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Influences of feeding behaviour and forage quality on diurnal methane emission dynamics of grazing cows

Abstract:

This study aimed to evaluate diurnal methane (CH 4 ) emission dynamics of grazing cattle and highlight their relationships with biotic factors such as the feeding behaviour as well as seasonal changes in pasture characteristics. Existing methods to assess grazing ruminants’ daily CH 4 emissions provide useful insights to investigate mitigation strategies relying on feeding and genetic selection. Nonetheless such methods based on tracer gases (SF 6 ) or feeding bins equipped with sniffers (e.g. GreenFeed) can hardly cover diurnal CH 4 emission fluctuations which can influence the accuracy of total CH 4 production estimations. Previous studies in barns showed that emission dynamics strongly vary during post feeding time, leading to a possible bias in estimates of daily CH 4 emissions as high as 100%. To investigate whether such fluctuations are also taking place on pasture, a portable device was designed with infrared CH 4 and CO 2 sensors measuring concentrations in the exhaled air at a high sampling rate (4 Hz). Six grazing dry red-pied cows were equipped with the device and motion sensors during runs of 24h to monitor CH 4 and CO 2 emissions and detect their feeding behaviours (grazing, rumination and other behaviours), respectively. This experiment was performed in summer and fall in order to cover seasonal changes in pasture forage quality. Methane emission was estimated from the CH 4 :CO 2 concentration ratio and the metabolic CO 2 production of the cows. As for barn studies, variations were observed in total daily CH 4 emission due to the seasons and diurnal variations were also observed due to animal behaviours. Relationships between animal feeding behaviour and CH 4 emissions patterns on pasture were also unravelled.