| Summary: | Emission of enteric methane (CH4) from ruminants have become a growing concern for policymakers globally as CH4 now account for 6% of global greenhouse gas (GHG) emissions and the warming effect in the atmosphere is 28 times that of carbon dioxide (CO2). The Norwegian agricultural sector has made an agreement with the government to reduce GHG emissions by 5 million tonnes of CO2 equivalents from 2021 to 2030, and improved forage quality is one of the main strategies to achieve this reduction. Grass-clover silage constitutes a large part of ruminant diets in Northern and Western Europe, as well as in North America. Timothy (Phleum pratense L) has been the dominating perennial grass species in Norway, Sweden, Finland and Iceland for centuries, but as climate is getting warmer perennial ryegrass (Lolium perenne L) species has become more commonly used, especially in the coastal areas with mild winters. Due to increased temperatures and extended growing season, it is now possible to increase the number of cuts per season, and increased harvest frequency is already used as a strategy to harvest high quality forage for ruminants. However, the impact of silage chemical composition, ley species, harvest frequency, wilting, fermentation pattern, and use of mixed silages from different cuts on in vitro and in vivo CH4 production is largely unknown. Therefore, the overall objective of this doctoral thesis was to develop strategies in silage production to mitigate enteric methane emissions from ruminants. We aimed to identify the quality attributes of grass and clover silage associated with variation in in vitro CH4 production, and to test the effects of grassland species, cutting frequency, wilting and fermentation pattern on in vitro CH4 production. Further, we aimed to investigate the effect of ley species (timothy, perennial ryegrass and red clover) and cutting frequency (two vs. three cuts per season) on dry matter intake (DMI), milk production and CH4 production in lactating dairy cows. In Paper I we found that among ...
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