Understanding interactions between diet, methane emissions and microbial community composition in growing and finishing beef cattle

Abstract Text:

At the heart of enteric methane production in ruminants is a microbial food chain.  The microscale processes of this microbial food chain are greatly influenced by diet.  The interactions between diet, microbial community composition and methane emissions are poorly understood.  To evaluate the influence of diet on microbial community composition and methane emission, 120 animals were fed 10 different growing and finishing diets.  Growing diets included high and low quality forage, with and without monensin supplementation, and different inclusions of modified distillers grain plus solubles (MDGS), and the finishing diets contained different fat sources (corn oil, tallow, and distillers) with and without monensin supplementation, and direct fed microbial (DFM).  Microbial community composition and methane emission was monitored.  Methane and CO₂ concentrations of respired air were taken during feeding in an individual feeding facility utilizing 120 individual bunks equipped with the Calan® gate system and an automated gas collection system.  Samples were analyzed using GC methods and CO₂ was used as the internal standard.  Methane:CO₂ ratio was used to measure dietary effects on methane emission.  Rumen fluid was collected via esophageal tubing for microbial community analysis.  The V3 region of the 16S rRNA gene was sequenced using the Ion Torrent personal genome machine (PGM).  On the common diet, microbial community structure and methane levels were similar across animals but changed when fed the growing and finishing treatment diets.  In growing diets, forage quality (high vs low) significantly influenced (P < 0.05) the CH₄:CO₂ ratio and the microbial community with cattle fed high quality forage producing lower methane per pound of gain.  The level of methane emitted was not affected by level of MDGS supplementation but significantly changed microbial community structure.  In finishing diets the source of fat, monensin supplementation and DFM had no effect on methane level.  However, level of MDGS supplementation affected microbial community structure.  These results indicate that dietary intervention strategies can be used to change microbial community structure and influence methane emissions in growing cattle.  Identification of microbial species in high and low methane-emitting cattle under different diets would help identify dietary factors that can be used to control methane emission from cattle.

Keywords: 16S rRNA, methane, microbial community.