Integrating bacteriophage with high-and low-protein feeding strategies enhances performance, gut health, and environmental sustainability in ROSS 308 broilers

A 35-day growth trial was conducted to evaluate the effects of dietary protein density and bacteriophage (BP) supplementation on growth performance, nutrient digestibility, gas emissions, organ development, meat quality, and ileal microbiome in ROSS 308 broilers. A total of 1,440 chicks (47.87 ± 1.50 g initial BW) were randomly allocated to four treatments in a 2 × 2 factorial design: high protein (HP) and low protein (LP) diets, with or without 10 mg/kg BP, each with 20 replicates of 18 birds. During the grower phase, birds fed diet supplemented with BP showed tendency (P < 0.1) to improved bodyweight gain (BWG) and feed conversion ratio (FCR). Also, during the finisher phase, birds receiving BP supplementation demonstrated a significantly greater (P < 0.05) BWG and a tendency toward increased feed intake. Furthermore, over the entire experimental period, final BW and cumulative BWG were significantly (P < 0.05) increased in birds fed BP supplementation. At the end of the trial, BP supplementation has tended to improve dry matter and significant increase in nitrogen digestibility. Moreover, ammonia emission was significantly(P < 0.05) reduced in birds fed LP diets. Furthermore, alpha diversity of evenness, Chao1, observed features, Shannon's, Simpson's, and Pielou's indices were highly abundance in birds fed LP diet with BP. Principal coordinate analyses indicated treatment-dependent clustering, with LP+ showing the most distinct separation from HP groups. At phylum level, HP groups exhibited a higher proportion of Bacteriodia compared with LP groups. Whereas phyla firmicutes were more abundant in LP following Desulfobacterotax. At genus level LP- group showed a greater proportion of Bacteroides spp., Faecalibacterium, and Prevotellaceae. Based on the results, we infer that incorporating bacteriophage into broiler diets can serve as a sustainable nutritional strategy to optimize performance, nutrient utilization, and environmental efficiency across varying protein levels.