The equine gastrointestinal microbiome: impacts of weight-loss

Abstract

Background: Obesity is an important equine welfare issue. Whilst dietary restriction is the most effective weight-loss tool, 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, in the same 11-week period across 2 years (n = 8 Year 1; n = 7 Year 2). Following a 4-week acclimation period (pre-diet phase) during which time individuals were fed the same hay to maintenance (2% body mass (BM) as daily dry matter (DM) intake), animals underwent a 7-week period of dietary restriction (1% BM hay as daily DM intake). Faeces were sampled on the final 3 days of the pre-diet phase and the final 3 days of the dietary restriction phase. Bacterial communities were determined using Next Generation Sequencing of amplified V1-V2 hypervariable regions of bacterial 16S rRNA.

Results: 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 phylum) abundance. When animals were divided into 3 groups (high, mid, low) based overall weight loss, pre-diet bacterial community structure was found to have the greatest divergence between the high and low weight-loss groups (R = 0.67, p < 0.01), following PERMANOVA and ANOSIM analysis.

Conclusions: Weight-loss in this group of ponies was associated with lower pre-diet faecal bacterial diversity and greater pre-diet acetate concentration. Overall, 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.

Keywords: Apparent digestibility; Biomarkers; Equine, equine obesity; Faecal microbiome; Insulin dysregulation; Volatile fatty acid; Weight-loss.

Fig. 1

Changes in body mass over the 7-week dietary restriction phase of the study. (A) Marginal mean plot derived predicted body mass change (n = 15). Shaded area corresponds to 95% confidence intervals. (B) Predicted cumulative proportional weight-loss for individual animals (adjusted to Week 0; n = 15)

Fig. 2

Marginal mean plots illustrating associations between overall predicted proportional weight-loss and pre-diet diversity indices: (A) Species observed, (B) Shannon-Weiner, (C) Inverse Simpson. Shaded area corresponds to 95% CI. n = 15

Fig. 3

Marginal mean plots illustrating pre-diet VFA concentrations: (A) Acetate, (B) Propionate, (C) Butyrate, (D) Branched chained volatile fatty acids (BCVFA). Shaded area corresponds to 95% CI. n = 15

Fig. 4

Stacked histogram illustrating the relative abundance of the dominant bacterial phyla (present at > 0.05% relative abundance) before (pre-diet), and after 7 weeks of dietary restriction (post-diet; n = 15)

Fig. 5

Stacked histogram illustrating the relative abundance of the dominant bacterial genera (present at > 0.05% relative abundance) before (pre-diet), and after 7 weeks of dietary restriction (post-diet; n = 15)

Fig. 6

(A) Principal Co-ordinate analysis plot of the pre-diet bacterial community from the three weight-loss groupings using Bray-Curtis similarity index. (B) Distance-based redundancy analysis illustrating associations between the pre-diet bacterial community structure and faecal volatile fatty acid concentrations (mM) and pH