Effects of administration of live or inactivated virulent Rhodococccus equi and age on the fecal microbiome of neonatal foals.
Authors: Bordin Angela I, Suchodolski Jan S, Markel Melissa E, Weaver Kaytee B, Steiner Jörg M, Dowd Scot E, Pillai Suresh, Cohen Noah D
Journal: PloS one
Summary
# Editorial Summary: *Rhodococcus equi* and the Neonatal Foal Microbiome Enteral administration of live *Rhodococcus equi* has shown promise as a mucosal immunisation strategy to protect foals against subsequent respiratory challenge, yet little was known about how such exposure—or inactivated variants—might reshape the developing intestinal microbiome during this critical early-life window. Bordin and colleagues administered either live virulent *R. equi* (10¹⁰ CFU) or inactivated *R. equi* (2×10¹⁰ and 10¹¹ CFU) to neonatal foals and tracked changes in faecal microbiota composition across the first month of life using molecular sequencing. Age emerged as the dominant driver of microbiome change during this period, with the microbial community shifting progressively regardless of treatment; however, foals receiving live *R. equi* showed distinct alterations in specific bacterial populations compared to controls and inactivated-treatment groups. These findings suggest that live attenuated or virulent organisms may meaningfully influence not just mucosal immunity but also the broader intestinal ecosystem during critical developmental stages. For practitioners considering mucosal immunisation protocols or interpreting foal gut health, this work highlights the need to consider how early microbial exposures shape microbiome trajectory—a factor that may have downstream implications for digestive function, pathogen colonisation resistance, and immune development.
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Practical Takeaways
- •Live R. equi enteral administration may work partly through microbiome modulation; timing of administration during the critical first weeks of life appears important for establishing protective immunity
- •Understanding that foal intestinal microbiomes naturally shift during the first month can help inform optimal timing and dosing strategies for oral immunization protocols
- •Inactivated R. equi at higher doses produces different microbiome effects than live vaccine—practitioners should consider which formulation better matches farm disease challenges and foal age at treatment
Key Findings
- •Fecal microbiome composition changes significantly with age during the first month of life in foals
- •Administration of live virulent R. equi (1×10¹⁰ CFU) altered fecal microbiome structure differently than inactivated R. equi at higher doses
- •Enteral administration of R. equi modulates intestinal microbial communities in neonatal foals, potentially supporting mucosal immune development
- •Age-related microbiome changes occur independently of R. equi exposure in the first month of life