Laboratory and field scale: two approaches for the evaluation of GHG emissions from dairy cows

The agricultural sector is an important contributor to emissions of greenhouse gases (GHG). At global scale GHG emissions from agricultural systems are estimated at 10-12% of the total anthropogenic. Modifying the diets of the dairy cows is a possible way to mitigate the emissions. Besides the methane (CH4) emissions from enteric fermentation, also the nitrous oxide (N2O) emissions from feed production have to be considered.This study (INNO-Mil-CH4) aims to evaluate the GHG emissions in dairy farms, through the analysis of the effect of different diets on the emissions from dairy cows at laboratory scale and the use of a model to estimate the GHG emissions at real farm conditions. Twenty dairy cows were fed with four diets different for fiber and starch content and the addition of extruded linseed. CH4 emissions were measured in respiration chambers. In parallel, at field scale, data on cow diets, manure management, fertilization and milk production were collected from 21 farms located in three regions in Germany over a period of 24 months. CH4 and N2O emissions for each farm were estimated, and the effects of the dietary components and the farm management were evaluated and correlated to the emissions.The results confirmed that CH4 emissions are strongly affected by the dry matter intake (DMI) and the linseed supplementation. A lower fiber and higher starch content in the diet reduced CH4 emission per kg milk by ~ 14%. The linseed supplementation (~ 8% of DMI) decreased CH4 emission per kg milk by ~ 12%. CH4 from enteric fermentation ranged between 12 and 15 g kg-1 milk-1 measured in the respiration chambers, and between 13 and 25 g kg-1 milk-1 estimated for the farm data. N2O emissions from feed production on the dairy farms ranged between 0.37 and 0.90 g kg-1 milk-1