Investigation of the Effects of Using Natural Fermented Lactic Acid Bacteria as Probiotics on Fattening Performance, Blood Parameters, and Intestinal Microflora in Broiler Chickens Under Heat Stress

Heat stress is a major environmental challenge in poultry production, negatively affecting growth performance, physiological functions, and intestinal health in broiler chickens. This study aimed to investigate the effects of probiotics prepared from meadow grass with molasses (PJFM) and commercial probiotics (TP) on fattening performance, blood parameters, and intestinal microflora in broiler chickens under heat stress. A total of 240 one-day-old Ross 308 broiler chicks (initial body weight: 46.72 ± 0.18 g) were used in a 42-day trial. The chicks were divided into six groups of 10 birds each, with four replicates. The study groups were divided into six groups: control (TNC) under normal environmental conditions (TN), PFJM (TNPJFM) and commercial probiotic (TNTP) supplemented in their drinking water, and control (HSC), HSPFJM, and HSTP under heat stress (HS) conditions. Temperature (34.5–36.2 °C) was applied for 42 days. Lactic acid bacteria (LAB) were 1.2 × 1012 cfu/mL in PFJM, and Lactiplantibacillus plantarum was the predominant species. Probiotics were added to the chicks’ drinking water at 0.5 mL/L. The control groups’ water was free of probiotics. This study revealed a decrease in body weight and body weight gain and a worse feed conversion ratio in the HSC group. The lowest carcass weight under heat stress was in the HSC group, and the highest was in the HSPFJM group. The lowest gizzard and highest bursa Fabricius percentages were in the probiotic-containing groups. Blood glucose and uric acid decreased in the HSPFJM group. In the HSC group, lactic acid bacteria (LAB) decreased, while E. coli, total mesophilic aerobic bacteria (TAB), enterobacteria, and yeast increased. In the probiotic-supplemented groups, LAB increased, while E. coli, yeast, and enterobacteria decreased. The study results suggest that PJFM supplementation may positively impact intestinal health in chickens exposed to heat stress, supporting growth performance and health parameters.