Effects of live <i>Bacillus pumilus</i> SG154 or a <i>Lacticaseibacillus paracasei</i> 327 postbiotic on apparent total tract nutrient digestibility and the immune function and fecal characteristics, metabolites, and microbiota of healthy adult dogs

Probiotics and postbiotics have the potential to shift the gut microbiota, support gastrointestinal health, and enhance immune function, but must be tested for safety and efficacy in the target host. The Bacillus and Lacticaseibacillus genera have been shown to positively influence microbial balance and enhance immune response and immune function in humans and livestock. The objective of this study was to determine the effects of live Bacillus pumilus SG154 or a Lacticaseibacillus paracasei 327 postbiotic on dietary apparent total tract digestibility and the hematology, serum metabolites, fecal characteristics, metabolites and microbiota, and skin and nasal microbiota of adult dogs. Twelve healthy adult English pointer dogs (age = 6.38 ± 2.75 yr; body weight = 23.98 ± 4.61 kg) were used in a replicated 3 × 3 Latin square design to test the following treatments administered via gelatin capsules: 1) placebo (control; 250 mg maltodextrin/day); 2) live B. pumilus [5 × 109 colony-forming units (CFU)/day]; 3) L. paracasei postbiotic (100 mg; derived from 2 × 109 CFU). Each experimental period was 28 d in length, including a 22-d adaptation phase, 5-d fecal collection phase, and 1 d for blood collection, nasal swabs, and skin swabs. Data were analyzed using the Mixed Model procedure of SAS, with P < 0.05 being significant and P < 0.10 being trends. Neither B. pumilus nor L. paracasei influenced nutrient digestibility, food intake, fecal output, or fecal characteristics. Based on 16S rRNA gene sequencing, the relative abundance of fecal Actinobacteriota tended to be higher (P < 0.10) and the relative abundance of fecal Collinsella was higher (P < 0.05) in dogs fed B. pumilus than those fed L. paracasei and controls. Treatments appeared to alter skin bacteria as well, with the relative abundance of skin Erysipelotrichaceae UCG-003 being higher (P < 0.05) in dogs fed L. paracasei than in dogs fed B. pumilus. Skin Ligilactobacillus relative abundance was lower (P < 0.05) in dogs fed B. pumilus than in controls. The relative abundance of skin Peptoclostridium was higher (P < 0.05) in dogs fed L. paracasei than in controls. Most hematology measures were within the reference ranges for adult dogs and unaffected by treatment. Overall, our results demonstrate that consumption of the B. pumilus SG154 and L. paracasei 327 tested are well-tolerated and does not influence nutrient digestibility or fecal characteristics.