Predicted methane production from Italian ryegrass pastures with contrasting chemical composition under sheep grazing in Northern Norway

Background The Norwegian sheep farming system relies on forages, such as grass silage during winter and grazing cultivated leys and rangeland pastures during summer. Sheep and other ruminants produce enteric methane (CH 4 ), a greenhouse gas of interest, and there is a need for reliable data on gas emissions from sheep capturing both the indoor feeding period and the grazing season. This study utilized an in vitro gas technique (with standard cow rumen fluid) and modeling approach to estimate CH 4 production and fermentation patterns based on two different qualities of Italian ryegrass ( Lolium multiflorum ) pasture under sheep grazing. Results Herbage quality was examined for two 10‐day periods, in July and August. Differences in chemical composition of the herbage during these periods had an impact on herbage digestibility and CH 4 production. Total gas production and CH 4 levels were significantly higher for lower quality herbage grazed in July than for higher quality herbage grazed in August ( p < 0.005). Production of volatile fatty acids in the rumen remained constant between the two periods, but the higher acetate to propionate (A/P) ratio correlated with the higher CH 4 production. Conclusion These findings suggest that pasture quality is an important factor to consider when implementing grazing strategies to reduce enteric CH 4 production in sheep.