Equine Development of Gut Microbiota

A young horse, called a foal. Photo credit: [1]

By Mira Allen

Topic: equine development of gut microbiota

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Introduction

In utero, horses intestinal tracts are close to sterile. Soon after birth, however, microbial colonization skyrockets. Proper colonization lasts about 50 days, and is incredibly important as improper microbial gut content can result in dysbiosis, causing inflammation and metabolic disease [1]. Equine hind-gut microbiota enable nutritional optimization from an otherwise nutrient-poor foraging diet via plant material fermentation [2]. The initial colonization, stabilization, and then weaning period (4-6 months old) as a foal transfers to solid food are important periods in establishing the microbial composition of the colon [1].

Most equine gut bacteria live in the colon, specifically in the caecum [2]. These bacteria degrade otherwise indigestible forage. The equine gut is composed of two main sections [2]:

Upper gut: stomach, jejunum, ileum (Increased microbiota variation and turnover as food is processed here first)
Lower stomach: caecum and colon (More stable microbiota. Most reside in the colon)

Because the microbiome processes food intake and is responsible for digestion, its disruption can cause inflammation and even result in metabolic disorders [2].

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Gut Colonization: Birth to Maturity

The stages of microbiome colonization in mammals are as follows:
- Initial colonization [1]
- Microbiota stabilization [1]
- Weaning (in foals: 4-6 months) [1]
- Transfer to solid foods (occurs gradually) [1]

While these are generally applicable in mammals, it has been demonstrated that the foal gut microbiome closely resembles their mother's around 60 days of age [1]. This means that their microbiome development occurs more rapidly than most other mammals. While it is unclear where colonization begins exactly, it is likely in utero, and if not, in the birth canal [1]. This is then furthered via the consumption of mare's milk and manure [1]. Manure consumption occurs most commonly until about 2 months of age [1].

Before 50 days old, gut microbiota composition is transient and dynamic. Research [1] has shown that change in similarity between individual foals and foals and adults occurs in these stages:
Day 7: large variation between individual foals
Day 20: more consistent between foals, but different from adults
Day 50: very similar to adult composition

These findings may differ between individuals depending on their housing (ie. stall or turnout), access to adult foods from birth (ie. grain, grass), and geographic location.

Species Composition

The core mature equine microbiome that has so far been documented to include:
- Bacteroides uniformis [1]
- Bacteroides fragilis [1]
- Parabacteroides [1]
- Butyricimonas (all Bacteroidetes)[1]
- Enterobacteriaceae (Proteobacteria) [1]
- Lactobacillus mucosae [1]
- Blautia producta [1]
- Streptococcus (all Firmicutes) [1]

References

Authored for BIOL 238 Microbiology, taught by Joan Slonczewski,at Kenyon College,2024