Respiration chamber is the frequently employed technique for measuring enteric CH₄ emission in ruminants. However, the rate of CH₄ emissions changes throughout the day, and the interval time between measurements usually miss maximum and minimum values and may affect the estimation of CH₄ emissions.

Researchers from China Agricultural University and the Institute of Subtropical Agriculture (ISA) of the Chinese Academy of Sciences investigated the evaluation of measurement interval and calculation method for the quantification of enteric methane emissions measured by respiration chamber. Their findings were published in Journal of Dairy Science. 

Scientists found that the 23-h kinetics of CH₄ emissions and rates of CH₄ emissions varied widely among 10 cows, and the amount of 23-h CH₄ emissions was positively correlated with body weight and age of cows. The rates of CH₄ emissions ranged from 4.6 to 11.4 g/h throughout the day. The maximum rate occurred about 1 to 2 h after feeding, and then it gradually declined to the basal level.

When animals were fed twice per day, two distinct peaks were observed in the diurnal kinetics of CH₄ emissions. However, when increasing the measurement interval, diurnal kinetics of CH₄ emissions changed significantly.

Furthermore, increased interval significantly decreased maximum rate of CH₄ emission and increased its minimum rate. When interval was increased from 0.5 to 180 min, the calculated amount of 23-h CH₄ emissions was not affected.

Although measuring CH₄ concentrations at different intervals missed the maximum and minimum values in the kinetics of CH₄ emissions, the missed maximum and minimum values might offset each other, leading to the unchanged estimate of total CH₄ emissions.

When interval was extended to 4 h, the calculated amount of 23-h CH₄ emissions were significantly increased in comparison to the estimate at 0.5 min intervals.

This study indicated that increasing the interval between measurements may lead to an underestimate of maxima and an overestimate of minima with respect to the pattern of daily enteric CH₄ emissions, but does not affect the estimate of 23-h CH₄ emission if the interval between measurements is less than or equal to 3 h.

The research was supported by the National Key Research and Development Program of China, National Natural Science Foundation of China, State Key Laboratory of Animal Nutrition, Hunan Province Science and Technology Plan, China Agriculture Research System, Youth Innovation Promotion Association CAS, and CAS President’s International Fellowship.