Effect of recycled litter on immune cells in the cecal tonsils of chickens

This experiment was conducted to study selected aspects of the gut immune response in broiler chicks reared on fresh or recycled litter that were fed diets with and without subtherapeutic antibiotic supplementation. All of the chicks were reared in pens that contained either fresh pine shavings (fresh litter) or litter that was recycled for 3 consecutive flocks (recycled litter). The experiment was a 2 × 2 factorial arrangement of treatments with 4 replicate pens (n = 4) per treatment. At 10 and 35 d of age, the cecal tonsils were analyzed for intestinal immune measurements. The cecal tonsils of birds reared on recycled litter had increased IL-1 mRNA (P < 0.01) and a lower percentage of CD4(+)CD25(+) cells at 10 and 35 d of age when compared with those of chicks reared on fresh litter. Birds fed diets supplemented with bacitracin had a reduction in CD4(+) cells (P = 0.01) at 10 d of age when compared with that of chicks that were not fed the antibiotic. The combination of bacitracin supplementation and fresh litter resulted in an approximate 10-fold increase in IL-10 mRNA (P = 0.01) at 10 d of age when compared with that of the unsupplemented chicks in fresh litter. Among those chicks that were not supplemented with bacitracin, the recycled-litter treatment resulted in 25-fold (P = 0.01) and 39-fold (P = 0.02) higher IL-4 mRNA levels at 10 and 35 d of age, respectively, when compared with those of the chicks reared on fresh litter. In conclusion, the intestinal immune response of birds reared on recycled litter is skewed toward an inflammatory response, whereas the fresh litter treatment was skewed toward an anti-inflammatory response. Bacitracin supplementation did not interact with the litter type to alter IL-1 mRNA levels in cecal tonsils, suggesting the low efficiency of bacitracin in alleviating the inflammatory response induced by recycled litter.