One hundred fifty 1-d-old broiler chickens (Ross breed) were used in this study. All broiler chickens used in this study had received normal vaccinations including Marek’s disease (turkey herpes virus (HVT), SB-1 and Rispen) in ovo at 18 d of incubation, and Newcastle disease (ND) and infectious bronchitis (IB) via coarse spray after hatch at the local hatchery. Upon arrival, they were vaccinated orally with Pfizer Inovocox vaccine, randomly placed (n = 25/group) on fresh, used, or GD litter, and fed a diet containing DFM-enriched or DFM-free diet. Diet and water were provided ad libitum basis. All experimental protocols were approved by the Small Animal Care Committee of Beltsville Agricultural Research Center and the University of Delaware.