The commercial Saccharomyces cerevisiae fermentation product XPC™, often used as feed additive in poultry production, has been associated with enhanced immune functions. We evaluated immune responses and protection after IBV challenge in naïve and infectious bronchitis virus (IBV)- vaccinated specific-pathogen-free white leghorn chickens (groups n=50 each) receiving XPC at feed-additive concentrations of 2 lb/ton or 3 lb/ton.
Naïve chickens receiving XPC and challenged at 21 days of age showed reduced respiratory signs and a tendency of less histological damage in the trachea 5 days after challenge. Treated birds also showed increased IgA+ and CD44+CD8+ lymphocytes in the spleen 10 days after challenge. Viral load in the trachea, serum IBV antibody levels, and numbers of splenic CD3+/CD8+ and CD3+/CD4+ lymphocytes did not show significant differences between treated and untreated challenged controls. In experiment 2, birds received the same XPC treatments but were vaccinated with a live attenuated IBV vaccine at 10 days of age and subjected to homologous challenge at 25 days of age. Evaluations performed 5 days after challenge showed reduced adverse respiratory reactions and significantly increased IgM+ and IgA+ lymphocytes in the Harderian gland in XPC treated chickens.
XPC-treated chickens also showed significantly increased serum IBV antibody levels 20 and 27 days post challenge. Tracheal histopathology and viral load, and numbers of spleen CD44+ and CD3+ cells did not differ significantly between treated and untreated challenged controls. Some of the differences in response to IBV vaccination and/or challenge observed between XPC-treated and untreated chickens provide evidence for a beneficial effect and thus merit further study.
Key Words: infectious bronchitis, chickens, immune response
*Abstract presented at the 2015 International Poultry Scientific Forum