Short communication: Variability in fermentation end-products and methanogen communities in different rumen sites of dairy cows.

The objective of this study was to investigate differences in fermentation and methanogen communities in samples collected from 3 sites in the rumen of dairy cows. The study involved 3 ruminally cannulated nonlactating Chinese Holstein dairy cows fed a diet of 40% forage and 60% concentrate feeds. Four handfuls of whole ruminal contents were collected from the cranial sac, middle of the ventral sac, and caudodorsal blind sac of the rumen of the cows at 0, 2.5, and 6 h after the morning feeding. Concentrations of VFA, ammonia, and dissolved methane and hydrogen were analyzed. Methanogen populations and communities were analyzed targeting 16s rRNA genes. Dissolved methane concentration and pH were highest in samples from the cranial rumen. Ruminal fluid from the cranial rumen also had greater copy numbers of the Methanobrevibacter and higher Simpson indexes compared with samples from middle of the ventral rumen. In summary, cranial rumen had higher dissolved CH4 concentration than middle and hind rumen, which might be caused by the greater population of Methanobrevibacter with higher ruminal pH.