Effect of partial replacement of soybean meal with high-temperature fermented soybean meal in antibiotic-growth-promoter-free diets on growth performance, organ weights, serum indexes, intestinal flora and histomorphology of broiler chickens

Abstract In order to investigate the effects of the dietary supplementation of high-temperature fermented soybean meal (HFSBM) without antibiotics on broiler chickens, a total of 270 one-day-old chicks were distributed ad libitum to 5 dietary treatments with 6 pen replications of 9 birds, consisting of two control treatments (basal diet (HFSBM0, 0 g kg-1) and basal diet plus antibiotics (Ant) and three HFSBM addition treatments (50, 100 and 150 g kg-1). After fermentation with Bacillus stearothermophilus, the crude protein, peptide and total phenolic contents in HFSBM significantly increased, while trypsin inhibitor activity decreased by 74% compared to soybean meal (SBM). Growth performance was determined on day 0, 21 and 42. After the 42-d feeding experiment, one chick from each pen was picked out for sampling on day 42. Samples of blood, heart, liver, spleen, thymus, bursa of Fabricius, duodenum, jejunum, ileum and cecum were collected for analysis. Dietary supplementation with HFSBM (50, 100 and 150) presented no significant influence on growth performance of broilers, but had positive effects on increase of relative weights of thymus and bursa of Fabricius, reduction of glutamic-oxaloacetic transaminase (GOT) level in serum, improvement of intestinal morphology and gut flora. Results showed that chicks fed with HFSBM-containing diets had an increasing tendency (P = 0.111 & 0.156) on the relative weight of thymus compared to HFSBM0 and Ant controls, and also an increasing tendency (P = 0.051) on the relative weight of bursa of Fabricius compared to the Ant (days 1-42). Meanwhile, the GOT level in serum reduced tendentiously (P = 0.112) compared to HFSBM0, while decreased significantly (P = 0.024) compared to Ant. The villus height to crypt depth ratio (V/C) of the duodenum was higher (P = 0.003 & 0.008) than that in chicks fed with HFSBM0 and Ant. The count of B. subtilis in jejunum digesta increased significantly (P = 0.001 & P = 0.001) compared to two controls, and the B. subtilis count in ileum digesta enhanced significantly compared to Ant. Furthermore, the E. coli populations of digesta in duodenum and cecum decreased significantly (P = 0.001 & P