Circadian variation in methane emissions by cattle fed ryegrass-based pasture

The objective of the current study was to determine the circadian variation in CH4 emission from cattle fed ryegrass-based pasture offered in two meals a day. Methane emission data (expressed as g/d) of 15 respiration chamber trials with growing beef cattle (6 trials) or non-lactating (3 trials) and lactating (6 trials) dairy cows was used for the current analysis. Minimum CH4 production rate, measured approximately every 3 minutes, in the 24 h day, among the 15 trials ranged from 51 g/d to 217 g/d, and maximum CH4 production rate ranged from 152 g/d to 471 g/d. The ratio of maximum to minimum CH4 production rate, indicating absolute circadian variation, among the 15 trials ranged from 1.8-fold to 4.4-fold. This ratio correlated negatively with feeding level (r = 0.57) and within the growing and non-lactating cattle, the ratio also correlated negatively with forage fibre (neutral and acid detergent fibre) concentrations (r = 0.60 to 0.70). In summary, the magnitude of circadian variation in CH4 emissions decreased with increasing feeding level and also with increasing pasture fibre concentrations in growing and non-lactating animals.