Eating Pattern, Rumen Fermentation, and Microbial Population in Dairy Cows Exhibiting Divergent Methane to Carbon Dioxide Ratio in Breath

This study aimed to elucidate the association of methane (CH₄) production with eating behavior, rumen fermentation, and the rumen microbial population among dairy cows with varying CH₄ to carbon dioxide (CO₂) ratios in their breath, as measured by the sniffer method. Eighteen lactating Holstein cows were divided into three groups: low (LEm), mid (MEm), and high (HEm) CH₄:CO₂ ratios. Estimated CH₄ production was lower in the LEm group than in the HEm group. Daily dry matter intake and milk production did not differ among the groups, whereas body weight was lower in the LEm group than in the MEm group. Eating time tended to be longer at night for the LEm group than for the HEm group. The ruminal molar proportion of acetate was lower, whereas that of propionate was higher in the LEm group than in the HEm group. Additionally, bacteria producing lactate and succinate were more prevalent in the LEm group, which may be associated with the higher ruminal propionate and lower estimated CH₄ production in the LEm group. These findings suggest that body weight and eating time may be linked to variations in CH₄:CO₂ ratios in the respiration gases of cows that have the distinct rumen microbial community.