| Ruminal methanogenesis is a microbial fermentive process conducted by methanogens, releasing methane (CH4) gas through eruction, and resulting in a dietary energy loss to the host animals and a contribution to greenhouse gas emissions by the agricultural industry. However, the association amongst methanogenic ecology, host feed efficiency, and host enteric CH 4 production is not clear. The overall objective of this research was to investigate the potential linkage among these sectors, and thus four studies were performed. Study 1 and Study 2 were conducted to investigate the correlation between cattle's feed efficiency and methanogenic ecology under growing and finishing diets. The composition of the methanogenic community varied significantly between the two diets, and the associations between methanogenic phylotypes and host's feed efficiency differed between the two diets. When animals were fed growing diet, Methanobrevibacter sp. AbM4 and Methanosphaera stadtmanae were more prevalent in inefficient animals; while under a finishing diet, multiple unidentified species were more common in inefficient animals. In Study 3, the correlation between methanogenic ecology and host CH4 production were studied in dairy cows, and the dietary effect on such correlation was also analyzed. Phylotypes resembling methanogenic archaeon CH1270 and Mbb. gottschalkii strain HO tended to be related to host's CH4 production, but the total methanogen population was not related to the amount of CH4 yield. In Study 4, host effect on ruminal methanogenic community and its adaptation to dietary treatments was examined in beef heifers. The unique microbiota of each animal and the distinctive responses to the dietary treatments within individuals indicate that the animal-to animal variation may be the main cause leading to the inconsistency of host response to dietary or environmental changes. Therefore, individual variation should be taken into account when studying ruminal microbial ecology. In summary, this research revealed that biodiversity of methanognic community rather than then total methanogen density plays an important role in affecting host feed efficiency, determining host's enteric CH4 production, and adapting to different dietary conditions. Furthermore, host is an essential factor determining its symbiotic relationship with methanogens. |
