The effects of Forsythia suspensa extract and berberine on growth performance, immunity, antioxidant activities, and intestinal microbiota in broilers under high stocking density

A 42-d experiment was conducted with 276 Arbor Acres broilers (1 d of age, weighing 41.1 ± 1.5 g) to determine the effects of Forsythia suspensa extract (FSE) and berberine (BE) on growth performance, immunity, antioxidant activities, and intestinal microbiota stocked at high stocking density (28 kg of BW/m(2) as the normal density, 46 kg of BW/m(2) as the high density). The feeding program consisted of a starter diet from d 1 to 21 of age and a finisher diet from d 22 to 42. Dietary treatments included (1) negative control group (NC), stocked at high density; (2) positive control group (PC), stocked at normal density; (3) FSE, NC + 100 mg/kg of FSE; (4) BE, NC + 100 mg/kg of BE; and (5) FSE + BE, NC + 100 mg/kg of FSE + 100 mg/kg of BE. Birds had free access to diets and water. Body weight and feed intake were measured at d 21 and 42. Blood, spleen and bursa, and intestinal contents were collected at d 42 for analysis. The results showed that growth performance did not differ among treatments in the starter period; however, in the finisher and overall periods, birds in FSE + BE, FSE, BE, and PC had greater final BW, ADG, and ADFI than the birds in NC (P < 0.05). The birds in FSE + BE, FSE, BE, and PC had greater bursa weight, bursa weight/BW ratio, serum total antioxidant capacity, and superoxide dismutase activity than birds in NC (P < 0.05). The FSE + BE, FSE, and BE birds had lower serum malondialdehyde level than NC birds (P < 0.05). The FSE + BE, FSE, BE, and PC birds had lower counts of Escherichia coli but greater Lactobacillus in the cecum than that of NC birds (P < 0.05). Dietary supplementation with FSE, BE, or both can improve the growth performance possibly by enhancing immunity, reducing oxidative stress, and promoting intestinal colonization by healthy microbiota of broilers under high stocking density.