A Saccharomyces cerevisiae Fermentation Product (Olimond BB) Alters the Early Response after Influenza Vaccination in Racehorses

Simple Summary Vaccination is one of the most important prophylactic methods for the prevention of disease in veterinary medicine. The initial post-vaccination events are dominated by innate immune mechanisms leading to a coordinated activation of specific adaptive immune responses. Thus, antibody production and induction of specific T cells depend on early post-vaccination events, triggered by vaccine ingredients and guided by factors released from initially targeted tissues and cells. The aim of this study was to analyse whether feeding a pre- and postbiotic feed supplement modulates such early immune responses after vaccination. Horses were fed a supplement (Olimond BB) based on products of fermented yeasts (Saccharomyces cerevisiae) for 8 weeks and subsequently vaccinated against influenza. Circulating leukocyte counts and their subpopulations were determined before and 24 h after vaccination. In absence of vaccination-induced side effects, horses receiving the supplement differed from control horses in the composition of neutrophilic granulocytes, CD4(+) cells, and reticulocytes. Thus, the pre- and post-biotic feed supplement modulated early innate immune mechanisms after vaccination. Saccharomyces cerevisiae (S. cerevisiae) fermentation products (SCFP) are used in animal husbandry as pre- and postbiotic feed supplements. A variety of immunomodulatory effects are noted in many species. The purpose of this study was to test the hypothesis that horses fed with SCFP containing feed additive Olimond BB display a modulated early immune response after influenza vaccination. Six horses received Olimond BB pellets (OLI) and five horses were fed placebo pellets (PLA) for 56 days. On day 40 all horses were vaccinated with a recombinant influenza A/equi-2 vaccine. At the day of vaccination, the groups did not differ in the composition of leukocyte subpopulations and reticulocytes. Twenty-four hours after vaccination total leukocyte counts and numbers of CD4(+) T-cells significantly increased in both groups. In PLA horses, the numbers of neutrophil granulocytes significantly increased and numbers of CD8(+) T-cells decreased, whereas the numbers of these cell types remained unchanged in OLI horses. Only OLI horses displayed a significant increase in reticulocyte percentages after vaccination. The numbers of lymphocytes, monocytes, CD21(+) B-cells, and serum amyloid A levels remained unaffected in both groups after vaccination. Sixteen days after vaccination, PLA and OLI horses differed significantly in their enhanced ELISA IgG titres against Newmarket and Florida Clade 1 influenza strains. The observed differences after vaccination suggest that feed supplementation with Olimond BB leads to modulated early immune responses after influenza vaccination, which may also affect the memory responses after booster vaccination.