Effect of Sugar Beet Pulp on the Composition and Predicted Function of Equine Fecal Microbiota

SIMPLE SUMMARY: As hindgut fermenters, horses are reliant on the complex microbial communities residing in the digestive tract. The composition of the fecal microbiome is shaped by dietary factors among others, and common but potentially fatal gastrointestinal conditions, such as colic and colitis, are associated with changes in the fecal microbiome. In relation to health, certain bacteria in an equine hindgut utilize dietary fiber to produce short-chain fatty acids, and sugar beet pulp is a high-fiber feed supplement believed to act as a prebiotic and promote good equine gut health. The information regarding the influence of sugar beet pulp and other prebiotics on the fecal microbiome of horses is limited. Evidence of the effect of sugar beet pulp on the fecal microbiome might support its use as a routine preventive measure against colic and colitis. ABSTRACT: The purpose of this study is to determine the effect of the partial replacement of dietary hay with sugar beet pulp (SBP) on the composition and predicted function of the fecal microbiota of healthy adult horses. Fecal samples were collected daily for 12 days from six adult horses after removal from pasture, including a five-day acclimation period, and a seven-day period following the introduction of SBP into their diet, and compared to six untreated horses over a comparable period. Fecal DNA was subjected to 16S rRNA amplicon sequencing and a longitudinal analysis was performed comparing the composition and predicted function. While no significant treatment-associated changes in the richness, alpha diversity, or beta diversity were detected, random forest regression identified several high-importance taxonomic features associated with change over time in horses receiving SBP. A similar analysis of the predicted functional pathways identified several high-importance pathways, including those involved in the production of L-methionine and butyrate. These data suggest that feeding SBP to healthy adult horses acutely increases the relative abundance of several Gram-positive taxa, including Cellulosilyticum sp., Moryella sp., and Weissella sp., and mitigates the predicted functional changes associated with removal from pasture. Large-scale studies are needed to assess the protective effect of SBP on the incidence of the gastrointestinal conditions of horses.