Evaluating the inoculating bacterial communities within the bovine neonatal respiratory tract after applying an ablation technique to the dam vaginal microbiota prior to parturition.

The vaginal microbiota (VM) is the neonate's first microbial exposure, playing a role in early health outcomes. However, the impact of VM disruption at parturition on neonatal microbial inoculation and passive transfer success remains unclear. Betadine lavages (BL) are commonly used to control reproductive tract infections but can induce microbial dysbiosis. Disrupting the VM before calving may reduce microbial competition during colonization, increasing the risk of pathogen establishment. This study aimed to determine whether VM dysbiosis affects neonatal bacterial communities and passive transfer in beef cow-calf pairs. Cows (n = 12) were randomly assigned to a control group (CON) or BL treatment group (BLG) 2 wk before calving. BLG cows received 1 to 2 treatments based on calving date. Samples (dam colostrum, calf sera, dam-vaginal swab, dam-udder swab, dam-haircoat swab, and calf-nasal swab) were collected within 24 h of birth and stored at -80 °C. The V3-V4 region of the 16S rRNA gene was sequenced using Illumina MiSeq. Alpha diversity was assessed via 2-way ANOVA, β-diversity via PERMANOVA, and taxonomic differences via LEfSe. IgG concentrations in calf serum and colostrum were analyzed using ELISA. Data were evaluated using the R software package (v. 2023.03 + 386). BL-induced VM dysbiosis did not alter α-diversity in the dam-vaginal (P = 0.42), dam-udder (P = 0.53), or dam-haircoat (P = 0.21) microbiota but did affect the calf-nasal microbiota (P = 0.03). Beta diversity was unchanged in the dam-vaginal (P = 0.66) and dam-udder (P = 0.56) microbiota but trended toward greater variation in BLG calf-nasal (P = 0.08) and dam-haircoat (P = 0.09) samples. BLG calves exhibited an increased relative abundance of the phylum Actinobacteria and decreased relative abundance of the phylum Proteobacteria in the nasal microbiota compared with CON calves. Passive transfer status did not differ between groups (P = 0.88), but BLG dams had higher colostrum IgG concentrations than CON dams (P = 0.04), suggesting an immune response to pre-calving microbial disruption. Together, these results are indicative of microbial dysbiosis prior to parturition, leading to an increased immune response in BLG dams, which altered colostrum IgG. Thus, dam colostrum composition could drive immune responses against neonatal inoculating bacteria, resulting in differing nasal microbial communities between BLG and CON calves.