Effect of conventional grain-fed and grass-fed feeding systems on fecal microbiota and shiga toxin-producing Escherichia coli in beef cattle

Summary

This study, published in BMC Microbiology in 2025, investigates how conventional grain-fed feedlot and grass-fed beef production systems influence the fecal microbiome and the carriage of Shiga toxin-producing Escherichia coli (STEC) in cattle. Using fecal sampling and likely 16S rRNA amplicon sequencing, the authors — affiliated with institutions including UC Davis given co-author James Oltjen's known affiliation — compare microbial diversity and pathogen risk across the two systems. The findings are likely to contribute evidence to ongoing debates about whether grass-fed production systems reduce or alter STEC shedding risk relative to grain-fed feedlot systems, with implications for food safety and livestock management.

UK applicability

Although conducted in the United States, the findings are broadly applicable to UK beef production, where both pasture-based and mixed grain-supplemented finishing systems are common; the results may inform UK food safety guidelines and farm assurance standards concerning STEC management in cattle.

Key measures

Fecal microbiota composition (16S rRNA sequencing, alpha and beta diversity indices); STEC prevalence and/or abundance; feeding system (grain-fed vs. grass-fed)

Outcomes reported

The study compared fecal microbial community composition and the prevalence or abundance of Shiga toxin-producing Escherichia coli (STEC) in beef cattle raised under conventional grain-fed (feedlot) versus grass-fed management systems. It likely assessed differences in microbiota diversity and STEC carriage rates between the two production systems.

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