Vaginal microbiota and circulating interferon-stimulated genes in lactating dairy cows at and following time of artificial insemination.

Reproductive tract microbiota has been shown to shift during early gestation in cattle. However, characterization of the vaginal microbiota during the establishment of pregnancy in lactating dairy cows has yet to be fully determined. Therefore, the objectives of this study were to characterize shifts in the vaginal microbiota from time of artificial insemination (AI) to maternal recognition of pregnancy and analyze its relationship with interferon-stimulated genes (ISGs) in lactating dairy cows. Vaginal swab samples for microbiota analysis and blood were collected from lactating Holstein dairy cows (n = 40) on day 0 (d0; time of AI) and day 18 (d18; post-AI during the time of maternal recognition of pregnancy). Pregnancy status was determined via transrectal ultrasonography on d32 (Open, n = 18 and Pregnant, n = 22). Microbiota analysis for phylum and genus taxonomic classification, as well as α- and β-diversity, was conducted targeting the V4 hypervariable region of the 16S rRNA gene on d0 and d18. RT-qPCR analysis was conducted to analyze expression of ISGs, interferon-stimulated gene 15 kDa (ISG15) and myxovirus resistance 2 (MX2), on d0 and d18. Phyla and genera greater than 1% relative abundance did not differ between Open and Pregnant cows (P > 0.10). Shifts in certain bacterial phyla and genera between d0 and d18 (P < 0.05), along with lower α-diversity matrices of Simpson's diversity index (P = 0.02) and Shannon's diversity index (P = 0.009) on d18, indicate that time-dependent shifts in bacterial communities may alter reproductive success. This is further supported by the difference between days for the weighted UniFrac β-diversity matrix (P = 0.005). Reduced MX2 expression on d18 (P = 0.002), and its correlation with Fusobacteria (r = -0.35; P = 0.09), may be indicative of pregnancy failure and thus result in Open cows. These results indicate that shifts in microbiota from day of AI to d18 may influence successful establishment of pregnancy in lactating dairy cows.