Beta 1-3, 1-6 Glucan Supplementation Modulates the Immune Response of Horses Undergoing a Glucocorticoid Challenge

An appropriate immune response is critical to the maintenance of systemic health across species. Specifically related to the horse, pathogenic exposure, exercise or travel-induced stress, age, and metabolic status may play a role in the development of disease. Yeast-derived beta glucans have been implicated for their role in modulating the immune response. The objective of the study was to evaluate the potential for a beta 1-3, 1-6 glucan supplement to modify the immune response in horses challenged through a glucocorticoid induced model of immune suppression. It was hypothesized that supplemented horses would have an improved immune response to a glucocorticoid challenge as demonstrated by immune cell proliferation and activation. Sixteen horses were randomly assigned to one of four groups, a base diet (Purina® Strategy® fed at 0.5% BW) with no supplementation (CON; n=4), base diet + 1 mg/kg BW beta glucan (LOW; n=4), base diet + 2 mg/kg BW beta glucan (MID; n=4), and base diet + 4 mg/kg BW beta glucan (HIGH; n=4). Horses were acclimated to the experimental rations for 2 d and then received supplementation for 15 additional days. Baseline blood samples were obtained following acclimation at d 0. A glucocorticoid challenge (0.1 mg/kg BW) was administered intravenously on d 15 and blood samples were obtained at 0, 8, 24, and 48 hr post challenge. Blood samples were analyzed for neutrophil and lymphocyte counts, serum ACTH and cortisol levels, lymphocyte subpopulation distribution (CD4⁺ T cells, CD8⁺ T cells, B cells, CD4/CD8 ratio), and leukocyte LFA-1 and MHC class II expression via flow cytometry. The data were analyzed via ANOVA to determine differences due to time and treatment and time by treatment interactions utilizing the GLIMMIX procedure in SAS 9.4 (Cary, NC). Glucocorticoid administration resulted in an increase in neutrophil and decrease in lymphocyte numbers at 8 hr post administration. Horses receiving beta glucan regardless of concentration displayed an increase in CD8⁺ T cells at 8 hr post glucocorticoid administration (P<0.01). Horses in the LOW group displayed an increase in Mo LFA 1 at 8 hr post challenge compared to CON and HIGH groups (P<0.01). Taken together, these data indicate that the immune challenge was successful in suppressing the immune response and beta glucan supplementation modulated the immune system during challenge. More research is necessary to fully elucidate the potential role of beta glucan supplementation on horse health.