The structural and functional capacity of ruminal and cecal microbiota in growing cattle was unaffected by dietary supplementation of linseed oil and nitrate

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Popova, Milka | Mcgovern, Emily | Mccabe, Matthew | Martin, Cécile | Doreau, Michel | Riquelme, Marie | Meale, Sarah Jade | Morgavi, Diego | Waters, Sinead

Edité par CCSD ; Frontiers Media -

Microorganisms in the digestive tract of ruminants differ in their functionality and abilityto use feed constituents. While cecal microbiota play an important role in post-rumenfermentation of residual substrates undigested in the rumen, limited knowledge existsregarding its structure and function. In this trial we investigated the effect of dietarysupplementation with linseed oil and nitrate on methane emissions and on the structureof ruminal and cecal microbiota of growing bulls. Animals were allocated to either aCTL (control) or LINNIT (CTL supplemented with 1.9% linseedand 1.0% nitrates) diet.Methane emissions were measured using the GreenFeed system. Microbial diversity wasassessed using amplicon sequencing of microbial genomic DNA. Additionally, total RNAwas extracted from ruminal contents and functionalmcrAandmttgenes were targetedin amplicon sequencing approach to explore the diversity offunctional gene expressionin methanogens. LINNIT had no effect on methane yield (g/kg DMI) even though itdecreased methane production by 9% (g/day;P<0.05).Methanobrevibacter-andMethanomassiliicoccaceae-related OTUs were more abundant in cecum (72 and 24%)compared to rumen (60 and 11%) irrespective of the diet (P<0.05). Feeding LINNITreduced the relative abundance ofMethanomassiliicoccaceae mcrAcDNA reads inthe rumen. Principal component analysis revealed significant differences in taxonomiccomposition and abundance of bacterial communities between rumen and cecum.Treatment decreased the relative abundance of a fewRuminococcaceaegenera, withoutaffecting global bacterial community structure. Our research confirms a high level ofheterogeneity in species composition of microbial consortia in the main gastrointestinalcompartments where feed is fermented in ruminants. There was a parallel between thelack of effect of LINNIT on ruminal and cecal microbial community structure and functions differences in Rumen and Cecum Microbiomeson one side and methane emission changes on the other. These results suggest thatthe sequencing strategy used here to study microbial diversity and function accuratelyreflected the absence of effect on methane phenotypes in bulls treated with linseed plusnitrate.

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