Effects of daytime or night-time grazing on animal performance, diurnal behaviour and enteric methane emissions from dairy cows at high latitudes

This study compared animal performance and enteric methane (CH4) emissions from dairy cows in a part-time grazing (PTG) system in northern Sweden. Twenty-four Nordic Red dairy cows were allocated to one of two treatments: DAY (10 h daytime pasture access) or NIGHT (12 h night-time pasture access). The cows in each treatment received the same ad libitum partial mixed ration (PMR) indoors and ad libitum herbage allowance. Methane was recorded using two linked GreenFeedTM emissions monitoring (GEM) units, on pasture and indoors. Day or night grazing showed no statistical differences in estimated grass or PMR intake, milk production or daily enteric CH4 emissions. There was a rapid decrease in diurnal CH4 emissions (28%) when the cows were moved from indoors to pasture in both grazing treatments. Using two GEM units (indoor, outdoor) in combination improved the diurnal assessment of enteric CH4 emissions during PTG conditions in the mixed feeding system.