Vicia faba), or maize (Zea mays L) at a fixed F:C ratio of 65:35. The concentrate consisted of oats and rapeseed meal. The second trial explored the effects of the biochar (0.5% of diet DM) and an alternative methane inhibitor (product X) alone or combined across 65:35 and 45:55 F:C ratios. Key parameters such as total gas and methane production, DM digestibility, rumen fluid pH, and volatile fatty acid (VFA) concentrations were analyzed. Grass silage (D-value 669, neutral detergent fiber (NDF) 523 g/kg DM) and red clover silage (D-value 626, NDF 362 g/kg DM) were harvested from the first cut. Maize silage was more digestible than faba bean silage (D-value 679 vs. 593 g/kg DM) and contained more starch (278 vs. 48 g/kg DM). High forage diet (65:35) had higher NDF content (453 vs 407 g/kg DM) and lower starch content (114 vs 179 g/kg DM) than low forage diet (45:55). Biochar's effect on DM digestibility and the production of rumen methane or carbon dioxide was not significant across different silage plant species and F:C ratios. Grass silage led to lower total methane production compared to silage mixtures (p<0.05), and the combination of biochar and product X in a low forage diet numerically reduced gas production. However, when methane production was calculated per digested DM, no differences were observed. Feeding maize silage increased the total production of methane and carbon dioxide in the rumen compared to faba bean silage (p<0.001), but gas productions per digested DM remained unaffected. Biochar did not significantly affect final rumen pH across silage species. Biochar with grass silage linearly reduced the total VFA content of the rumen fluid (p=0.003) and had tendency for smaller molar proportion of acetic acid in VFA (p= 0.075). In the second trial biochar or product X didn´t have significant effect on rumen fermentation pattern across forage levels. The effects of biochar, silage plant species and F:C ratios on in vitro rumen fermentation and methane production were minimal, despite differences in diet composition.