Dual effects of dietary protein restriction and probiotic supplementation on broiler performance and fecal gas emission.

This study aimed to evaluate the effects of dietary protein levels and the use of a probiotic cocktail (Bacillus subtilis and Bacillus licheniformis) on growth performance, apparent digestibility, fecal microbiota, blood profile, and fecal gas emissions in broiler chickens. A total of 225 one-day-old Ross 308 broiler chicks, weighing 48.10 ± 0.86 g, were used in a completely randomized design. Birds were randomly assigned to three dietary treatments, with five replicates per treatment and 15 birds per replicate. Experimental diets were formulated with two protein levels at each feeding phase: a low-protein (LP) diet and a high-protein (HP) diet. The three treatment groups included: (1) HP group (high-protein basal diet), (2) LP group (low-protein basal diet), and (3) LP-P group (low-protein diet supplemented with a probiotic mixture). The HP diet improved body weight and growth metrics compared to the LP diet. However, the LP-P group achieved similar or superior growth performance (ADG, BWG) and feed conversion ratio (FCR) to the HP diet, particularly during the 14-35 day period, indicating that probiotics compensated for the reduced protein content. Probiotics enhanced nitrogen digestibility and reduced ammonia and nitrous oxide emissions compared to the HP diet. Additionally, the LP-P group exhibited lower blood urea nitrogen levels, suggesting improved nitrogen metabolism. Probiotics also showed potential benefits in alleviating metabolic stress and modulating gut microbiota. These findings demonstrate that probiotic supplementation in low-protein diets can sustain broiler growth efficiency while reducing environmental impacts, offering a viable strategy for sustainable poultry production.