The Equine Hindgut Microbiome

Researchers discuss the importance of diet on the microbial constituents of the large colon of the horse.
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A well-received presentation at the Equine Science Society symposium in June 2017 focused on the impact of diet on the equine hindgut microbiome.

The researcher said, "In horses fed a hay-based diet, the bacterial community shows a high richness and diversity, suggesting a strong resilience in the hindgut microbial ecosystems."

The researcher said, "In horses fed a hay-based diet, the bacterial community shows a high richness and diversity, suggesting a strong resilience in the hindgut microbial ecosystems."

Veronique Juilliand, PhD, DVM, of the Université Bourgogne-Franche-Comté/AgroSup in Dijon, France, described the importance of diet on the microbial constituents of the large colon of the horse. She stressed the importance of fibrous plant cell wall components that pass undigested in the upper intestinal tract. Colonic microorganisms break down these fibrous materials, then provide energy through the end products of their metabolism—in particular, short-chain fatty acids. Dysfunction of the hindgut can lead to obstructive or distention colic or to laminitis, to name a few common disease manifestations in the horse.

A common situation arises when there is an abrupt change in two different forage sources. Studies have found that if the two different hay sources are of close botanical and chemical composition, the hindgut microbiome of fibrolytic bacterial populations do not significantly change over either the short or long term. However, bacteria that are not involved in fiber digestion do experience changes within four hours of dietary modification.

The largest microbiota changes occur within 24 hours after there is an abrupt dietary change from a predominantly forage-based diet to one that includes grain concentrates (corn, oats or barley). Anaerobic bacterial concentrations in the hindgut increase and colonic pH decreases when high-starch diets are fed. Changes that last about seven days are particularly marked in the equine right ventral colon.

A recent study evaluated the effect of meal size and frequency of meal offerings on the microbiota in the horse’s cecum. Bacterial diversity did not differ between horses fed the full ration in one feeding compared to those receiving the same volume split over three feedings per day. However, the abundance of microorganisms did.

In conclusion, Juilliand noted: “In horses fed a hay-based diet, the bacterial community shows a high richness and diversity, suggesting a strong resilience in the hindgut microbial ecosystems.” Microbial populations in the hindgut are affected when horses are fed large meals of high-starch content, as often occurs in an equine athlete’s dietary management.

Author’s note: More details can be found in the Journal of Equine Veterinary Science, 52 (2017), pp. 23-28, in an article entitled “The Impact of Diet on the Hindgut Microbiome” by V. Juilliand and P. Grimm.