| Four trials were conducted to investigate the application of yeast culture (Diamond V XP Yeast Culture, YC) in broilers and its possible mechanism. Trial 1 was conducted to evaluate the effects of supplemental YC in broiler diets on performance, nutrient digestibility, mucosal development, and immunomodulatory functions. One-d-old Abor Acres chicks (n = 960) were randomly assigned to 1 of 4 dietary treatments, and fed the diets containing 0, 2.5, 5.0 and 7.5 g/kg of YC. Dietary supplemental YC at 2.5 g/kg improved average daily gain (ADG) and feed conversion during grower and overall periods (P≤0.05). Villus height to crypt depth ratios in the duodenum and jejunum (d 42) and ileum (d 21) were increased (P≤0.05) in broilers fed 2.5 g/kg of YC. YC supplementation increased digestibilities of Ca (linear and quadratic, P = 0.01) and P (linear, P = 0.01), antibody titers to Newcastle disease virus (linear, P≤0.05), serum lysozyme activity (linear and cubic, P≤0.05) and IgM (linear, P≤0.05), sIgA concentration in the duodenum (linear, P = 0.01) and amount of IEL (intraepithelial lymphocyte) in duodenum (linear, P<0.05). Trial 2 was conducted to investigate the effects of dietary YC on immune function of Eimeria tenella-infected broilers. Three hundreds and sixty 1-day-old male Abor Acres broiler chicks were randomly allotted into a 3×2 factorial arrangement with 3 levels of yeast culture (0, 0.25% and 0.50%) and 2 types of stimulation (saline or Eimeria tenella-infection). On d 21, half of birds were orally inoculated with 8×104 sporulated oocysts of Eimeria tenella in 0.3 mL of water. Coccidial infection decreased ADG of broilers (P=0.09), and dietary supplemental YC improved ADG (P<0.01). Addition of YC in diets increased percentage of CD3+, CD4+, CD8+ T lymphocytes (P<0.05) and CD4+/CD8+ ratio in peripheral blood and spleen. Both coccidial infection (P<0.1) and YC supplementation in diets (P<0.01) increased the amount of IEL, sIgA content in cecal tonsil and serum lysozyme content. Supplementation of YC increased serum total protein, albumin, globulin, and triglyceride content and albumin to globulin ratio (P<0.05). Coccidial infection lowered the content of aspartate transaminase and alkaline phosphatase (P<0.01). Coccidial infection lowered digestibility of gross energy, crude protein and crude fat (P<0.1). Dietary addition of YC decreased the OPG in feces on 9th d postinfection. Trial 3 was conducted to investigate the effects of dietary YC on growth performance and immune function of broilers under LPS-induced stress. Three hundreds and sixty 1-day-old AA male broilers were randomly allotted to 3×2 factoral arrangement with 3 YC supplementation levels (0,0.25% and 0.50%) and 2 types of stress (saline and LPS-induced stress). Half of birds were selected for stress challenge, and were intraperitoneally injected with LPS from E. coli at 0.25 mg /kg weight on d 23, 25 and 27 and with Sephadex at 250 mg/kg weight on d 24 and 26. LPS injection lowered the growth performance of birds (d 21~28, P=0.02). ADG of broilers was increased on d 21~28 (P=0.08). Dietary YC increased the content of intestinal sIgA, amount of sIgA+ plasmacytes and intraepithelial lymphocytes (P<0.01). Supplemental YC in broiler diets increased the content of serum IgM, IgG and lysozyme (P<0.05), and lowered the content of ceruloplasmin on 6th d after first LPS injection (P<0.01). Trial 4 was conducted to investigate the effects of YC in broiler diets on the amount and specie of intestinal microorganism using microbe dilution plate techniques and PCR-DGGE of 16S rDNA, respectively. Dietary YC did not affect of amount of bifidobacterium, Lactobacillus, E.Colibacillus in ileum and cecum of broilers (P>0.05). Similarity indexes of DNA-DGGE of cecal bacteria between broilers fed YC-treated diets and control diet were 0.31. The above research results indicate that supplementation of appropriate level of YC in broiler diets could modify immunomudulaltory functions of broilers, and increase nutrient digestibility, improve intestinal morphology. YC's modulation to immune function could improve broiler's anti-infection ability,ease stress and improve growth performance. YC's immunomodulatary function to chickens is one of important mode of action in poultry. The optimal supplementation level in broiler diets is 0.25% under normal environment and 0.25%~0.50% under stress challenge based on this study. |
