BY C. GISELLE COOKE; ZAMIRA GIBB; CHRISTOPHER G. GRUPEN;
JOANNA E. HARNETT
TABLE: THE AUTHORS
Prebiotics are non-digestible food ingredients that promote the growth of probiotic microorganisms in the intestines. They are marketed as feed supplements to support equine digestion, metabolism, growth, and immunity. Synbiotics are supplements that contain combinations of prebiotics and probiotic bacteria and/or yeasts. Both prebiotics and synbiotics are promoted for use in supporting equine digestion, enhancing athletic performance, reducing stress, and morbidity associated with intestinal disease.
1. Introduction
Equine veterinarians play an important role in advising on interventions that prevent and treat gastrointestinal disorders in horses. Equine gastrointestinal disorders include scouring in neonates [1], colitis and fatal colic events [2], parasitic gastrointestinal infections [3], gastric ulceration [4], salmonellosis associated inflammatory bowel disease [5], coronavirus infection with necrotizing enteritis and eosinophilic enterocolitis [5], sand-accumulation enteropathy [6] and caecal disorders [7]. Dysbiosis of the intestinal microbiome defined as “a loss of diversity, a bloom of potential pathobionts, and a loss of commensals” [8] may predispose horses to many of these gastrointestinal disorders [9].
Interestingly, there is evidence to suggest that equid type (size, breed, or conformation) may influence predisposition to the development of various gastrointestinal lesions; for example, larger breeds such as Clydesdales experience more caecal disorders, whereas smaller breeds and miniature horses are less likely to be affected by colon displacements [10]. Furthermore, extraintestinal conditions such as exacerbations in asthma [11], obesity [12], and impaired athletic performance [13] have all been associated with alterations to the composition and diversity of the equine gastrointestinal microbiome. Therefore, the equine microbiome has gained increasing attention in veterinary research [14] as reflected by the initiation of the Equine Gut Microbiome Project in 2015 [15].
Hindgut fermentation, which fundamentally influences intestinal microbiome composition [16,17], is a digestive process seen in animals with a simple, single-chambered stomach. These animals include equids, rhinoceros, koalas, rodents, and rabbits; in these mono-gastric herbivores, cellulose from plant foods is digested with the support of intestinal bacteria [18]. Popular interventions thought to alter the composition and diversity of the gastrointestinal microbiome include supplementation with probiotics and prebiotics. Probiotics are defined as “live microorganisms which, when administered in adequate amounts, confer a health benefit on the host” [19] and prebiotics are defined as “selectively fermented ingredients that result in specific changes in the composition and/or activity of the gastrointestinal microbiota, thus conferring benefit(s) upon host health” [20].
Prebiotics are widely used in equine management regimens to support the intestinal processing of a variety of feedstuffs, based on the belief that they improve the diversity and richness of the species that inhabit the intestinal microbiome [21]. Adding prebiotics containing fructo-oligosaccharides (FOS) or mannan-oligosaccharides (MOS) to high-fiber diets increases feed digestibility, supports energy production, and improves the general fitness and health of the horse [21]. Research conducted with Irish thoroughbreds undergoing a sudden change in feeding regimen found that digestive sensitivity particularly affected individuals carrying a limited abundance of hindgut core bacterial species [22]..
When probiotic bacteria and/or yeasts are combined with prebiotics, the formulation is referred to as a ‘synbiotic’. These combinations have been used in human studies to promote the growth of beneficial microbes, aiming to increase the diversity and richness of the intestinal milieu [23].
While there are limited studies in the equid, the potential role of pro- and prebiotics in human health and disease has been explored far more extensively, with the current PubMed citations exceeding five thousand. No summary of studies that report on the nutritional and therapeutic role of prebiotic and synbiotic supplementation in equine health and disease has been conducted to date. Therefore, the aim of this review was to provide an overview of the literature reporting on the use of prebiotic and synbiotic supplements, in equine nutritional practice. An online search of Embase and PubMed databases for papers published from inception to 2023, using the search terms ‘prebiotics’, ‘synbiotics’, ‘horses’, and ‘equine’, was conducted to identify original research evaluating the effects of prebiotics and synbiotics on the composition and/or metabolism of the equine intestinal microbiome, along with associated health outcomes.
