Dietary Gloiopeltis tenax Is Associated with Shifts in Fecal Microbiome and Serum Metabolome Profiles in Healthy Adult Dogs

Gloiopeltis tenax is a red seaweed containing diverse polysaccharides and bioactive compounds with potential functional applications in animal nutrition. However, information regarding its physiological and microbiome-associated effects in companion animals remains limited. The present study was designed as an exploratory nutritional intervention to evaluate physiological responses associated with dietary G. tenax supplementation in healthy adult dogs using an integrated framework including nutrient digestibility, glycan-degrading enzyme activity, fecal microbiome profiling, and serum metabolomics. Ten healthy adult dogs were assigned to two dietary groups receiving nutritionally balanced diets containing either Ulva sp. (CON) or G. tenax (GT) at 1% inclusion for 16 weeks under standardized feeding and housing conditions. Nutrient digestibility, fecal glycan-degrading enzyme activities, fecal microbiome composition, predicted microbial functional profiles, and serum metabolomic responses were evaluated. No significant differences were observed in nutrient digestibility, fecal score, or general health-related parameters between groups, suggesting acceptable tolerability of dietary G. tenax under the present experimental conditions. Relative abundances of several bacterial taxa differed between groups, and glycan-degrading enzyme activities showed directional changes associated with dietary treatment. PICRUSt2-based analyses suggested potential differences in predicted carbohydrate- and glycan-associated microbial functional tendencies between groups. Serum metabolomic analysis additionally revealed alterations in several amino acid- and carbohydrate-related metabolites associated with dietary intervention. Collectively, these findings provide preliminary insight into microbiome- and metabolome-associated responses to dietary G. tenax supplementation in dogs. Although limited by the exploratory nature and relatively small sample size of the present study, the integrated multi-omics approach applied here may contribute to the development of functional evaluation frameworks for companion animal dietary ingredients. Further studies with larger cohorts and expanded functional analyses are warranted.