This study aimed to investigate the effects of varying levels of bacteriocin (nisin) supplementation on the growth performance, nutrient digestibility, small intestinal histomorphology, and caecal microbiota of broiler chickens. A total of 100 one-day-old male chicks were divided into four groups: a control group and three treatment groups receiving 150 mg, 300 mg, or 500 mg of nisin per kilogram of feed. Over the 35-day trial, all chicks had ad libitum access to feed and water. The results demonstrated that nisin supplementation significantly improved the birds’ growth performance (body weight gain and feed intake), nutrient digestion, and intestinal histomorphology, and positively modulated their caecal microbiota compared to the control group. While both 300 mg and 500 mg of nisin per kilogram yielded the most significant improvements in growth performance, intestinal histomorphology, and microbial balance, 300 mg/kg was determined to be the optimal and adequate supplementation level. In conclusion, this study suggests that nisin can safely replace traditional antibiotics as a growth promoter without compromising animal health.

(Submitted 24 February 2026; Accepted 17 June 2026; Published 26 June 2026)