Browsing by Author "Urich, Tim"

In spring dairy cows are often gradually transitioned from a silage-and concentrate-based ration (total mixed ration, TMR) to pasture. Rumen microbiota adaptability is a key feature of ruminant survival strategy. However, only little is known on the temporal and spatial microbial alterations involved. This study aims to investigate how the rumen liquid (LAAB), particle (PAAB), and epithelium (EAAB) associated archaea and bacteria are influenced by this nutritional change. A 10-wk trial was performed, including 10 rumen-fistulated dairy cows, equally divided into a pasture-and a confinement-group (PG and CG). The CG stayed on a TMR-based ration, while the PG was gradually transitioned from TMR to pasture (wk 1: TMR-only, wk 2: 3 h/day on pasture, wk 3 & 4: 12 h/day on pasture, wk 5-10: pasture-only). In wk 1, wk 5, and wk 10 samples of solid and liquid rumen contents, and papillae biopsies were collected. The DNA was isolated, and PCR-SSCP and 16S rRNA gene amplicon sequencing analysis were performed. Cluster analysis revealed a higher similarity between LAAB and PAAB, compared to the EAAB, characterized by higher species diversity. At all three locations the microbiota was significantly influenced by the ration change, opposite the generally acknowledged hypothesis that the EAAB remain more consistent throughout dietary changes. Even though the animals in the PG were already on a full-grazing ration for 4-6 days in wk 5, the microbiota at all three locations was significantly different compared to wk 10, suggesting an adaptation period of several days to weeks. This is in line with observations made on animal level, showing a required time for adaptation of 2-3 weeks for production and metabolic variables. A large part of the rumen prokaryote species remained unaltered upon transition to pasture and exhibited a strong host influence, supporting the hypothesis that the rumen microbiota consists of a core and a variable microbiota. For the effect of the location as well as the ration change either very similar or opposite trends among member species of common taxa were observed, demonstrating that microbes that are phylogenetically close may still exhibit substantially different phenotypes and functions.

In response to oral application, monensin alters the rumen microbiota, increasing ruminal propionate production and energy availability in the animal. Data from different studies indicate that the susceptibility of rumen bacteria to monensin is mainly cell-wall dependent but tracing its activity to specific microbial groups has been challenging. Several studies have shown a similar effect for essential oils but results are inconsistent. To investigate the influence of monensin and a blend of essential oils (BEO, containing thymol, guaiacol, eugenol, vanillin, salicylaldehyde, and limonene) on the rumen microbiome, rumen liquid samples were collected orally on d 56 postpartum from cows that had either received a monensin controlled-release capsule 3 wk antepartum, a diet containing a BEO from 3 wk antepartum onward, or a control diet (n = 12). The samples were analyzed for pH, volatile fatty acid, ammonia, and lipopolysaccharide concentrations and protozoal counts. A 16S rRNA gene fingerprinting analysis (PCR-single-strand conformation polymorphism) and sequencing revealed that the BEO treatment had no effect on the rumen microbiota, whereas monensin decreased bacterial diversity. Twenty-three bacterial species-level operational taxonomic units were identified for which monensin caused a significant decrease in their relative abundance, all belonging to the phyla Bacteroidetes (uncultured BS11 gut group and BS9 gut group) and Firmicutes (Lachnospiraceae, Ruminococcaceae, and Erysipelotrichaceae). Ten bacterial operational taxonomic units belonging to the phyla Actinobacteria (Coriobacteriaceae), Bacteroidetes (Prevotella), Cyanobacteria (SHA-109), and Firmicutes (Lachnospiraceae and Ruminococcaceae) increased in relative abundance due to the monensin treatment. These results confirm the hypothesis that varying effects depending on cell-wall constitution and thickness might apply for monensin sensitivity rather than a clear-cut difference between gram-negative and gram-positive bacteria. No effect of monensin on the archaea population was observed, confirming the assumption that reported inhibition of methanogenesis is most likely caused through a decrease in substrate availability, rather than by a direct effect on the methanogens. The data support the hypothesis that the observed increase in ruminal molar propionate proportions due to monensin may be caused by a decrease in abundance of non-producers and moderate producers of propionate and an increase in abundance of succinate and propionate producers.