Inhibition of rumen methanogenesis by tea saponins with reference to fermentation pattern and microbial communities in Hu sheep

Abstract

Twelve rumen fistulated Hu sheep were used to assess effects of tea saponins (TS) on methanogenesis, fermentation pattern and rumen microbial communities. All sheep were defaunated by administration of sodium lauryl sulfate. After two weeks, half of the defaunated sheep were refaunated by inoculation with faunate rumen fluid. Both defaunated (DfN) and refaunated (RfN) sheep were divided into two groups, and assigned to treatments in a 2×2 factorial arrangement without (RfN, DfN) or with TS (3g/d) (RfTs, DfTs). After a feeding period of 3wk, CH4 production of individual sheep was measured using open circuit respiratory chambers and rumen fluid was sampled for analysis of rumen fermentation products and extraction of microbial DNA. Numbers of gene copies associated with rumen methanogens (mcrA gene), specific bacteria (16S rDNA gene) and rumen protozoa and fungi (18S rDNA gene) were measured using real time ploymerase chain reaction (rt-PCR). The abundance of marker gene-copy number for the methanogens, protozoa, fungi, Ruminococcus albus, R. flavefaciens, Fibrobacter succinogenes and Butyrivibrio fibrisolvens were expressed relative to the copy number of total rumen bacterial 16S rDNA. Denaturing gradient gel electrophoresis was completed for protozoa to indicate the change in their diversity due to TS addition and defaunation. Declines in CH4 production as a result of addition of TS (2.1L/d, P<0.01) were similar to defaunation (2.5L/d, P<0.01). Compared to RfN, ammonia N concentrations were 12.9, 31.2 and 33.9% lower (P<0.01), whereas microbial protein concentrations were 16.4, 29.2 and 36.0% higher (P<0.01) in RfTs, DfN and DfTs, respectively. In contrast, the concentration of volatile fatty acids was similar among treatments although the molar proportion of propionate was higher (P<0.01) in defaunated sheep. The abundance of fungi and R. flavefaciens marker genes relative to total bacterial 16S rDNA were decreased by defaunation, and abundance of F. succinogenes declined (P<0.01) with either defaunation or addition of TS. The relative abundance of methanogen marker gene was reduced by defaunation (P<0.05). Protozoal abundance in RfTs was lower than that of RfN (P<0.05). The TS reduced (P<0.05) protozoal diversity. Addition of TS reduced CH4 production mainly by inhibiting protozoa, increasing molar proportions of propionate and decreasing acetate/propionate ratio without adversely altering relative ruminal abundance of fungi and cellulolytic bacteria.This article is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.