Probiotic Response to Limosilactobacillus reuteri DSM 32203 in Two Small-Breed Dogs Differing in Body Size

Probiotic effects in dogs may depend not only on the bacterial strain but also on host-related characteristics. Differences in body size are associated with distinct gastrointestinal and microbial features that may influence responses to nutritional interventions. This study evaluated the effects of Limosilactobacillus reuteri DSM 32203 in healthy small-breed dogs and investigated whether responses differed between Chihuahua and Dachshund dogs with different body weights. Healthy adult dogs were supplemented daily with L. reuteri DSM 32203, and body weight, body condition score, fecal score, fecal moisture, total lactobacilli, and total coliforms were evaluated throughout the study. Supplementation improved fecal quality, with increased consistency and reduced moisture, and fecal scores reaching or approaching the optimal value. An increase in total lactobacilli and a reduction in total coliforms was also observed. These findings are consistent with previous observations obtained with the same strain in other canine breeds. However, the magnitude of the reduction in total coliforms differed from that observed in our previous studies in larger breeds. Because breed, body size, and diet were not independently controlled, these cross-study differences cannot be directly attributed to body size alone. Although body size cannot be established as a direct causal factor due to potential confounding factors such as dietary differences, these findings provide preliminary evidence that host phenotypes may contribute to probiotic responsiveness.