A longitudinal characterization of the seminal microbiota and antibiotic resistance in yearling beef bulls subjected to different rates of gain

Authors: WEBB, EMILY - North Dakota State University; HOLMAN, DEVIN - Agriculture And Agri-Food Canada; SCHMIDT, KAYCIE - North Dakota State University; Crouse, Matthew; DAHLEN, CARL - North Dakota State University; Cushman, Robert - Bob; Snider, Alexandria - Alex; MCCARTHY, KACIE - University Of Nebraska; AMAT, SAMAT - North Dakota State University

Submitted to: Microbiology Spectrum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2023
Publication Date: 3/14/2023
Citation: Webb, E.M., Holman, D.B., Schmidt, K.N., Crouse, M.S., Dahlen, C.R., Cushman, R.A., Snider, A.P., McCarthy, K.L., Amat, S. 2023. A longitudinal characterization of the seminal microbiota and antibiotic resistance in yearling beef bulls subjected to different rates of gain. Microbiology Spectrum. 11(2). Article e05180-22. https://doi.org/10.1128/spectrum.05180-22.
DOI: https://doi.org/10.1128/spectrum.05180-22

Interpretive Summary: Increasing evidence supports the existence of a microbial community in bovine semen, and that this seminal microbiota may influence not only the male reproductive health, but also female and offspring health through microbial transfer. In this study, we evaluated the seminal and fecal microbial population in yearling beef bulls fed a common diet to achieve moderate (1.13 kg/d) or high (1.80 kg/d) rates of weight gain. Semen samples were collected on days 0 and 112 of the feeding trial as well as post-breeding. There was no difference by dietary treatment in the seminal plasma or fecal microbial populations. The seminal plasma microbial population was distinct from the fecal microbiome with only 6% of population shared between the two collection sites. Our culturing results revealed that bovine semen harbors not only commensal bacteria, but also potential bacterial pathogens that are associated with bovine respiratory disease, liver abscesses and reproductive infections, mastitis, and lameness in cattle. This data supports the need to identify how the male microbial population in semen interacts with the female reproductive tract and affects pregnancy success.

Technical Abstract: In this study, we evaluated the seminal and fecal microbiota in yearling beef bulls fed a common diet to achieve moderate (1.13 kg/day) or high (1.80 kg/day) rates of weight gain. Semen samples were collected on days 0 and 112 of dietary intervention (n = 19/group) as well as postbreeding (n = 6/group) using electroejaculation, and the microbiota was assessed using 16S rRNA gene sequencing, quantitative PCR (qPCR), and culturing. The fecal microbiota was also evaluated, and its similarity with seminal microbiota was assessed. A subset of seminal bacterial isolates (n = 33) was screened for resistance against 28 antibiotics. A complex and dynamic microbiota was detected in bovine semen, and the community structure was affected by sampling time (R2 = 0.16, P < 0.001). Microbial richness increased significantly from day 0 to day 112, and diversity increased after breeding (P > 0.05). Seminal microbiota remained unaffected by the differential rates of gain, and its overall composition was distinct from fecal microbiota, with only 6% of the taxa shared between them. A total of 364 isolates from 49 different genera were recovered under aerobic and anaerobic culturing. Among these seminal isolates were pathogenic species and those resistant to several antibiotics. Overall, our results suggest that bovine semen harbors a rich and complex microbiota which changes over time and during the breeding season but appears to be resilient to differential gains achieved via a common diet. Seminal microbiota is distinct from the fecal microbiota and harbors potentially pathogenic and antibiotic-resistant bacterial species. IMPORTANCE Increasing evidence from human and other animal species supports the existence of a commensal microbiota in semen and that this seminal microbiota may influence not only sperm quality and fertility but also female reproduction. Seminal microbiota in bulls and its evolution and factors shaping this community, however, remain largely underexplored. In this study, we characterized the seminal microbiota of yearling beef bulls and its response to the bull age, different weight gains, and mating activity. We compared bacterial composition between seminal and fecal microbiota and evaluated the diversity of culturable seminal bacteria and their antimicrobial resistance. Our results obtained from sequencing, culturing, and antibiotic susceptibility testing provide novel information on the taxonomic composition, evolution, and factors shaping the seminal microbiota of yearling beef bulls. This information will serve as an important basis for further understanding of the seminal microbiome and its involvement in reproductive health and fertility in cattle.