How early gut development can shape a foal’s future
The foundations of future equine health may begin developing far earlier than we once thought.
Increasingly, research from both human and animal studies suggest that microbiome development in early life plays an important role in shaping immunity, resilience to stress, behaviour, disease susceptibility and athletic performance.
The microbes within a horse’s hindgut are essential for digestion, nutrient utilisation, immune development and maintaining overall health – with additional influence on stress responses, behaviour and long-term resilience via the gut-brain axis.
The microbiome begins developing immediately after birth, as foals are exposed to microbes from the mare, her birth canal, milk, the wider environment and behaviours like coprophagia (eating manure). The microbial communities that develop during this period support the maturation and development of the immune system.
However, the microbiome is also highly sensitive in this stage of life. Factors such as stress, infection, antibiotic exposure, lack of breastfeeding, environmental conditions and dam genetics may all significantly influence how these microbes establish and mature.
A critical window
Researchers now believe there may be a “critical window” early in life during which the microbiome helps shape longer-term health outcomes in both animals and humans.
A landmark 2024 study by Professor Chris Proudman and colleagues at the University of Surrey followed 52 Thoroughbred foals from birth to three years of age.
Over the course of the study, researchers collected hundreds of faecal samples alongside veterinary health records and racing performance data to better understand how the developing gut microbiome impacted future health and athletic performance.
One of the study’s most significant findings was the identification of a potential “critical window” at approximately 28 days of age.
Foals with greater bacterial diversity during this period demonstrated improved health outcomes later in life, including lower risk of respiratory disease, as well as stronger racing performance. In contrast, foals exposed to antibiotics in their first month showed significantly reduced microbial diversity, were more likely to develop respiratory disease and performed worse in their racing careers.
The researchers also identified correlations between specific bacterial populations and athletic success, opening a door to exciting future research.
While this research does not prove direct cause and effect, it certainly highlights the important role of the early-life microbiome in foals.
Why 28 days?
Researchers are still working to understand exactly why this period appears to be so important. However, several important environmental and physiological changes occur at around 1 month of age.
At this point in their lives, foals are becoming increasingly exposed to pasture, grass, soil microbes and maternal feed while still suckling. At the same time, the passive immunity they obtained from colostrum is declining.
After they are born, foals rely heavily on antibodies like immunoglobulin G (IgG) absorbed through colostrum, but by 28 days of age, these maternally-derived antibodies have reduced by more than 50%. Meanwhile, the foal’s own immune system is still maturing until they are around 90 days old.
The rapid and overlapping development of the neonatal immune system and gut microbes may help explain the importance of the microbiome during this “critical window”.
More than just digestion
Wider evidence demonstrates close links between the gut microbiome, immune function, metabolism and the nervous system. The gut and brain communicate constantly through the gut-brain axis, with microbial metabolites capable of influencing stress responses, behaviour and neurological function.
Researchers also believe that differences in stress responsiveness and resilience between individual horses may be influenced, in part, by early-life microbial development. During the neonatal period, the immune system, nervous system and gut microbiome develop closely alongside one another, and growing evidence suggests these interactions may help shape how horses respond to stress later in life.
Supporting the developing microbiome
Although many questions remain unanswered, the growing body of evidence reinforces the importance of supporting healthy microbial development during a foal’s early life.
The findings of Prof Proudman and his team particularly highlight the importance of proper nutrition, careful use of antibiotics, strong maternal health and minimising unnecessary stress during this “critical window”.
Management practices that support microbial development may help provide a strong foundation for the foal’s long-term health and resilience:
- Ensure sufficient colostrum intake immediately after birth
- Provide mares with fibre-rich diets and access to high quality grazing and/or forage
- Administer targeted antibiotics only when necessary and under strict veterinary supervision
- Consistent feeding and activity routines
- Minimise sudden environmental or social changes
- Providing appropriate turnout, forage access and social interaction
- Gradual transitions during weaning and management changes
- Maintain hygienic, but not overly sterile, environment
As our understanding of the equine microbiome continues to evolve, it is increasingly clear that the first few weeks of life may shape far more than we once realised.
Supporting hindgut stability during this “critical window” may provide foals with the best possible foundation for future health, resilience and performance.