The preventive oral supplementation of β-glucan at a dose of 10 mg/kg/day for thirty days modulates the immune response, as evidenced by an increase in serum total proteins, globulins, IL-8, and changes in the type of peritoneal inflammatory cells, without effectively attenuating the clinical signs of endotoxemia in horses. This evidence concerns the gene CXCL8 and serum lipopolysaccharide activity.