Effect of period supplementation of Saccharomyces boulardii in humoral immune response of sheep immunized with recombinant chimera of Paeniclostridium sordellii

•S.boulardii supplementation improve P.sordellii vaccine response in sheep;.•A short or daily S. boulardii supplementation induces elevated specific IgG levels;.•S.boulardii supplementation modulate an early vaccine response to P. sordelii. Saccharomyces boulardii has emerged as a promising probiotic agent in bolstering the immune system. In vaccinology, its application can be explored to optimize vaccine efficacy by augmenting host immune response and consequently enhancing the immunogenicity of antigenic formulations. However, it is imperative to conduct further research to comprehend the effectiveness of this probiotic in novel vaccines targeting significant pathogens affecting animal health. Hence, this study investigated the effects of a short (3 - 5 days) or continuously (56 days) S. boulardii supplementation (3 × 108 CFU/mL) on the adaptive immunity of sheep immunized with a recombinant antigen against Paeniclostridium sordellii (rAPS). Four immunized groups (G1-G4) were evaluated, varying the regimen of S. boulardii supplementation. Elevated levels of anti-rAPS IgG immunoglobulins were detected in all vaccinated animals. Daily supplementation with S. boulardii (G1) resulted in higher IgG levels, reaching antibody titers of up to 25,600, which were 16 times higher than those observed in not supplemented group (G4) and 4 times higher than in the group supplemented for 3 days (G3) or 5 days (G2) before each immunization. These findings demonstrate that S. boulardii can enhance vaccine-induced immune responses against P. sordellii, particularly IgG-mediated immune responses in sheep. The possibility of a short supplementation for 5–3 days is a very important finding for animal husbandry, considering the supplementation and supply management cost.