277. Associations Between Protein Processing and Digestibility, Gut Microbiota Diversity, and Abundance in Dogs.

Abstract Considering that nitrogen-derived metabolites produced during proteolytic fermentation may influence microbial ecology, dietary protein source and digestibility can alter the availability of nitrogenous substrates reaching the large intestine and microbial metabolism [1]. Although highly digestible diets are traditionally regarded as indicators of nutritional quality, little is known about the effects of very highly digestible diets, such as hydrolyzed protein–based diets, on the canine microbiome [2,3]. Targeted microbiota assessment using quantitative PCR (qPCR) enables absolute quantification of clinically relevant bacterial taxa and may improve the interpretation of microbiome responses in nutritional studies. Therefore, this study evaluated associations among protein hydrolysis and digestibility, extrusion conditions, biogenic amines (BA) intake, and fecal microbiota composition in healthy dogs fed extruded diets. Three formulations with increasing substitution of conventional poultry by-product meal by hydrolyzed poultry by-product meal (HPM; 0, 50, and 100%) were processed under two levels of specific mechanical energy (low: 10 kWh/t, mass temperature 100 °C; high: 25 kWh/t, 150 °C), totaling six treatments. Maillard compounds (MC) formation and BA were evaluated in the diets. Eight dogs per diet were used to evaluate digestibility, fermentation products, and microbiota composition quantified by qPCR. Microbial values were used to calculate the dysbiosis index (DI) (Ethics Committee approval 003799/23). Associations between nutritional variables (protein digestibility, ingested BA, and MC) and microbial taxa were assessed using Spearman correlation with false discovery rate correction (P < 0.05). Crude protein digestibility was positively correlated with the canine DI (r = 0.48; adjusted P = 0.031) and Streptococcus abundance (r = 0.44). These findings partially contrast with previous reports showing that lower protein digestibility increased dysbiosis-related taxa [4]. In the present study, digestibility values were generally higher, which may explain these differences. Ingested BA were also positively correlated with DI (r = 0.42) and Streptococcus abundance (r = 0.46), suggesting that dietary BA intake may influence microbiota composition. MC intake did not affect microbial composition (P > 0.05). Notably, increased DI and Streptococcus abundance occurred in only a subset of animals, indicating that these associations may reflect inter-individual variability rather than a consistent dietary effect. Although variable among dogs, higher protein digestibility and increased BA intake were associated with higher DI values in healthy animals. These results suggest that microbial responses to dietary nitrogen metabolism may be relevant when evaluating protein sources in canine nutrition. Acknowledgments: BRF Feed, BRF Ingredients and Stonewell Gastrointestinal Vet. [1] Pinto CFD et al. (2022) PLoS ONE 17(7): e0271932 [2] Felix AP et al. (2022) Anim Feed Sci Technol 283:115183 [3] Suchodolski JS (2021) Vet Clin Pathol. 2022;50(Suppl.1):6–17 [4] Souza RBMS et al. (20)