Pre, Pro, and Postbiotics: Supplementing the Gut Microbiome

Introduction

Many horse owners are familiar with the image of a feed room stuffed with boxes of supplements, custom supplement packs, and products. These products are the result of owners in search of solutions to hard keepers, exercise and travel stress, and ulcer prevention, just to name a few. These concerns have driven the massive growth of the equine supplement industry. In 2021, the equine supplement industry was valued at over $74 million dollars and is expected to continue rising at an almost 4% growth rate in coming years. Categories of supplements becoming more popular are prebiotics, probiotics, and postbiotics, in part due to benefits they may offer to a wide range of horses. These products supplement gut health linked to the gut microbiome and could simplify horse owners’ supplement shelves (Figure 1).

Horses are "hindgut fermenters," meaning about 60% of their daily energy comes from the activity of microorganisms residing in portions of the large intestine, specifically the cecum and colon. Bacteria, fungi, and protozoa are microorganisms in the gut responsible for this fermentation, and the population of these microorganisms is referred to as the gut microbiome. Microbiome health depends on the type and amount of "good" and "bad" bacteria. Prebiotics, probiotics, and postbiotics work in different ways to promote good bacteria and limit bad bacteria in the gut. The gut microbiome is very important to horses' overall health. Maintenance of the gut microbiome can help with digestion and nutrient absorption, healthy immune responses, and even bone health.

The Importance of the Equine Gut Microbiome

The gut microbiome can vary with diet, geographic location, exercise status, and age. Travel, exercise stress, dietary changes, the use of medications, or other changes to lifestyle can further affect the microbial populations in the gut. These changes can alter the balance of microbes and create what is known as gut dysbiosis. Gut dysbiosis is an imbalance of the "good" and "bad" bacteria in the gut. The gut microbiome is responsible for about 70% of the immune system, so harmful events like dysbiosis can be detrimental. Dysbiosis can result in conditions such as:

• Laminitis – gut microbiome changes trigger an immune response which leads to inflammation of the hoof laminae
• Ulcers – imbalance in the gut microbiome has been associated with gastric ulcers in horses
• Colic – the gas produced by microbial imbalance may increase horses’ risk of gas colic
• Behavioral Problems – the status of gut microbes have an impact on mood, anxiety, and behavior

It is clear the gut microbiome has impacts throughout the body, affecting horses in a variety of ways (Figure 2). This makes the use of prebiotics, probiotics, and postbiotics a promising addition to many horses' diets.

Prebiotics

What are Prebiotics?

Prebiotics are a class of dietary supplements consisting of carbohydrates, short-chain fatty acids, and other dietary components that provide fuel for good gut microbes to help them survive and grow. Supporting good gut microbes promotes healthy digestion and the production of beneficial microbe byproducts. Prebiotics can be found in commercial supplements as well as naturally in beet pulp, oats, and soy hulls (Figure 3).

Benefits of Prebiotics

Prebiotics promote the health of good gut microbes by providing dietary support for the microorganisms. Benefits of this support may include:

• Tolerance to high concentrate diets
• Improved overall digestion
• Increased insulin sensitivity in insulin-resistant horses
• Improved feed digestibility and nutrient absorption

Supplementing with Prebiotics

Prebiotics have demonstrated a number of potential benefits to horses. However, there are some important considerations when supplementing horses with prebiotics. While prebiotics are intended to pass into the hindgut undigested, some studies have found digestion begins in the foregut, prior to reaching the microorganisms they are intended to impact. The digestion of plant sugars that are components of some prebiotic supplements in the foregut could increase acid production and therefore increase the risk of gastric ulcers. Because of this, prebiotics should be used with care and the instruction of a veterinarian.

Probiotics

What are Probiotics?

Probiotics are live bacteria or yeast that increase populations of good bacteria. While prebiotics provide fuel to microbes already in the gut, probiotics directly add more beneficial colonies. 

Benefits of Probiotics

Probiotics can benefit digestion, nutrient absorption, gut lining strength and health, bone health, and even behavior. Because probiotics add colonies of microbes to the gut, the strain and dose are important as they may have different impacts. When reading a feed tag, some common probiotic strains you may see include:

• Lactobacillus – strains of lactobacillus (e.g., L. rhamnosus, L. fermentum, and L. casei) can benefit horses by inhibiting growth of harmful bacteria, improving digestion of high-starch feeds, reducing risk factors of hindgut acidosis, strengthening the immune system, and reducing fatigue in exercising horses.
• Bifidobacterium – strains of Bifidobacterium may benefit horses by increasing the production of energizing B vitamins, inhibiting harmful gut microbes, and reducing intestinal pH, which improves vitamin, electrolyte, and mineral absorption.
• Saccharomyces – most yeast-type probiotics used in the United States are strains of saccharomyces (e.g., S. cerevisiae and S. boulardii). Saccharomyces strains can strengthen immune responses, aid in management and prevention of gastric ulcers, disable hindgut toxins, and maintain the strength and health of the intestinal lining, which can work to prevent leaky gut syndrome.

Supplementing with Probiotics

Many ration balancers contain probiotic yeasts to promote healthy digestion. Research is still ongoing to determine the most beneficial strains and doses of probiotics for horses. There is some risk associated with probiotic supplementation, though, as it involves the introduction of new bacteria into horses’ digestive tracts. This presents a risk of introducing microbes with antibiotic-resistant genes. Because of this, it is recommended probiotics be supplemented while working with your veterinarian or equine nutritionist.

Postbiotics

What are Postbiotics?

While prebiotics fuel existing microbes and probiotics supply the gut with new good microbes, postbiotics are the resulting byproducts of gut microbe activity. Postbiotics, like prebiotics, are non-living and consist of vitamins, short-chain fatty acids, and enzymes. Postbiotics have recently become a hot topic in nutrition and research because they do not risk the introduction of live colonies of bacteria into the microbiome. Instead of going through the process of supporting or introducing new beneficial microbes, postbiotics focus on providing the end products that present health advantages, such as amino acids and B vitamins.

Benefits of Postbiotics

Research surrounding postbiotic supplementation is new and relatively limited. However, postbiotic supplementation research has already demonstrated some benefits in horses. For example, studies have found postbiotic supplementation maintained a healthy gut microbiome under stressful conditions, reduced markers of inflammation during exercise, and strengthened horses' response to influenza vaccinations. Postbiotics may also hinder the growth of bad bacteria and have anti-inflammatory effects. Research on postbiotics is relatively new and rapidly expanding, and initial studies appear promising.

Supplementing with Postbiotics

While postbiotics are relatively novel, there are several commercial postbiotic products and supplements emerging. Often, commercial products provide postbiotics in conjunction with prebiotics or probiotics to derive benefits from both classes of supplements.

Synbiotics

Supplementation of prebiotics, probiotics, and postbiotics is often done in combination, referred to as “synbiotics.” Traditionally, this term has referred to the use of prebiotics and probiotics together to introduce good microbes while simultaneously fueling them (Figure 4). This is an emerging area of research, but some studies conducted in chickens revealed an advantage of symbiotic use compared to the use of one class of prebiotics, probiotics, or postbiotics alone. With the growth of postbiotics within the industry, some products are beginning to introduce postbiotics in synbiotic supplementation as well.

Which Horses Need These Supplements?

Many of the potential benefits of prebiotics, probiotics, and postbiotics surround inflammation, immune system strength, digestibility, and nutrient absorption, and as such, there are many classes of horses that could stand to benefit from supplementation:

• Horses medicated with antibiotics or nonsteroidal anti-inflammatory drugs
• Horses experiencing stressors such as dietary changes, travel, or increased training
• Horses with high-starch diets
• Horses suffering from leaky gut syndrome
• Senior horses
• Hard keepers

Conclusions

The health of the equine gut microbiome has important impacts to horses' health. Ensuring the health of the gut microbe may improve digestion, prevent ulcers, and aid in the management of conditions such as leaky gut. This could help horses remain healthy through stressful periods of training, travel, or lifestyle changes. Prebiotics, probiotics, and postbiotics all have proven benefits in promoting the health of the gut microbiome. As such, supplementation may stand to benefit a wide range of horses and offer important benefits. As a reminder, supplementation of these classes of supplements should be done with the help of a veterinarian and/or an equine nutritionist.

Resources

Schoster, A., J.S. Weese, L. Guardabassi (2014). Probiotic use in horses - what is the evidence for their clinical efficacy? Journal of Veterinary Internal Medicine 28:6. doi.org/10.1111/jvim.12451.