The equine gastrointestinal microbiome: Impacts of weight-loss

Obesity is an important equine welfare issue. Dietary restriction is the most effective weight-loss tool, although individual animals range in their weight-loss propensity. Gastrointestinal-derived bacteria play a fundamental role in host-health and have been associated with obesity and weight-loss in other species. This study evaluated the faecal microbiome (next-generation sequencing of 16S rRNA genes) of 15 obese Welsh Mountain pony mares, across 2 years (n = 8 Year 1; n = 7 Year 2) before and after a 7-week period of dietary restriction (1% body mass hay as daily dry matter intake). Losses in body mass ranged from 7.11% to 11.59%. Changes in the faecal microbiome composition following weight-loss included a reduction in the relative abundance of Firmicutes and Tenericutes and a reduction in indices of bacterial diversity. Pre-diet diversity was negatively associated with weight-loss. Pre-diet faecal acetate concentration was a strong predictor of subsequent weight-loss and negatively associated with Sphaerochaeta (Spirochaetes phyla) abundance. These data support a role for the faecal microbiome in weight-loss propensity in ponies and provide a baseline for research evaluating elements of the faecal microbiome in predicting weight-loss success in larger cohorts