Factors Affecting Ratios of C02: CH4 in Bovine Rumen Gas

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Abstract
Aliquots of bovine rumen gas collected continuously were analyzed at intervals during the digestive cycle. Gas composition varied in a regular manner with the time from feeding. The ratio of CO2:CH4 was narrowest after fasting (1:1), and was widest (3:1) within 2 hr. after feeding. Following this peak, the ratio narrowed until 4 hr. after feeding, when it widened again to a secondary peak. Thereafter, the CO2:CH4 ratio gradually narrowed to that of the fasting level. Similar patterns were obtained when the ration was either hay and concentrate or concentrate alone. The widest ratios of CO2:CH4 were obtained when the ration included roughage. Although terpenes inhibited in vitro methane formation from acetate, the addition of D-limonene to feed to give estimated concentrations of 9 x 10-4 M, 1.8 x 10-3 M, or 3.6 x 10-3 M in the rumen had no effect on in vivo methanogenesis. Continuous sparging of the rumen ingesta with free H2, to the extent that the rumen gas contained 22% H2, had no effect on rumen methanogenesis as measured by the ratios of CO2 to CH4 in the rumen gas. Apparently H2 is the limiting factor in rumen methanogenesis.

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