Groups. SPF P2a line (B19/ B19) white Leghorn chickens eggs were obtained from Cornell University, Ithaca, NY. The eggs were hatched in the University of Connecticut Poultry Farm and after the hatch, the chickens were moved to the Office of Animal Research Services (OARS) facilities. After 2 weeks in the brooders with free access to water and a standard starter diet, the chickens were divided into groups, bled for baseline serology, transferred to isolators equipped with high-efficiency particulate air (HEPA) filters, and were provided commercial diets and water ad libitum.