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Longitudinal shifts in the rumen bacterial communities of dairy cows during the transition period
The transition period in dairy cows refers to the period three weeks prior to calving to three weeks post-calving and is critical for sustained milk production and animal health. We evaluated the rumen microbial dynamics in primiparous and multiparous cows during their transition period. In the current study, ten animals from primiparous (n=5) and multiparous groups (n=5) were randomly selected based on the freshening date (expected date for parturition). Each animal was sampled for rumen contents by stomach tube, two hours after feeding, at four time points i.e., three weeks prior to the anticipated freshening date (S1), soon after the animal freshened (S2), four weeks (S3) and eight weeks (S4) into lactation. Both groups received the same dry cow ration (CP-14.65%; NDF-43.66%; Starch-21.9%) prior to calving and the same lactating cow ration (CP-17.21%; NDF-33.14%; Starch-27.19%) post calving. The genomic DNA form rumen samples was extracted and amplified using the primers BSF8 (27F) and BSR357 annealing to the V1-V2 region of the 16S rDNA bacterial gene. The amplicon libraries were sequenced on a 454 Jr Roche platform and analyzed for bacterial diversity using QIIME. A total of forty bacterial communities were analyzed that involved annotations of 100,000 reads, which were assigned to 15,861 operational taxonomic units (OTU). Bacterial community comparisons were based on the UniFrac distance metric which revealed that both study group and study day had an independent effect on the community compositions (P<0.05; Permanova test). The most abundant phyla observed were Bacteroidetes and Firmicutes across all communities. As the cows transitioned into lactation, the ratio of Bacteroidetes to Firmicutes increased from 6:1 to 12:1 (P<0.05; Mann-Whitney U test) and this ratio was higher in primiparous than in multiparous animals (P<0.05). This study elucidated distinct shifts in the rumen microbiome confounded by dietary and physiological changes in both primiparous and multiparous dairy cows in their transition period. However, validating these results using more animals per lactation group is warranted.
Keywords: Dairy cows, Transition period, Rumen bacteria, Pyrosequencing, 16S pyrotags