Interactions entre le microbiote fécal et les chevaux athlètes

Interactions between fecal microbiota and athletic horses



Context and Objectives

The gut microbiota is recognized as a central player in regulating the physical, metabolic, and mental health of mammals. In horses, although studies have explored the effects of diet or exercise on intestinal microbial composition, few have simultaneously integrated environmental, physiological, and behavioral variables in a longitudinal approach. This study aims to fill that gap by analyzing the interactions between fecal microbiota, riding conditions, hematological parameters, and behaviors indicative of well-being in 185 athlete horses monitored over eight months.

Methodology

The horses, housed in the same national riding school in France, underwent two sampling campaigns (T1 and T2, spaced eight months apart). Fecal samples were analyzed using high-throughput sequencing of the V3–V4 region of the 16S rRNA gene. In parallel, 41 environmental and individual variables were measured, including:

  • Riding discipline and specialization
  • Type of bedding
  • Feeding data
  • Stereotypic behaviors (cribbing, weaving, aggression, hypervigilance)
  • Hematological parameters (MCHC, RWR, etc.)
  • Fecal pH and microbial loads (bacteria, protozoa, fungi)

Main Results

1. Structure and Dynamics of the Microbiota

  • High interindividual variability: Microbial composition differed more between individuals than within the same individual over time, especially for rare bacteria.
  • Stable microbial core: A set of 29 bacterial genera, mostly from the phylum Firmicutes, constituted the “core microbiota,” present in 99% of samples.
  • Temporal dynamics: A significant shift in microbial composition was observed between T1 and T2, with an increase in alpha diversity (Chao1, Fisher) and an overrepresentation of certain rare genera (e.g., Anaeroplasma, Enterococcus, Erysipelotrichaceae).

2. Factors Influencing Microbial Composition

Multivariate analysis revealed that six variables together explained 32% of the beta diversity variance:

  • Riding specialization (6.5%)
  • Discipline (5.8%)
  • Type of bedding (5.2%)
  • Hypervigilance (4.9%)
  • MCHC (6%)
  • Erythrocyte/leukocyte ratio (RWR) (5.7%)

Horses engaged in physically and mentally demanding disciplines (Gala, Cadre Noir) showed more homogeneous microbiota, suggesting a structuring effect of chronic stress.

3. Behavior and Microbiota

Significant correlations were established between certain behaviors indicative of poor welfare and microbial composition:

  • Oral stereotypies: associated with an overabundance of Roseburia, Acinetobacter, Desulfurispora, Helicobacter
  • Aggression: correlated with Streptococcus and Butyrivibrio, and inversely with Anaeroplasma
  • Hypervigilance: tended to be associated with Denitrobacterium and Dehalobacterium
  • Withdrawal from environment: linked to Diplorickettsia, Anaerorhabdus, Novosphingobium

These associations support the hypothesis of a functional gut–microbiota–brain axis in horses.

4. Microbiability of Traits

The concept of microbiability (m²), analogous to genetic heritability, was used to estimate the proportion of phenotypic variance explained by the microbiota:

Behaviors:

  • Oral stereotypies: 24.2%
  • Locomotor stereotypies: 16.2%
  • Aggression: 13%
  • Hypervigilance: 9%

Hematological parameters:

  • Eosinophils: 32.1%
  • RWR: 25.7%
  • Hemoglobin: 21.9%

Discussion

The results show that even under homogeneous housing conditions, the gut microbiota of athlete horses is influenced by factors related to training intensity, behavioral stress, and certain physiological markers. Horses subjected to high physical and mental loads exhibit microbial alterations consistent with a state of dysbiosis, which may be reversible.

The study suggests that the microbiota may not only reflect the state of well-being but also actively contribute to it through neuroendocrine and immune mechanisms. Butyrate-producing (Roseburia) or H₂S-producing (Desulfurispora) bacteria may play a protective role against the effects of chronic stress.

Conclusions and Perspectives

This pioneering study highlights the importance of the gut microbiota in regulating the behavioral and physiological well-being of athlete horses. It opens promising perspectives for:

  • Developing microbial biomarkers of stress and well-being
  • Using targeted probiotics to improve stress resilience
  • Integrating microbiota into breeding and management programs for sport horses

Source: Priming for welfare: gut microbiota is associated with equitation conditions and behavior in horse athletes | Scientific Reports

NOTES

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