Original ResearchComparison of the Fecal Microbiota in Horses With Equine Metabolic Syndrome and Metabolically Normal Controls Fed a Similar All-Forage Diet
Introduction
Horse are hindgut fermenters and as such, their gut microbiota is predominantly populated by bacteria from the phyla Firmicutes [1], [2]. However, even in healthy horses, the gut microbiota is naturally highly diverse and highly variable. It is influenced by factors such as diet, age, and individual variation [1], [3], [4]. Disease states in particular can have a significant impact on the gut bacterial population in the animal. For example, there is evidence that a high-starch diet may increase the abundance of certain taxa from the family Veillonellaceae [5]. In addition, horses with chronic laminitis have differences in both microbiota abundance and diversity compared with controls [6], and the microbiota has significant changes in abundance during the onset of laminitis [7], [8].
Insulin resistance, general or regional adiposity, and a history of or predisposition to laminitis are the three main characteristics associated with equine metabolic syndrome (EMS) [9]. Equine metabolic syndrome is considered to be especially concerning to the equine population considering its connection to laminitis, which can result in inability for the animal to resume normal work or even euthanasia. Equine metabolic syndrome is comparable to metabolic syndrome (MetS) in humans, which is associated with similar factors, such as visceral obesity, glucose intolerance, and dyslipidemia [10], [11], [12].
In humans and mice, MetS and obesity have been linked to alterations in the intestinal microbiota [13]. It has been shown in high fat–fed mice that bacterial lipopolysaccharide (LPS) endotoxemia can induce inflammation and insulin resistance [14], both of which are considered to be influential in the pathophysiology of MetS [15]. Furthermore, age-related changes in the gut microbiota of mice have resulted in increased plasma LPS concentrations and a subsequent increase in markers of inflammation, indicating that shifts in the microbiota may play a major role in inducing low-grade systemic inflammation [16]. Studies in humans have shown that dietary changes can have a positive impact on the gut microbiota by reducing LPS-producing bacteria and are proposed as a possible therapeutic target for individuals with metabolic dysfunction [17], [18]. However, no data to date have been presented exploring possible differences in the gut microbiota of horses with EMS compared with metabolically normal controls, nor what impact these differences may have on the pathophysiology of the syndrome.
Investigation into the mechanisms and factors contributing to EMS is becoming increasingly important considering its negative health consequences in these horses, in particular, the increased risk of laminitis. Therefore, the objective of this study was to investigate and characterize the fecal microbiota of horses with naturally occurring EMS compared with metabolically normal non-EMS controls.
Section snippets
Horse Selection and Sample Collection
Twenty horses of mixed gender and breed were selected on the basis of EMS criteria as defined in the following section from the University of Kentucky's Department of Veterinary Science herd in the spring of 2014. Of these horses, 10 were classified as EMS, and 10 were classified as non-EMS controls. There was no significant difference in age between EMS and control horses (P = .903). All horses were housed at the University of Kentucky's Main Chance or Woodford farm facilities, maintained on a
Results
At the time of sampling, EMS horses were aged 13 ± 5 years (range 8–20 years), and non-EMS controls were aged 13 ± 3 years (range 10–19 years). Equine metabolic syndrome horses had greater values for fasting insulin, insulin 60 minutes after oral sugar administration, BCS, and CNS compared with controls (Table 2).
From the fecal samples analyzed for fecal microbiota differences, sequence processing and filtering yielded a total of 1,446,359 sequences (mean 72,318/sample, median 73,371.5,
Discussion
As expected, horses with a naturally occurring form of EMS had significantly greater measures of insulin resistance and obesity compared to a matched population of controls, considering these were the criteria used to establish the presence of EMS versus control. The fecal microbiota of horses with EMS also differed from those of the controls. Although differences in individual taxa were limited, there were changes in community structure, an overall measure of the components of the microbiota,
Conclusion
This preliminary study identified differences in the microbiota of horses with EMS compared with non-EMS control horses. Although the differences were limited, changes that were present could influence health and be associated with some of the clinical characteristics of EMS. Understanding the impact of microbiota alterations and factors that influence these changes may be important for optimizing management of this common syndrome in horses.
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