Observational study of the microbiome of perforated abomasal ulcers in unweaned beef calves in Canada

In western Canada, perforating abomasal ulcers (AU) are generally diagnosed postmortem in beef calves up to 2 months of age. Certain microbes have been associated with AU, but the evidence is circumstantial. Thus, analyzing the abomasal microbiome in calves with and without AU may provide insight into the etiology of the disease. Using 16S rRNA gene sequencing, abomasal tissues from Western Canadian beef calves, with (n = 27) and without AU (n = 17), were analyzed for microbial diversity. No significant differences were seen between microbiomes of AU and CON calves despite numerical differences in abundance. Therefore, a subsample of 18 tissues (12 AU, 6 CON) were analyzed using untargeted metagenomic sequencing for determination of phylogeny, and the presence of antimicrobial resistance genes (ARGs). Staphylococcaceae (1.5%), Campylobacteraceae (1.4%) and Enterobacteriaceae (1.4%) were seen across all samples. Differential abundance analysis revealed Streptomyces spp. REN17 to be less abundant in AU calves, suggesting a potential association between Streptomyces spp. and calf gut health. An ARG associated with polymyxin resistance was found to be differentially abundant in calves with a history of antimicrobial therapy. Although differences were observed in the predicted metabolic functions among groups, none reached statistical significance. In our study, no consistent microbial signature associated with AU was identified, despite the differential abundance of individual taxon, nor did prior antimicrobial therapy associate to the growth of specific microbiota. To better understand the potential role of the abomasal microbiota in AU etiology and the impact of early life interventions in beef calves, a larger sample size is needed.