Effects of increasing levels of purified beta-1,3/1,6-glucans on the fecal microbiome, digestibility, and immunity variables of healthy adult dogs

Marchi, P. H., Vendramini, T. H. A., Zafalon, R. V. A., Príncipe, L. d. A., Cesar, C. G. L., Perini, M. P., Putarov, T. C., Gomes, C. O. M. S., Balieiro, J. C. d. C., & Brunetto, M. A. (2024). Effects of increasing levels of purified beta-1,3/1,6-glucans on the fecal microbiome, digestibility, and immunity variables of healthy adult dogs. Microorganisms, 12(1), 113. https://doi.org/10.3390/microorganisms12010113

Yeast Beta-Glucans And Dogs: What This 2024 Study Shows

The University of São Paulo team evaluated graded levels of a purified yeast beta-1,3/1,6-glucan in otherwise similar dry dog foods to see how dose influences digestibility, the fecal microbiome, and select immune measures in healthy dogs. The paper positions beta-glucans as bioactive fibers that occur in algae, bacteria, cereals, fungi (including mushrooms), and yeasts; this trial focuses specifically on the yeast form.

How The Researchers Set The Stage

In the introduction, the authors explain that diet strongly shapes the canine gut microbiome and that prebiotics can steer bacterial communities. They note beta-glucans are structurally diverse polysaccharides found across multiple natural sources, with prior work in dogs suggesting effects on glucose control, lipid metabolism, and immune function. This context is presented to justify testing dose-response effects of a purified yeast beta-glucan in a controlled feeding study.

What The Study Tested

• Ingredient: The supplement was a purified beta-1,3/1,6-glucan extracted from the cell walls of Saccharomyces cerevisiae (brewer’s yeast). The product was 60% active beta-glucan, and it was blended into the test diets before extrusion.
• Design: The researchers used what’s called a “Latin square” design—a way of rotating diets so that every dog tries every diet, but at different times. This balances out individual differences (like if one dog naturally digests protein a little better than another) because each dog acts as its own control. In this case, they used two 4×4 Latin squares:
  • 8 healthy adult dogs were divided into two groups of 4.
  • Each group cycled through the four test diets (0.00%, 0.07%, 0.14%, and 0.28% beta-glucan) in different sequences.
  • Each feeding period lasted 35 days (28 days of adaptation followed by 7 days of sample collection).
  • This setup meant all dogs experienced all four diet treatments across the 140-day study.
• Doses: The four dry diets contained 0.00% (control), 0.07%, 0.14%, or 0.28% purified yeast beta-glucan.
• Outcomes measured:
  • Nutrient digestibility (especially crude protein)
  • Fecal microbiome via 16S rRNA sequencing
  • Fermentation products in feces (short-chain and branched-chain fatty acids, pH, lactate)
  • Immune indicators, including fecal IgA, blood cell phagocytosis and oxidative burst, and lymphocyte immunophenotyping (such as CD4+:CD8+ ratios).

What They Found

• Digestibility
  • Crude protein digestibility was higher at 0.14% and 0.28% than at 0.00% and 0.07%; other macronutrient digestibilities did not differ. The authors note crude protein content was modestly higher in the 0.14% and 0.28% diets, which may influence interpretation.
• Gut Microbiome
  • Beta diversity differed between 0.00% and 0.14%, indicating a community-level shift.
  • Relative abundance patterns at 0.14% included more Firmicutes (with increases in families like Ruminococcaceae and genera such as Faecalibacterium) and lower Proteobacteria, aligning with a profile often considered favorable in dogs. Figures and tables in the paper summarize these taxonomic changes.
• Immune Measures
  • Most immune readouts were unchanged in these healthy dogs. The CD4+:CD8+ T-cell ratio increased at 0.14%, which the authors interpret as a favorable immune balance signal.
• Safety And Tolerance
  • Dogs remained clinically healthy throughout; no vomiting or diarrhea episodes were reported, and body weight and condition were maintained.

Why This Matters Beyond Yeast

Although the intervention used a yeast-derived beta-glucan, the introduction explicitly situates beta-glucans as a shared family across yeasts and fungi. Many mushroom extracts also contain 1,3/1,6-linked beta-glucans, so these canine findings help illuminate how this linkage pattern can influence digestion, gut communities, and immune tone—even if the source here was yeast rather than a mushroom. Extrapolation to specific mushroom products still requires source-, extraction-, and dose-aware research.

Limitations And Future Directions

• The study involved healthy dogs; effects could differ in dogs with clinical conditions.
• Diets with 0.14% and 0.28% had slightly higher crude protein, which the authors acknowledge when interpreting protein digestibility.
• Fermentation endpoints (short-chain fatty acids, branched-chain fatty acids, pH, lactate) did not change, possibly due to rapid colonic absorption or the primarily immunomodulatory (rather than fermentative) action of purified beta-glucans.
• The sample size was small (n = 8), appropriate for a crossover but not powered for rare events or subtle subgroup effects. Larger, longer trials—including head-to-head comparisons of yeast- and mushroom-derived beta-glucans—would clarify source-specific impacts and optimal dosing.