| In this dissertation,feeding trials were conducted to evaluate effects of supplementations of dietary tributyrin and Bacillus coagulans on growth performance,pH in digestive tract,specific activity of digestive enzymes,hepatic antioxidant indices,expressions of immune regulatory genes and intestinal morphology of hybrid grouper juveniles.The main contents and results were presented as followed:1.Effects of dietary Bacillus coagulans on digestive enzyme activities,oxidation resistance and expressions of immune regulatory genes of hybrid grouper(male Epinephelus lanceolatus × female E.fuscoguttatus)juveniles.An 8-week feeding trial was conducted to evaluate the influences of dietary probiotics Bacillus coagulans(BC),on growth performance,intestine digestive enzyme activities,oxidation resistance and expression of genes involved in the immune system of hybrid grouper(male Epinephelus lanceolatus x female E.fuscoguttatus)juveniles.Four isoenergetic(340 kcal per 100 g dry matter),isoproteic(53.5%of dry matter)and isolipidic(8%of dry matter)experimental diets were formulated to contain different BC concentrations of 0,0.2×106,2×106,and 20×106 cfu · g-1,and these experimental diets were designated BCO,BC0.2,BC2 and BC20,respectively.To evaluate antioxidant activity and immune system of hybrid grouper,juveniles were exposed to a challenge of 4.5 mg Cu2+/L water for 48 h after feeding trial.Weight gain percentage(WG%)showed no significant differences(P>0.05)among experimental groups.Feed conversion ratio(FCR)of fish fed BC20 was significantly(P<0.05)higher than that of fish fed BC0,BC0.2 or BC2.Fish fed BC20 had significantly lower protein efficiency ratio(PER)than control fish(BC0)and also compared to fish fed BC 0.2 or BC2.Intestinal a-Amylase specific activity was significantly increased in fish fed BC0.2 or BC2(but not in the BC20 group)compared to the BC0 group.Fish fed BC2 had significantly higher hepatic superoxide dismutase(SOD)specific activity than fish fed other experimental diets,and fish fed BC0 had the lowest SOD specific activity among all experimental treatments.Hepatic malondialdehyde(MDA)levels were significantly lower in all BC treatment groups compared to the BC0 control and fish fed BC0.2 and BC2 had lower MDA levels in the liver than fish fed BC20.Fish fed BC0.2,BC2 or BC20 had higher glutathione peroxidase(GPx)specific activity than the control,and highest GPx activity was recorded in the BC2 group.Relative mRNA expression levels of interleukin(IL-8),tumor necrosis factor-alpha(TNF-a)and toll-like receptor(TLR2)genes in the head kidney of fish fed BC2 were higher than those of fish fed other experimental diets.After exposure to a challenge of 4.5 mg Cu2+·L-1 water for 48 h,all groups fed BC-supplemented diets(BC0.2,BC2,BC20)showed higher survival compared to the control.Taken all results into account it appears that,the Bacillus coagulans supplementation at 2×106 cfu · g-1 to the diets improved the intestinal digestive enzyme activities,hepatic oxidation resistance and expressions of immune regulatory genes in the head kidney of hybrid grouper juveniles.2.Effects of dietary tributyrin and mixture of tributyrin and BC on growth,gastrointestinal digestive enzyme activity,pH value,intestinal flora,intestinal biology,and hepatic antioxidant activity of juvenile hybrid grouper.A 9-week feeding trial was conducted to evaluate effects of dietary tributyrin and mixture of tributyrin and BC on growth,gastrointestinal digestive enzyme activity,pH value,intestinal flora,intestinal biology,and hepatic antioxidant activity of juvenile hybrid grouper.At two BC concentrations(0,2×106 cfu/g),five graded levels(0%,0.05%,0.1%,0.2%,0.4%)of tributyrin were designed.Ten kinds of experimental diets were formulated.The experimental results showed that weight gain percentage(WG%)of grouper was significantly influenced by dietary tributyrin levels.WG%,DFI as well as DPI of fish fed TB0.05,TB0.1 were significantly higher than those of fish fed TB0,TB0.2 and TB0.4.No significant differences in FCR and PCR were observed among fish fed different concentrations of dietary tributyrin.Besides,protein efficiency ratio(PER)and FCR of fish fed BC2 were significantly higher compared to those of fish fed BC0.All indices of growth performance except survival were significantly interacted by dietary tributyrin and Bacillus coagulans.Dietary BC significantly decreased pH value in contents extracted from digestive tract after fish was fed for 2 hours,while no differences concerning effects of dietary BC of pH value of intestinal contents were observed after fish was fed for 6 hours.Dietary tributyrin decreased pH value of contents extracted from stomach and intestine when was fed for 2 or 6 hours.Specific activity of gastric pepsin and lipase was not significantly related with concentrations of tributyrin,while gastric a-amylase and intestinal trypsin as well as intestinal lipase specific activities of fish fed 0.05%,0.1%TB were significantly higher than fish fed levels of TB.Besides,specific activities of almost all digestive enzyme in fish fed BC,except for gastric pepsin,were significantly higher than fish fed no BC.Hepatic catalase(CAT)and glutathione peroxidases(GPx)specific activities were increased as dietary TB increased,and thereafter decreased as dietary tributyrin continued to increase.Fish fed BC2 had significantly higher specific activity of CAT and GPx and lower levels of MDA than fish fed BC0.For gut morphology,the microvilli height(Microvillus height,hMV)of midgut was not significantly correlated with levels of dietary tributyrin.Fish fed TB0.05 had significantly higher hMV of foregut and hindgut,fold height(hF)and enterocyte height(hE)of whole gut than fish fed the control diet.Generally,supplementations of 0.05%-0.1%TB and 2×106 cfu/g BC to diets can improve growth performance,activities of digestive enzymes,hepatic antioxidant indices gut morphology of juvenile hybrid grouper. |
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