Abstract
BACKGROUND: The importance of glucan additives has been widely recognized in farm animals. Yet the precise role of POLYCAN, a β-glucan derived from the black yeast Aureobasidium pullulans SM-2001, remains limited in companion animals. Therefore, this study aims to evaluate its effect on performance, nutrient digestibility, hematology, and the gut microbiome and serum metabolites in beagle dogs. METHODS: Eight healthy male beagle dogs (8 months old; 10.70 ± 1.79 kg body weight; 3.00 ± 0.15 body condition score) were enrolled in a 10-week study comprising two phases: Phase 1 (weeks 0-4) and Phase 2 (weeks 6-10), separated by a 2-week washout period. The dogs were divided into two groups and fed a control (CON), basal diet and CON diet supplemented with 1,000 mg/d of POLYCAN. Each of two diets were provided using a cross over design for eight weeks, with four beagles assigned to each treatment. During the washout period, all dogs were fed only the commercial basal diet. RESULTS: Throughout the experimental period, POLYCAN supplementation did not affect growth performance, nutrient digestibility, or fecal pH in beagles. However, serum calcium, insulin-like growth factor-1 (IGF-1), growth hormone, and immunoglobulin G (IgG) concentrations were significantly higher (P < 0.05) in the POLYCAN-supplemented group. Alpha-diversity indices of microbial richness and evenness, as well as beta-diversity based on Bray-Curtis dissimilarity and unweighted UniFrac distances, showed no significant differences between treatment group. At the phylum level, Actinobacteria and Proteobacteria were more abundant in the POLYCAN group, followed by Fusobacteria and Bacteroidota. At family level, Lachnospiraceae, Ruminococcaceae, Coriobacteriaceae, Lactobacillaceae, Peptostreptococcaceae, and Erysipelotrichaceae exhibited higher relative abundances. Furthermore, the core gut microbiota at genus level was dominated by Micrococcus and Fusobacterium. Untargeted metabolomic analysis also revealed distinct group separation, identifying key metabolites including lumichrome, D-mannitol, and 2'-deoxycytidine. Pathway enrichment analysis indicated alterations in pyrimidine, histidine, and bile acid metabolism with higher metabolite abundance observed in the POLYCAN-treated group. CONCLUSION: Overall, our findings validate that adding 1,000 mg/d POLYCAN to canines' diet could serve as a functional nutraceutical to enhance their immune and gut health without affecting growth and digestion.