Effect of dexamethasone in feed on intestinal permeability, differential white blood cell counts, and immune organs in broiler chicks.

We have previously shown that intestinal barrier function can be adversely affected by poorly digested diets or feed restriction, resulting in increased intestinal inflammation-associated permeability. Three experiments were conducted in broilers to evaluate the effect of dexamethasone (DEX) treatment on systemic fluorescein isothiocyanate-dextran (FITC-D; 3-5 kDa) levels, indicative of increased gut epithelial leakage. Experiment 1 compared DEX injections of 1 mg/kg, once per day on d 3, 5, and 9, with feed administration at 0.57, 1.7, or 5.1 ppm d 4 to 10, with FITC-D serum concentrations 2.5 h after gavage with 4.16 mg/kg FITC-D. All DEX treatments resulted in marked (2 to 6X; P<0.05) increased serum FITC-D levels. Feed DEX administration resulted in greater (P<0.05) gut permeability than injection at any dose, with numerically optimal effects at the lowest dose tested. In experiments 2 and 3, chicks were randomly assigned to a starter ration containing either control (CON) or DEX treated feed (0.57 ppm/kg; d 3 to 10 experiment 2, d 4 to 10 experiment 3). At d 10, all chicks were treated by oral gavage with FITC-D and serum samples were obtained as described above. Samples of the liver were aseptically collected, homogenized, diluted 1:4 wt/vol in sterile saline, and serial dilutions were plated on tryptic soy agar to evaluate total numbers of aerobic bacteria in the liver as an index of bacterial translocation (BT). In both experiments, FITC-D absorption was significantly enhanced (P<0.05) in DEX-treated chicks, again indicating increased paracellular leakage across the gut epithelium associated with dissolution of tight junctions. Experiment 2 differential cell counts showed an increased heterophil/lymphocyte ratio, and immune organ (spleen and bursa of Fabricius) weights for experiments 2 and 3 were decreased (P<0.05) from controls. In experiments 2 and 3, dietary DEX administration resulted in numerically (experiment 2) or significantly (P<0.05) increased enteric BT to the liver, supporting the observation that dietary DEX causes a stress-like inflammatory GI response, which may contribute to subclinical or clinical disease, and may be a useful model for ongoing disease mitigation research related to stress-related diseases of GIT origin.