Changes in the Total Fecal Bacterial Population in Individual Horses Maintained on a Restricted Diet Over 6 Weeks.

Kirsty Dougal,Patricia A Harris,Caroline M Argo,Susan E Girdwood,Gemma C Curtis,Christopher J Creevey,Clare F Barfoot,Charles J Newbold

doi:10.3389/fmicb.2017.01502

Abstract

Twelve mature (aged 5–16 years) horses and ponies of mixed breed and type were fed restricted (1.25% BM Dry matter) quantities of one of two fiber based diets formulated to be iso-caloric. Diet 1 comprised of 0.8% body mass (BM) of chaff based complete feed plus 0.45% BM low energy grass hay (the same hay used for both diets). Diet 2 comprised 0.1% BM of a nutrient balancer plus 1.15% BM grass hay. Fecal samples were collected at week 10 and week 16. DNA was extracted and the V1-V2 regions of 16SrDNA were 454-pyrosequenced to investigate the bacterial microbiome of the horse. The two most abundant phyla found in both diets and sampling periods were the Firmicutes and Bacteroidetes. There was a clear reduction in Bacteroidetes with a concordant increase in Firmicutes over time. There was a limited degree of stability within the bacterial community of the hindgut of horses, with 65% of bacteria retained, over a 6 week period whilst on a uniform diet. The presence of a core community defined by being present in all samples (each animal/diet combination) included in the study and being present at 0.1% relative abundance (or greater) was identified. In total 65 operational taxonomic units (OTUs) were identified that fit the definition of core making up 21–28% of the total sequences recovered. As with total population the most abundant phyla were the Bacteroidetes followed by the Firmicutes, however there was no obvious shift in phyla due to period. Indeed, when the relative abundance of OTUs was examined across diets and periods there was no significant effect of diet or period alone or in combination on the relative abundance of the core OTUs.

Highlights

Investigations into the bacterial community in the large intestine of the horse have far mainly involved samples from single time points
We suggest that if the core bacterial community, shared in all animals at all times, remains relatively stable in terms of relative abundance over time, this may be indicative of a stable community which may have a degree of resilience to normal changes in the animals’ environment and management
The horses and ponies were randomly assigned to two groups; each fed a different diet at 1.25% as dry matter (DM) of actual body mass (BM)

Summary

Introduction

Investigations into the bacterial community in the large intestine of the horse have far mainly involved samples from single time points. Blackmore et al (2013) found the bacterial community to be significantly different in structure after 10 weeks on a uniform fiber based diet. To our Temporal Stability of Equine Microbiome knowledge only two studies have investigated the temporal stability of the bacterial community in the equine hindgut whilst on a uniform diet, using culture independent methods (Willing et al, 2009; Blackmore et al, 2013). These two studies confirmed the findings, from single time point data, that there is large inter-animal variability (Costa et al, 2012; Steelman et al, 2012)

Methods

Results

Discussion

Conclusion