Enteric methane emission of the Dutch dairy herd: Average and variation of enteric methane emission among the Dutch dairy herd

The Netherlands aims to reduce greenhouse gas emissions by 49% in 2030 compared to 1990. In order to achieve this goal the dairy sector needs to reduce methane (CH4) emissions by 1.0 megaton CO2-equivalents compared to 2017. Approximately 80% of the CH4 emission of the dairy sector originates from enteric CH4. The objectives of this study were therefore: 1) To gain insight into the average enteric CH4 emission and variation of the Dutch dairy herd, 2) to investigate which factors have an influence on the variation, and 3) to compare the measured CH4 emission per farm to the estimated emission using model calculations. In total CH4 production was successfully measured from 791 dairy cows (996 records) of 18 farms throughout the Netherlands for a period of 2 weeks from September 2018 to October 2019 using Greenfeed (C-lock Inc.). The average CH4 production was 437±94 g CH4/cow/day and per kg fat-protein corrected milk 14.4±5.1 g CH4/kg FPCM. According to the Linear Mixed Model analysis fitted with Restricted Maximum Likelihood 49% of the total variation was explained by farm and animal factors: soil type (6%), grazing related to season (3%), lactation stage and parity (32%), the content of urea and lactose in the milk and the lactation value (together 8%). Feed composition and feed quality components did not show a significant effect on the observed variation. A comparison of the average herd emission of single farms revealed no correlations between the CH4 emission measured in this inventory and estimated using model calculations. Further research is required on the effects of fresh grass as well as fresh grass quality, rumen microbiome or genetics on CH4 emission.