Changes in microbial population in the rumen of sheep fed Acacia mearnsii tannin extract for methane reduction

Abstract

Methane (CH4) is one of the primary gases that contribute to global warming. It is a by-product of enteric fermentation of ruminant animals, which is produced by microbes (methanogens that belong to domain Archaea) in the rumen. The emission of methane from the ruminant can be reduced to varying degrees through the manipulation of the rumen microbiome by various dietary interventions. It has been well established that diet affects the microbial community structure and composition. Tannins have been shown to directly or indirectly inhibit methanogenesis, thereby reducing methane. However, the effect of encapsulated tannins on the microbial diversity in the rumen has not been fully understood. In this study, 24 rumen samples were analysed from a study where Eragrostis curvula based diet was fed to South Africa Mutton Merino sheep, and was supplemented with tannin crude or encapsulated tannin. DNA were extracted and sequenced using shotgun metagenomic and analysed using MG-RAST. Out of the 28 bacteria phyla identified by shotgun sequencing, Bacteroidetes (72%) and Firmicutes (21%) were the dominant phyla. A total of 500 bacterial genera were recorded, where Prevotella, Bacteroides, Eubacterium and Clostridium had the highest abundance. Forty-one archaeal genera were identified with Methanobrevibacter having the highest abundance. However, the total bacteria and total methanogen did not significantly differ between the tannin and non-tannin treatments. This shows that tannin in its crude or encapsulated form did not have any effect on the methane producing microbes and the overall microbial community.