Effect of age and the individual on the gastrointestinal bacteriome of ponies fed a high-starch diet.

Philippa K Morrison,Hilary J Worgan,Dai H Grove-White,Patricia A Harris,Clare Barfoot,Caroline Mcg Argo,Alexandra H Dugdale,Charles J Newbold,Eleanor Jones,Nicoletta Righini

doi:10.1371/journal.pone.0232689

Abstract

Bacteria residing in the gastrointestinal tract of mammals are crucial for the digestion of dietary nutrients. Bacterial community composition is modified by age and diet in other species. Although horses are adapted to consuming fibre-based diets, high-energy, often high-starch containing feeds are increasingly used. The current study assessed the impact of age on the faecal bacteriome of ponies transitioning from a hay-based diet to a high-starch diet. Over two years, 23 Welsh Section A pony mares were evaluated (Controls, 5–15 years, n = 6/year, 12 in total; Aged, ≥19 years, n = 6 Year 1; n = 5 Year 2, 11 in total). Across the same 30-week (May to November) period in each year, animals were randomly assigned to a 5-week period of study and were individually fed the same hay to maintenance (2% body mass as daily dry matter intake) for 4-weeks. During the final week, 2g starch per kg body mass (micronized steam-flaked barley) was incorporated into the diet (3-day transition and 5 days at maximum). Faecal samples were collected for 11 days (final 3 days hay and 8 days hay + barley feeding). Bacterial communities were determined using Ion Torrent Sequencing of amplified V1–V2 hypervariable regions of 16S rRNA. Age had a minimal effect on the bacteriome response to diet. The dietary transition increased Candidatus Saccharibacteria and Firmicutes phyla abundance and reduced Fibrobactres abundance. At the genera level, Streptococcus abundance was increased but not consistently across individual animals. Bacterial diversity was reduced during dietary transition in Streptococcus ‘responders’. Faecal pH and VFA concentrations were modified by diet but considerable inter-individual variation was present. The current study describes compositional changes in the faecal bacteriome associated with the transition from a fibre-based to a high-starch diet in ponies and emphasises the individual nature of dietary responses, which may reflect functional differences in the bacterial populations present in the hindgut.

Highlights

For all mammals, the symbiotic relationship that exists between the host and the vast community of microorganisms inhabiting the gastrointestinal tract is vital in maintaining whole-body homeostasis, through the provision and digestion of dietary nutrients
It has previously been shown that aged horses display a reduction in species richness and bacterial diversity when fed a range of different diets [9] and it was hypothesised that aged ponies in the current study would demonstrate a reduction in bacterial diversity, and a more marked
The current study has described changes in the faecal bacteriome composition of ponies associated with the transition from a hay-based to a high starch diet

Summary

Introduction

The symbiotic relationship that exists between the host and the vast community of microorganisms inhabiting the gastrointestinal tract is vital in maintaining whole-body homeostasis, through the provision and digestion of dietary nutrients. The fermentation of dietary starch in the hindgut of horses by resident bacterial populations has been shown to lead to increases in the abundance of amylolytic bacteria including Lactobacilli and Streptococcus and reductions in cellulolytic bacterial populations [8,10]. These changes in the bacterial populations are associated with a reduction in gastrointestinal pH due to increases in lactate production, and may lead to the development of conditions such as colic and laminitis in susceptible animals. The microbial response to starch feeding is not consistent between animals, with the extent of the microbial response appearing to vary between individual animals [11]

Methods

Results

Discussion

Conclusion