Characterisation of the faecal bacterial community in adult and elderly horses fed a high fibre, high oil or high starch diet using 454 pyrosequencing.
Authors: Dougal Kirsty, de la Fuente Gabriel, Harris Patricia A, Girdwood Susan E, Pinloche Eric, Geor Raymond J, Nielsen Brian D, Schott Harold C, Elzinga Sarah, Newbold C Jamie
Journal: PloS one
Summary
# Editorial Summary Seventeen horses aged 5–28 years were fed three sequential diets—forage alone, forage with starch-rich concentrate, and forage with oil-rich concentrate—to determine how supplementation and age alter the faecal microbiota using 454 pyrosequencing of 16S rDNA. Diet significantly shaped bacterial composition at the operational taxonomic unit (OTU) level, with 52 discriminatory OTUs identified; Firmicutes dominated the changes (37 OTUs), whilst the core microbiota shrank dramatically with supplementation (from 30 OTUs and 15.9% of sequences on forage alone to just 15 OTUs and 5.4% on the starch diet), suggesting that concentrates reduce microbial commonality across individuals. Elderly horses (19–28 years) exhibited reduced bacterial diversity compared to mature animals (5–12 years), though the overall community structure remained stable, mirroring patterns observed in human ageing. For practitioners, these findings emphasise that diet composition—particularly starch versus oil supplementation—produces measurable shifts in the hindgut microbiota; whilst age-related diversity loss appears clinically silent in healthy horses, supplementary feeding may necessitate individual microbiota management, especially when transitioning between forage-based and concentrates-supplemented programmes.
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Practical Takeaways
- •Starch-rich supplementation produces the most significant shift in hindgut bacterial composition; if using concentrates, oil-based supplements may be gentler on microbial stability than starch
- •Elderly horses naturally have lower bacterial diversity—monitor closely when changing diets in senior animals as their microbiome may be less resilient to dietary shifts
- •Individual variation in bacterial response to the same diet is substantial; what suits one horse's microbiome may not suit another, supporting the case for individualised feeding strategies
Key Findings
- •High starch supplementation reduced faecal bacterial core diversity to 5.4% of OTUs compared to 15.9% for forage alone, while high oil supplementation showed intermediate reduction to 10.3%
- •Elderly horses (aged 19-28) showed significantly reduced bacterial diversity compared to mature horses (aged 5-12), though community structure remained unchanged
- •Only 6 OTUs (2.3% of sequences) were common across all three diets, dominated by Clostridiales order and Lachnospiraceae family
- •Firmicutes phylum accounted for 37 of 52 significantly different OTUs across diets, with smaller changes in Bacteroidetes, Proteobacteria, Actinobacteria and Spirochaetes