The objective of the study was to determine the circadian variation in CH4 emission from cattle fed ryegrass-based pasture offered in two meals a day and identify factors that affect this circadian variation. Methane emission data (expressed as g/d) of 15 respiration chamber trials with growing beef cattle (six trials) or non-lactating (three trials) and lactating (six trials) dairy cows was analysed. 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; P < 0.05) and within the growing and non-lactating cattle dataset, the ratio also correlated negatively with forage neutral and acid detergent fibre concentration (r = -0.74; P < 0.10) and positively with crude protein concentration (r = 0.77; P < 0.10). In summary, the magnitude of circadian variation in CH4 emissions decreased with increasing feeding level over the whole dataset and also with changing pasture composition within the growing and non-lactating animal dataset.
Proceedings of the New Zealand Society of Animal Production, Volume 79, Palmerston North, 61-64, 2019
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