1. A total of 648 one-day-old broiler chicks were randomly allocated into six equal groups to investigate the effect of diet supplemented with fermented Ginkgo biloba leaves (FGBL) at different levels on nutrient utilisation, intestinal digestive function and antioxidant activity. 2. Broilers in the six groups were offered basal diet supplemented with either 0, 1.5, 2.5, 3.5, 4.5 and 5.5 g/kg FGBL during the 42-d experiment, respectively. 3. Birds fed with 3.5 g/kg FGBL diet exhibited increased (P < 0.05) body weight gain, feed intake, apparent total tract retention (ATTR) of ether extract (EE) and relative weight of duodenum. Diets supplemented with FGBL increased (P < 0.05) antioxidant and digestive enzyme activities, and decreased malondialdehyde (MDA) concentrations at different degrees in pancreas and small intestine. The expression of antioxidant related genes was up-regulated (P < 0.05) by the transcription factor Nrf2 in small intestine, especially with supplementation of 3.5 and 4.5 g/kg FGBL in the diet. However, 5.5 g/kg diet significantly decreased (P < 0.05) feed conversion ratio and catalase activity (CAT) in the duodenum. 4. Body weight, relative weight of duodenum, amylase and trypsin activities in ileum, total antioxidant capacity (T-AOC) and CAT in duodenum, and glutathione peroxidase (GSH-PX) in ileum increased linearly and quadratically with FGBL content. Activities of amylase in pancreas, trypsin in jejunum, lipase in ileum, and GSH-PX in duodenum and jejunum increased linearly with FGBL content. Body weight gain, ATTR of EE, activities of trypsin in pancreas and amylase in jejunum, total superoxide dismutase activity in duodenum, T-AOC level and concentrations of MDA in the jejunum and ileum showed a quadratic (P < 0.05) dose response as supplemental FGBL level increased. 5. In conclusion, the addition of FGBL had the potential to improve nutrient utilisation, intestinal digestive function and antioxidant activity of broilers. The optimal dietary supplementation dose for broiler production seemed to be 3.5 to 4.5 g/kg.
Keywords: Antioxidant activity; Broilers; digestion; enzymes; gene expression; small intestine.