Repeatability of enteric methane measurements using GreenFeed systems on upland pastures

Plant diversity of mountain pasture has been shown to reduce enteric methane (CH4) production in vitro. In 2023, we set up an in vivo experiment to measure enteric CH4 emission using GreenFeed (GF) systems and dairy performances of 28 grazing dairy cows on mountain pasture. After 3 weeks of being fed fresh grass indoor, they were taken out to extensively managed pasture for 9 weeks. Cows were allowed to graze large areas (from 1 to 3.5 ha), and 2 GF equipped with solar panels were accessible near the water trough. As lower frequency of animal visits to the GF at pasture than indoor was expected, our aim was to determine the minimum number of consecutive CH4 spot measurements (CSM) to achieve a good repeatability of CH4 data. As expected, the average number of visits per animal and per day (d) was 2.6 ± 0.42 vs 0.7 ± 0.24 during indoor vs grazing periods. Five to 20 CSM were randomly chosen within the set of available data per animal per period (indoor vs outdoor) and the draws were repeated 10 times. The analysis was repeated 5 times to evaluate the consistency of the results across draws. Results showed that a minimum of 15 CSM acquired in 12 and 29 d was necessary to achieve a similar repeatability of 0.53 and 0.50 indoor vs at pasture, respectively, with a low variability across repetitions and no effect of the interval between first and last CSM. If performances of GF measurement indoor or in small plots of intensive pasture are documented, it is the first time at our knowledge that their performances were studied under extensive grazing conditions on natural grasslands in Europe.