Impact of Bacillus and Lactobacillus probiotics on growth performance, stress indices, and ileal histomorphology in broilers under high stocking density

This study evaluated the impacts of Bacillus and Lactobacillus probiotics on broiler chicken growth performance, carcass traits, stress responses, and intestinal health at high stocking density. A total of 200 one-day-old broiler chicks (Cobb 500) were randomly assigned to five equal groups (4 replicates with 10 chicks per replicate) as follows: 1) LSD: low stocking density; 2) HSD: high stocking density; 3) HSDBacil: high stocking density with Bacillus probiotic; 4) HSDLAB: high stocking density with Lactobacillus probiotic; and 5) HSDMix: high stocking density with combined Bacillus and Lactobacillus probiotic. The LSD- and HSD-broilers were subjected to 12.5 and 16 birds/m2 stocking density, respectively. Growth performance, carcass traits, serum cortisol levels, oxidative stress markers, and ileal histomorphology were measured. The results indicated that body weight, body weight gain, and the weights of Fabricius bursa and breast meat were also adversely affected by high stocking density. Probiotic administration, particularly Bacillus-based probiotic, increased body weight, body weight gain, and breast meat weight. Elevated serum cortisol and malondialdehyde levels, as well as decreased serum levels of total antioxidant capacity in the HSD group, confirmed the presence of heightened stress and oxidative damage, which were significantly reduced by probiotic administration. In addition, improvements in ileal histomorphology, including increased villus height and crypt depth, were observed in the probiotic-treated groups. Results indicated that the Bacillus-based probiotic had a stronger impact on attenuating the undesirable effects of high stocking density in broilers and can be used as a beneficial nutritional additive against stressful conditions.