An evaluation of the methane output associated with high-moisture grains and silages using the in vitro total gas production technique

Abstract

This study aimed to quantify the methane and total gas emissions associated with a range of ensiled feeds using the in vitro total gas production (TGP) technique. This suite of feeds included cereal grains (wheat, barley and triticale) and maize, whole-crop wheat and grass silages. The methane and total gas output of these feeds was then regressed on chemical composition to assess the relationship between these variables. Subsequently, the efficacy of the TGP technique was also discussed. From this analysis it was observed that 96% of the variation in methane output per unit of feed incubated was explained by variations in in vitro organic matter digestibility (IVOMD), neutral detergent fibre (NDF) and ash. Of these variables, the greatest single response was with NDF, which was negatively related to methane output. When expressed per unit of feed digested, 78% of the variation was explained by IVOMD, NDF and starch. The methane responses observed in this study contradicted expected in vivo trends in methane output, thus calling into question the reliability of the in vitro technique to accurately determine methane output of feeds differing this widely in NDF and starch contents.