PS6-22. Dietary Modulation of Metabolism, Microbiome, and Stool Odor in Small Breed Dogs.

Abstract Background: Per Kleiber's Law, small breed dogs have higher per-kg energy needs and proportionally larger organs, along with reduced fermentation in the colon. To address these unique demands, this study evaluated the effects of a high-fat, low-starch food containing fermentable fibers and functional oils on small dogs' metabolism, microbiome, and stool odor. Methods: 40 small dogs were fed a Control food (3974 kcal/kg ME; 27% Protein/38% Fat/35% Starch+Sugars) and a Test food (4191 kcal/kg ME; 29% Protein/48% Fat/23% Starch+Sugars) in a 6-week crossover. Total dietary fiber, soluble fiber and insoluble fiber (% as fed) were: Control (7.6, 1.7, 5.9); Test (9.8, 1.0, 8.8). Foods analyzed by standard and AOAC methods (Eurofins). Fasting blood and stool were analyzed for metabolites (Metabolon, IDEXX), hormones (ELISA), and stool odor volatiles (GC-FID). Trial was run under IACUC-approved protocol CP966.0.0.0-A-C-D-ADH-MULTI-154-MULTI. Results: Dogs were fed to caloric requirement for healthy body weight; ME intake was equivalent between foods (p=NS). The Test food increased fasting fat metabolism: octanoate (+168%), octanoylcarnitine (+20%), and beta-hydroxybutyrate (+14%), while decreasing triglycerides (-29%) and lipemia (-75%). Anti-inflammatory omega-3 fatty acids increased significantly: 18:4n3 (+169%), 20:5n3 (+684%), and 22:6n3 (+297%). Clinical metrics for organ health decreased (improved): ALP (-19%), ALT (-18%), AST (-7%), and GGTP (-14%). Satiety hormone analysis showed decreased leptin (-11%) and PYY (-14%), with a decreasing trend for amylin (-16%); however, ghrelin increased (+102%). Total detectable odiferous stool volatiles decreased (-40%), driven by reductions in esters (-89%), aldehydes (-76%), ethers (-51%), alcohols (-49%), and acids (-38%), whereas those with benzene-type moieties increased (+65%). Fecal microbiome tryptophan metabolism shifted: processing via the TnaA pathway (e.g. indole) increased (+75%), while disposition via the ArAt+FldBC pathway (e.g. indolelactate) decreased (-69%), which increased the TnaA:ArAt+FldBC ratio (+292%). Conclusions: Formulating a food with higher protein/fat, reduced digestible carbohydrate, along with functional ingredients that include fibers as well as anti-inflammatory and ketogenic oils supports the specialized physiology of small breed dogs. This approach increases reliance on fat metabolism, reduces markers of organ stress, alters satiety hormones, decreases offensive stool odor volatiles, and shifts microbiome tryptophan metabolism.