Lower Methane Emissions from Yak Compared with Cattle in Rusitec Fermenters

Globally methane (CH(4)) emissions from ruminant livestock account for 29% of total CH(4) emissions. Inherited variation about CH(4) emissions of different animal species might provide new opportunity for manipulating CH(4) production. Six rumen-simulating fermenters (Rusitec) were set up for this study lasting for 16 d. The diet consisted of forage to concentrate ratio of 50:50 with barley straw as the forage. Treated vessels were supplied with rumen fluid from yak or cattle (3 vessels per animal species). Microbial growth was measured using (15)N as a marker. The microbial community structure from liquid- and solid-fraction of each vessel was determined based on the 16S rRNA genes targeting both bacteria and archaea with MiSeq platform. CH(4) yield was lower when the inoculum used from yak than that from cattle (0.26 and 0.33 mmol CH(4)/g dry matter intake, respectively). Lower H(2) production was observed in Rusitec fermenters with rumen fluid from yak compare with that from cattle (0.28 and 0.86 mmol/d, respectively). The apparent digestibility of neutral detergent fiber, the isovalerate percentage with respect to the total amount of volatile fatty acids, the hydrogen recovery, and the proportion of liquid-associated microbial nitrogen derived from ammonia-nitrogen were higher in Rusitec fermenters incubated with rumen fluid from cattle than that from yak. The relative abundances of methanogens were no difference between two animal species. We hypothesize that more H(2) production contributes to the higher methane emissions in cattle compare with yak.