Abstract
The rumen microbiome is fundamental for the productivity and health of dairy cattle and diet is known to influence the rumen microbiota composition. In this study, grape-pomace, a natural source of polyphenols, and copper sulfate were provided as feed supplementation in 15 Holstein-Friesian calves, including 5 controls. After 75 days of supplementation, genomic DNA was extracted from the rumen liquor and prepared for 16S rRNA-gene sequencing to characterize the composition of the rumen microbiota. From this, the rumen metagenome was predicted to obtain the associated gene functions and metabolic pathways in a cost-effective manner. Results showed that feed supplementations did alter the rumen microbiome of calves. Copper and grape-pomace increased the diversity of the rumen microbiota: the Shannon’s and Fisher’s alpha indices were significantly different across groups (p-values 0.045 and 0.039), and Bray-Curtis distances could separate grape-pomace calves from the other two groups. Differentially abundant taxa were identified: in particular, an uncultured Bacteroidales UCG-001 genus and OTUs from genus Sarcina were the most differentially abundant in pomace-supplemented calves compared to controls (p-values 0.003 and 0.0002, respectively). Enriched taxonomies such as Ruminiclostridium and Eubacterium sp., whose functions are related to degradation of the grape- pomace constituents (e.g. flavonoids or xyloglucan) have been described (p-values 0.027/0.028 and 0.040/0.022 in Pomace vs Copper and Controls, respectively). The most abundant predicted metagenomic genes belonged to the arginine and proline metabolism and the two- component (sensor/responder) regulatory system, which were increased in the supplemented groups. Interestingly, the lipopolysaccharide biosynthetic pathway was decreased in the two supplemented groups, possibly as a result of antimicrobial effects. Methanogenic taxa also responded to the feed supplementation, and methane metabolism in the rumen was the second most different pathway (up-regulated by feed supplementations) between experimental groups.
Highlights
The rumen microbiota is a preeminent microbial community in the gastrointestinal tract of ruminants
Sequencing the V3-V4 regions of the bacterial 16S rRNA gene produced a total of 8 393 698 reads
S3 Table reports reports the number of sequences before and after quality filtering using two quality thresholds: Phred > 3 and Phred > 19
Summary
The rumen microbiota is a preeminent microbial community in the gastrointestinal tract of ruminants. This finely regulated ecosystem is what makes it possible for ruminants to digest fibrous plant material (inedible for other livestock), use it as source of energy and other metabolites, and transform it into high-quality food. The rumen microbiome plays a key role in milk production [1], well-being and health of the animals [2, 3]. Feed supplementations had the objective of counteracting the effects of the high-energy diets typical of dairy cows on the rumen pH, the composition of the rumen microbiota, and the health of the animals. It is of interest to further investigate the role of these two feed supplements on the rumen microbiome composition and function
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