Dietary yeast beta 1,3/1,6 glucan supplemented to adult Labrador Retrievers alters peripheral blood immune cell responses to vaccination challenge without affecting protective immunity

Yeast-derived 1,3/1,6 beta-glucans may alter host immunity to produce robust and quickly resolved responses that align with companion animal health goals. In adult dogs, immunomodulation by yeast 1,3/1,6 beta-glucans in extruded kibble diet have not been well documented. The study objective was to evaluate systemic immune responses in dogs fed kibble diets with two yeast 1,3/1,6 beta-glucans doses before and after vaccine challenge. Twenty-four adult Labrador Retrievers were assigned to three dietary treatments consisting of a basal diet (control) supplemented with 0.012% or 0.023% (0.5 or 1x, respectively) yeast 1,3/1,6 beta-glucan with equal sex representation within each treatment (8 dogs/diet). Animals were fed experimental diets for a 29-d acclimation period, after which baseline blood samples were collected before administration of a combination canine distemper virus, parvovirus, and adenovirus-2 vaccine. Blood samples were collected weekly for 21 d following vaccination with whole blood for CBC analysis, serum for titer and cytokine assays, and peripheral blood mononuclear cells (PBMC) isolated for flow cytometric immune cell profiling. Data were analyzed using the MIXED procedure with diet and timepoint fixed effects. Serum titer was analyzed by Kruskal-Wallis test (SAS 9.4; P <= 0.05). Prior to vaccination, beta-glucan diets did not affect serum cytokines, antibody titer, or immune cell populations. In the first 7 d post-vaccination (dpv), PBMC CD21(low) B cells increased 36.5% to 58.1% in all groups but the magnitude of change was lesser in the 0.5x beta-glucan diet resulting in 25.6% lower CD21(low) populations compared to control-fed dogs (P = 0.007). By 21 dpv, B-cell populations recovered to baseline levels in dogs fed 1x beta-glucan, but CD21(high) cells remained elevated 50.5% in dogs fed 0.5x beta-glucan diets compared with baseline (P < 0.0001). While no differences in serum titer or cytokines were observed, feeding both beta-glucan diets maintained stable blood monocytes, whereas a 53.0% decrease between baseline and 14 dpv was observed in control-fed dogs (P = 0.01). Collectively, these outcomes suggest that a 1x dose of 1,3/1,6 yeast beta-glucan in extruded kibble diets altered monocytes associated with trained immunity, did not reduce PBMC CD21(low) B-cell responsiveness, and simultaneously contributed to B-cell population resolution by 21 dpv in adult dogs. Additional research to assess the functionality of these changes is needed.