The gut microflora play a crucial role in several physiologic functions of the host, including maturation of the gut-associated lymphoid tissues during the first months of life. Oral administration of probiotic lactic acid bacteria (LAB) modulates the immune system of humans and some laboratory animals. This effect has never been examined in dogs; therefore, our aim was to study the capacity of a probiotic LAB to stimulate immune functions in young dogs. Puppies were allotted to two groups receiving either a control diet or a diet supplemented with 5 × 108 (SF68) from weaning to 1 y of age. Fecal and blood samples were collected from the dogs at different time points for the measurement of fecal immunoglobulin (Ig)A, circulating IgG and IgA, and the proportions of lymphoid cell subsets. Fecal IgA and canine distemper virus (CDV) vaccine–specific circulating IgG and IgA were higher in the group receiving the probiotic than in controls. There were no differences in the percentages of CD4+ and CD8+ T cells between the groups, but the proportion of mature B cells [CD21+] was greater in those fed the probiotic. These data show for the first time that a dietary probiotic LAB enhance specific immune functions in young dogs, thus offering new opportunities for the utilization of probiotics in canine nutrition.
In conclusion, the results reported in this study support an adjuvant effect of Enterococcus faecium SF68 at both mucosal and systemic levels in puppies, an effect that could be relevant for improving protective immune responses against various infections during the critical weaning period as well as at later stages in life. This is particularly relevant if the long-term (up to 1 y of age) effect on antibody responses is considered. The precise mechanisms by which SF68 stimulates immune functions and boosts immune responses to a vaccine clearly deserve further investigation.