Clinical and Faecal Outcomes in Adult Dogs with Chronic Enteropathy Fed an Hydrolysed Protein Diet with and Without Bacillus velezensis DSM 15544: A Randomised, Double-Blind, Cross-Over Trial

Chronic enteropathy (CE) is a common cause of persistent gastrointestinal signs in dogs, and dietary management represents the cornerstone of treatment. Probiotics have been proposed as adjunctive strategies to support intestinal health, although evidence of their efficacy remains limited. This randomised, double-blind crossover trial evaluated the effects of a hydrolysed protein diet supplemented or not with Bacillus velezensis DSM 15544 applied during post-extrusion coating. Thirteen CE dogs were randomly assigned to receive the Diet with Probiotic (DIET+PRO) or the Diet without Probiotic (DIET) during two consecutive 60-day feeding periods, with parameters assessed at baseline (T0) and after 30 (T1) and 60 (T2) days of each dietary treatment. Clinical response was assessed using the Canine Inflammatory Bowel Disease Activity Index (CIBDAI) andfecal core (FS). Gut microbiota was evaluated by the qPCR Dysbiosis Index (DI) and 16S rRNA gene sequencing, including taxonomic composition, alpha and beta diversity analyses. Compared with baseline (CIBDAI: 4.2 ± 1.7; FS: 3.9 ± 1.5), both dietary treatments significantly improved clinical scores (CIBDAI: 1.3–1.5; FS: 2.2–2.3; p < 0.02), irrespective of probiotic supplementation. Neither microbiota composition, alpha diversity, beta diversity, nor the DI (−2.7 ± 2.3 to −2.1 ± 2.3) differed between dietary treatments. Clinical responses to B. velezensis DSM 15544 supplementation varied among dogs. Overall, the hydrolysed diet effectively improved gastrointestinal clinical signs in dogs with CE, whereas the effects of B. velezensis DSM 15544 remain unclear and warrant further investigation, as any additional benefit may have been masked by the marked clinical response to the hydrolysed diet.