The postbiotic supplement—derived from the probiotic yeast—appears to maintain horses’ gut microbiota stability even after mild stress that would typically upset the microscopic communities lining the intestines. Therefore, the supplement might encourage not only good digestive health but also proper immune function, said Sharon A. Norton, BS, MS, PhD, principal research lead of the Companion Animal Microbiome R&D Team at Cargill Animal Nutrition in Minneapolis, Minnesota.

“Horses have to cope with stress in many forms on a daily basis,” she said. “Both diet- and exercise-induced stress have been associated with microbiome changes in horses. Unstable microbiomes represent a ‘crack in the armor’ of the natural defenses of the horse and can allow opportunistic pathogens to gain a foothold and negatively affect the horse’s health.”

Her team’s recent results suggest that supplementing horses might be particularly useful in competition horses, noted Norton.

“In practice, if someone is transporting their horse to an event, in order for that horse to be healthy and to perform well, it needs to be able to optimally assimilate and digest the nutrients from the feedstuffs,” she said. “And the gut microbiome plays a big role in that. What our study revealed is that the postbiotic helped the gut microbes ‘weather the storm’ better than those in horses that did not receive the postbiotic.”

The Postbiotic: A Supplement that Promotes Gut Stability

Prebiotics are supplements that feed probiotics—the healthy living organisms such as yeast that improve the gut microbiota. Probiotics produce vitamins, amino acids, and other metabolites that promote good nutritional health and energy, Norton said.

The researchers realized they could also supply horses with those metabolites directly to complement those being produced in the gut, she said. So, they collected metabolites from lab-grown Saccharomyces cerevisiae yeast and created the yeast postbiotic supplement.

“Because the mode of action of postbiotics does not rely on presence of live organisms in the final product, they represent an attractive alternative for horse feed and direct supplementation because they are highly stable and retain efficacy through typical feed and supplement manufacturing processes,” Norton said.

Testing Gut Microbiome Stability Before and After Tethering Stress

The research team studied 20 2-year-old Quarter Horses in light training four days a week. All the horses were fed daily rations with 60% of the nutritional content coming from Coastal bermudagrass hay and the other 40% from concentrated feeds.

Half the horses also received 21 grams of the commercially prepared Saccharomyces cerevisiae fermentation product (SCFP), sprinkled onto their feed every day for 60 days, she said. The team collected fecal samples from each horse at the start of the study and on Days 28 and 56.

On Day 57, the researchers induced mild airway inflammation using a scientifically and ethically approved technique of tying the horses’ heads slightly higher than their withers temporarily. The horses could still eat and drink during this time, she added.

“This model was excellent in that it mimicked a common habit and practice horse owners employ when transporting their horses,” Norton explained. “And it highlights the point of how even the most innocuous of day-to-day events a horse encounters can be profoundly stressful.”

The team collected fecal samples just before tying up the horses, as well as 12, 24, and 72 hours later, she said.

The Goal: A More Stable Horse Microbiome During Stress

DNA sequencing of the horses’ feces revealed that the postbiotic had little effect, if any, on the horses’ microbial profile over the first 56 days of the study as they followed their regular, relatively nonstressful daily routines, according to Norton.

However, the effects of the supplement became clear once the horses experienced the head-tying stress, she explained.

That stress was associated with a significant drop in microbiome quality in both groups—as evidenced by reduced species richness, said Norton. But the horses consuming the postbiotic fared better.

“Overall, horses supplemented with SCFP exhibited robust microbial diversity after stress, with less variation and an overall lower stress-induced drop in diversity when compared to the control group,” the researchers reported.

Specifically, the SCFP-treated horses had more stable microbiomes at each of the tested time points, whereas untreated horses had greater fluctuation in diversity.

The findings suggest that supplementation with the yeast-derived postbiotic could help horses’ gut microbiomes cope with stress better—which could lead to better health and welfare.

The supplements might have particular benefits for competition horses because they face a wide range of stressors on a regular basis, she added.

“Even something as innocuous as tethering horses and restricting the movement of their heads—which is common when transporting horses safely back and forth from events—can trigger local and systemic inflammatory responses,” Norton explained.

The study, “Saccharomyces cerevisiae fermentation product improves robustness of equine gut microbiome upon stress” appeared in Frontiers in Veterinary Science in February 2023.