Real-time PCR was used to detect Toll-like receptor 4 (TLR4) and Claudin-1
in jejunal mucosa. Feeding COS or chlortetracycline reduced (P b 0.05) feed conversion ratio. Villus length, villus
length/crypt depth, and goblet cells, were increased (P b 0.05), but villus width and crypt depth were decreased
(P b 0.05) in both COS and chlortetracycline groups.