The presence of oxygen in rumen liquor and its effects on methanogenesis

In situ measurement of O 2 in the rumen liquor of cows, sheep and goats using a membrane‐covered O 2 electrode revealed the presence of up to 1630 nmol/l O 2 ; O 2 became undetectable immediately after feeding of animals. The effects of O 2 on H 2 production and methanogenesis in samples of rumen liquor were investigated using a mass spectrometer fitted with a membrane inlet system. Methanogenesis was totally and irreversibly inhibited after short term exposure (about 10 min) to 5 KPa (0·05 atm) O 2 ; H 2 production was unaffected. Glucose additions produced rapid transient increases in H 2 levels and increased O 2 uptake.