Effects of yeast products on immune response and intestinal health of dogs and mice
With growing pet populations and the trend of pet humanization, the demand for functional ingredients that provide health benefits beyond basic nutrition has continued to increase in the pet food industry. Yeast products may serve as functional ingredients due to their potential health benefits as shown in livestock and rodents. Previous studies in dogs demonstrated some positive results of yeast supplementation in terms of modulating a few specific fecal microbiota and immune cell numbers, but little is known regarding the effects of yeast products on immune cell responsiveness, fecal microbiota profiles, and gut integrity. Herein, we aimed to test yeast products and hypothesized that they may provide health benefits and serve as functional ingredients in dog diets by enhancing immune response and promoting intestinal health. The first aim was to evaluate the effects of a Saccharomyces cerevisiae fermentation product (SCFP) on apparent total tract digestibility (ATTD), fecal characteristics, fecal fermentative end-products, fecal microbiota, immune cell populations, immune cell responsiveness, and diet palatability of healthy adult dogs. Twelve healthy adult female beagles (mean age = 3.3 ± 0.8 yr; mean BW = 10.3 ± 0.68 kg) were fed the same diet, but supplemented with 3 levels of yeast fermentation products (125, 250 or 500 mg/d) or a placebo (125 mg sucrose/d) via gelatin capsules in a replicated 4  4 Latin square design. A standard 2-d palatability test also was conducted to examine the palatability of a yeast-containing diet (0.2% of diet). Yeast supplementation did not affect ATTD, fecal characteristics, or fecal fermentative end-products, including short-chain fatty acids, branched-chain fatty acids, indole, and ammonia. Total white blood cell counts were decreased (P < 0.05) by SCFP. The percentage of NK cells and antigen-presenting cells were not altered by SCFP. However, when comparing control vs. all SCFP treatments, SCFP-supplemented dogs had greater (P < 0.05) MHC II-presenting B cell and monocyte populations than control dogs. IFN-γ secreting helper and cytotoxic T cells increased (P < 0.05) linearly with SCFP consumption. Immune cells derived from SCFP-supplemented dogs produced less (P < 0.05) TNF-α than those from control dogs when cells were stimulated with agonists of toll-like receptors (TLR) 2, 3, 4 and 7/8. A linear increase (P < 0.05) in serum IgE with SCFP dosage was noted. In the palatability test, a 1.9:1 consumption ratio was observed for the SCFP-containing diet vs. control diet, demonstrating a preference (P < 0.05) for SCFP. The second aim was to investigate the effects of a yeast product composed of yeast active components (YAC) on ATTD, fecal characteristics, fecal microbiota, and immune responses of healthy adult dogs. Twelve healthy adult female beagles (mean age: 4.8  0.9 yr; mean BW: 13.3  0.7 kg) were fed the same diet but supplemented with YAC (165 mg/d) or a placebo (125 mg cellulose/d) via gelatin capsules in a crossover design. Yeast treatment did not alter (P > 0.05) ATTD, fecal characteristics, or fermentative end-products. Microbial alpha- and beta-diversity and specific microbial taxa were not affected by treatment (P > 0.05). Immune cell populations and immune cell responsiveness of TLR were not altered by treatment (P > 0.05). The third aim was to study the effects of a yeast cell wall fraction on fecal characteristics, fecal microbiota, and indices related to gut integrity and immunity of adult dogs undergoing an abrupt dietary shift. Twelve adult female beagles (mean age: 5.16  0.87 yr; mean body weight: 13.37  0.68 kg) were used in a replicated 4  4 Latin square design with four 28-day experimental periods. During days 1-14 of each period, dogs were fed a dry kibble diet and supplemented with a placebo (cellulose; 125 mg/d) or yeast cell wall fraction (365 mg/d). During days 15-28 of each period, dogs remained on their placebo or yeast treatments, but were rapidly transitioned to a canned diet or high-fiber diet. After diet transition, dogs supplemented with yeast cell wall fraction tended to have greater (P = 0.06) fecal IgA than controls. Fecal characteristics, fecal E. coli and C. perfringens, fecal calprotectin, and serum lipopolysaccharide-binding protein, however, were not affected (P > 0.05) by yeast treatment. Consumption of SCFP reduced immune cell responsiveness and positively affected microbiota in dogs, suggesting that it may be protective against intestinal diseases such as inflammatory bowel diseases. Therefore, the fourth aim was to evaluate the effects of SCFP on cecal and fecal microbiota, colonic gene expression and colonic histopathology in a dextran sulfate sodium (DSS)-induced colitis model. Fifty-four 6-week-old male C57BL/6J mice were assigned to one of three treatment diets (n = 18/diet): 1) AIN93G diet (control); 2) control diet + 5% SCFP; or 3) control diet + 5% psyllium husk (PH). After 2 wk, mice on each diet then were split evenly into groups that were provided with water or water + 3% (wt:vol) DSS for 5 d. Consumption of SCFP increased (P < 0.05) species richness of the gut microbiota and relative abundance of Butyricicoccus in fecal and cecal samples. Principal coordinates analysis of weighted and unweighted Unifrac distances of fecal and cecal microbiota revealed that PH mice clustered together (P < 0.05) and away from control or SCFP groups. Additionally, PH mice overall had greater (P < 0.05) gene expression of Cldn2, Cldn3, Cldn8, and Ocln compared to control mice. Disease activity index, immune cell numbers, colonic histopathology, and colonic gene expression were not affected (P < 0.05) by SCFP in DSS mice. DSS mice consuming PH had lower (P < 0.05) disease activity compared to control or SCFP mice. Overall, our results suggest that yeast supplementation may be beneficial for adult dogs by positively altering gut microbiota, enhancing immune capacity, reducing inflammation, and modestly promoting gut immunity. Given these benefits, yeast products may be included in dog diets as functional ingredients. However, not all yeast products tested here led to positive results in healthy dogs. Additionally, the yeast product SCFP failed to protect mice from DSS-induced colitis. The benefits of consuming yeast products may depend on their source, nutrient composition, presence of bioactive components, and dosage. Moreover, animals more prone to illness, such as dogs undergoing stress or immune challenge, or dogs susceptible to gastrointestinal distress (e.g., weanlings, geriatrics), may be benefited the most from consumption of such products.
University of Illinois - Urbana-Champaign
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