A Standard Scale to Measure Equine Keeper Status and the Effect of Metabolic Tendency on Gut Microbiome Structure.

Alexa C B Johnson,Amy S Biddle

doi:10.3390/ani11071975

Abstract

Simple SummaryHorses with different metabolic tendencies are anecdotally referred to as “easy” or “hard” keepers. Easy keepers tend to gain weight easily while hard keepers require extra feed to maintain condition. Both easy and hard keeper horses carry a managerial and financial burden which can be a dissuading factor for horse shoppers. This research uses energy intake/need and body condition to develop a standard Equine Keeper Status Scale (EKSS) for assigning keeper status. The microbiome compositions based on EKSS assignments are then compared to explore microbiome differences based on metabolic tendencies of each group. The EKSS can be used by owners to accurately assess their horses’ metabolic tendencies and make improved feeding decisions to meet their horses’ needs. Understanding microbiome differences between easy, medium and hard keeper horses points to potential microbial roles in these metabolic tendencies.Thriftiness in horses has been associated with more efficient nutrient harvesting in digestion, absorption and/or utilization, but the relative contribution of the gut microbiome to host metabolic tendency is not well understood. Recognizing the unreliability of owner reported assignment of keeper status, this research describes a novel tool for calculating whether a horse is an easy (EK) or hard (HK) keeper and then characterizes microbiome differences in these groups. The Equine Keeper Status Scale (EKSS) was developed and validated based on data gathered from 240 horses. Estimates of dietary energy intakes and requirements to achieve the optimal BCS score of 5 were used in EKSS assignments. Sixty percent of owners’ characterizations disagreed with EKSS identified keeper assignments. Equine fecal 16S rRNA profiles (n = 73) revealed differences in α and β diversities and taxa abundances based on EKSS assignments. EK communities had more Planctomycetes and fewer Euryarcheaota, Spirochaetes and Proteobacteria than HK indicating functional differences in nutrient harvesting between groups. Differences in the gut microbiomes of horses based on keeper assignment point to host/microbial interactions that may underlie some differences in metabolic tendency. The EKSS enables robust, repeatable determination of keeper status which can be used by researchers and horse owners.

Highlights

The definition of the equine keeper status is ambiguous and poorly characterized within the equine community
With no comparable reported population rates of medium keepers” (MK) and hard keepers” (HK) found in the literature, we report the first population rates for these animals with Equine Keeper Status Scale (EKSS) assignments (25% MK and 40% HK)
Distinctions found in the observational study of the gut microbiome structure based on EKSS assignments suggest differences in microbial diversities and phylogenetic community relatedness within and between keeper statuses

Summary

Introduction

The definition of the equine keeper status is ambiguous and poorly characterized within the equine community. The current ideology behind the keeper status is the combination of equine body condition and how readily the animal maintains weight to determine how the horse should be fed [1]. Animal owners use body condition as a key indicator of horse health and consider weight loss being a greater cause for concern (than weight gain) as it reflects more poorly on the quality of care [5]. Owners may make inappropriate feed choices based on perceived negative connotations of owning an overweight/obese or underweight horse [6] or social pressure to provide their animal with treats and grain-based meals [7,8] regardless of the horse’s needs

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