Comparative Development of the Intestinal Microbiota in Domesticated and Semi‑Feral Foals: Implications for Digestive Health and Breeding Practices

Abstract

The equine intestinal microbiota plays a central role in digestive, immune and metabolic health. A study published in 2020 in Animal Microbiome (Tavenner, McDonnell & Biddle) compared the maturation of the microbiota in semi‑feral foals with that of foals raised under conventional domestic conditions, including early access to concentrate feeds. The results reveal significant divergences within the first weeks of life, suggesting that some common breeding practices may be misaligned with the biological needs of the young horse.

1. Introduction

The equine intestinal microbiota is a complex community of microorganisms involved in fiber digestion, vitamin synthesis, immune modulation and certain behavioral functions. Dysbiosis of this ecosystem has been associated with colic, diarrhea, gastric ulcers and laminitis. Current evidence indicates that the microbial community of the foal stabilizes between one and two months of age, and that the method of weaning does not induce major changes when properly managed.

2. Natural Development of the Foal Microbiota

In natural conditions, microbial colonization is influenced by maternal contact, continuous access to grass, group living and the absence of starch‑rich concentrate feeds. Fibrolytic bacteria, essential for the degradation of plant fibers, form the functional core of the herbivorous equine microbiota. Their early establishment determines the foal’s future ability to efficiently utilize forage.

3. Comparison Between Semi‑Feral and Domestically Raised Foals

3.1. Semi‑Feral Foals

In the study by Tavenner et al., Shetland foals raised in semi‑feral conditions developed a significantly more diverse microbiota than domestically raised foals. This increased diversity is associated with greater digestive resilience, improved stability during dietary changes and enhanced resistance to stress. Dominant taxa included fibrolytic bacteria adapted to the degradation of complex plant fibers.

3.2. Domestically Raised Foals

Domestic foals were kept in stalls during the first week of life, then moved to small enclosures with access to their dam’s concentrate feed. By the second to third week, these foals exhibited a notable accumulation of lactic acid–producing bacteria (Lactobacillaceae). These bacteria proliferate in the presence of starch in the hindgut, produce lactic acid, lower intestinal pH and inhibit fibrolytic bacteria. This pattern results from the foal’s natural tendency to imitate the dam’s feeding behavior and consume her ration.

4. Long‑Term Consequences

Although the microbiota remains modifiable, the early weeks of life represent a critical programming period. Early exposure to starch can durably orient the microbial community toward a profile less suited to fiber digestion. This may help explain certain adult sensitivities, such as poor forage utilization, increased susceptibility to laminitis or a predisposition to gastric ulcers. These findings suggest that some digestive issues attributed to genetics may instead stem from early‑life management practices.

5. Practical Implications for Breeding

Current evidence supports raising foals on pasture, in social groups, with exclusive access to maternal milk and grass during the first weeks. Early introduction of starch‑rich concentrate feeds should be avoided. When supplementation becomes necessary after weaning, protein‑rich, low‑starch balancers are preferable. High‑quality hay should be considered a primary feed, not a filler. Botanical diversity and environmental quality strongly influence microbial diversity and represent major assets for healthy development. It is also important to note that research on the equine microbiome is recent, and many historical studies were conducted on supplemented foals, potentially biasing our understanding of their true digestive capacities.

6. Conclusion

The findings of Tavenner et al. demonstrate that foals raised in natural conditions develop a more diverse and functional microbiota than those exposed early to concentrate feeds. The authors suggest that the management of semi‑feral horses may serve as a reference for defining a healthy intestinal microbiota in domestic horses. These results encourage a re‑evaluation of certain intensive breeding practices, emphasizing that the biology of the foal has not evolved at the same pace as modern management systems.

Reference

Tavenner MK, McDonnell SM, Biddle AS. Development of the equine hindgut microbiome in semi-feral and domestically managed foals. Animal Microbiome. 2020;2:43. doi:10.1186/s42523-020-00060-6