Correlation of hindgut microbiome and fermentation properties with a history of gas and/or impaction colic in Japanese draft horses

Colic, a major gastrointestinal disease in horses, has a high recurrence rate and can lead to surgery or fatal outcomes, highlighting the need for effective prevention measures. Disruption of the microbiome is a multifaceted problem and can occur from a variety of factors, such as high-concentrate diets, which can then potentially cause colic. However, individual variation in the incidence of colic can occur when under identical management practices. The aim of this study was to characterize the fecal bacterial composition of Japanese draft horses with and without a history of colic in the past two years under identical feeding conditions to determine if specific bacterial taxa are associated with either phenotype. A fecal bacterial community analysis was performed via sequencing of the V3-V4 region of the 16S rRNA gene. The fecal lactate concentration was measured using high-performance liquid chromatography. Our results show a significant decrease in microbial evenness in horses with a history of colic along with an increase in <i>Streptococcus</i>. The fecal lactate concentration was higher in the colic group compared with the non-colic group, which may be attributed to the higher abundance of <i>Streptococcus</i>. Horses without a history of colic were characterized by amplicon sequence variants belonging to bacteria associated with fiber degradation, including Rikenellaceae RC9, Kiritimatiellae, and Clostridium. Overall, our results align with previous studies on equine colic epidemiology and suggest that the bacterial microbiome composition, independent of diet, may be related to the recurrence of colic.