Collagen content and collagenase concentration in the gut tissue of chickens. Chickens were fed a control diet (CON), CON supplemented with 15 g of hemp extract (CBD)/kg of diet, CON supplemented with 0.5 mg of nanosized selenium particles (Nano-Se)/kg of diet, or CON supplemented with both additives (CBD + Nano-Se). At 15, 16, 17 and 18 days of age, the chickens in each experimental group and the positive control (CON-positive) group were orally infected with 1 mL of 108 CFU/mL C. perfringens inoculate. A coccidial cocktail (1 mL) was administered before C. perfringens challenge to all chickens. a,b,cThe different letters indicate significant differences (P < 0.01). The error bars indicate the mean standard error values for the 8 chickens in each dietary treatment group.