Determination of enteric methane emissions of dairy cows fed with different diets and relationship with milk yield and ruminal function in order to improve advice for farmers

Methane from ruminal fermentation, termed enteric methane, contributes 40% of the total agricultural emissions (Gerber et al., 2014). Mitigation of methane production could allow for a reduction in the impact of livestock on climate change and may improve the public perception towards this sector. Milk yield, methane emissions, carbon footprint and dietary costs were measured in experimental and commercial farms in different diet conditions: enriched fat diet (linseed or canola), high concentrate diet, high level of starch in diet or grazing. Individual milk samples were analysed monthly for milk quality and for methane emissions predicted by milk spectra analysis. The first results showed that methane emissions per kg of milk can vary from 11 to 20 g. Preliminary comparison between the diets demonstrated that feeding with grazed grass was beneficial in terms of feeding costs and environmental impact while methane emissions per kg milk were higher. Diets with low fibre content can have a beneficial impact to decrease methane emissions but could disturb ruminal function. These results will allow us to predict methane emissions and environmental impacts of milk production according to the diet composition, dietary costs, lactation stage and milk production. From these results, advice about feeding strategies could be given to reach the best compromise between environmental and economic objectives.