Relationship between daily variations of methane emissions and eructation peaks in dairy cows measured with an automated head-chamber system

Enteric methane (CH4) is primarily produced by methanogens during microbial fermentation in the rumen and is subsequently eructated through the oral and nasal passages of ruminants. As such, the present study hypothesized that the rates and daily amounts of CH4 emission may be closely associated with CH4 eructation peaks. To test this hypothesis, 12 dairy cows (6 lactating and 6 non-lactating) were selected as experimental animals with contrasting daily enteric CH4 emissions. The experiment was conducted in two phases, with six non-lactating dairy cows in phase 1 and six lactating dairy cows in phase 2. For each phase, CH4 eructation peaks were monitored every 2 h interval to calculate diurnal CH4 emissions, with 12 time points scattered in four consecutive days by an automated head-chamber (AHC) system. The measurements were repeated, and total period of measurements lasted for 16 consecutive day. The results showed that compared with non-lactating dairy cows, lactating dairy cows exhibited greater diurnal CH4 emissions and rates of CH4 emission, together with higher peak frequency (P = 0.002), peak height (P < 0.001) and peak area integral (P < 0.001). Moreover, the rates of CH4 emission was not constant and exhibited a fast increments after feeding, and had a positive correlation (R2 ≥ 0.54, P < 0.001) with peak height of CH4 eructation. In conclusion, these findings indicate that the varied rates of CH4 emission among dairy cows can be caused by altering peak frequency and peak area integral of CH4 eructation, while a diurnal change in rates of CH4 emission is associated with peak area integral through altering the peak height of CH4 eructation.