| Some studies have demonstrated that the effect of zinc-bearing zeolite clinoptilolite (ZnZC) in replacement of antibiotics on growth performance of broilers, but there is neither enough data about the effects of ZnZC in replacement of inorganic zinc (ZnSO4) in diets on zinc transport in intestine of broiler chicks, nor study on the protection of ZnZC on intestinal function. Therefore, this study was conducted to investigate the preparation of ZnZC with liquid ion exchange method, evaluate zinc desorption and adherence of bacteria in vitro, investigate zinc bioavailability from ZnZC and its transport mechanism in intestine of broilers, and to evaluate the effects of ZnZC as zinc supplements or alternatives to antibiotics on intestinal function of broiler chicks, as well as the regulatory effect of ZnZC on intestinal barrier of broiler chickens infected with Escherichia coli lipopolysaccharide (LPS) and its possible mechanism. This study may provide the theoretical basis of the application of ZnZC in poultry. The study was divided into the following five sections:Trial 1 was conducted to investigate the preparation of ZnZC with liquid ion exchange method, the adsorption of ZnZC on E. coli and S. enter itidis, and zinc desorption from ZnZC. The optimum preparation conditions of ZnZC were 2.5 mol/L Zn concentration, pH 4.5, temperature 70 ℃, and time 4 h. The zinc loading of zeolite clinoptilolite was 1.55%. The factors affecting the zeolite adsorption of Zn2+ was temperature>zinc ion concentration> pH> time. The adsorptions of ZnZC on E. coli 249 and S. enteritidis 13076 were superior to zeolite clinoptilolite, and when the addition dose was above 25 mg/mL, the adsorption capacity was more obvious. Zn2+ could be controlled-releasing from ZnZC and reached the desorption equilibrium in 60 min, which was affected by pH and ion species.Trial 2 was conducted to explore the possibility of ZnZC as a zinc supplementation and investigate the effect of ZnZC on growth performance, serum parameters, organ weights, trace element content and zinc bioavailability in broilers. A total of 360 one-day-old Arbor Acres (AA) broiler chickens were randomly divided into 6 groups with 6 replicates of 10 birds for a 21-d feeding period. Dietary treatments included a corn-soybean meal diet (29.1 mg of Zn per kg of diet) without supplemental zinc (control) and control diet supplemented with 20,40,80,120 mg/kg zinc (ZnZC) or 80 mg/kg zinc (ZnSO4), respectively. The feed: gain ratio was improved (linear, P=0.003) by the addition of ZnZC during 1-21 d. ZnZC supplementation increased the absolute weights of pancreas (linear, P=0.042) and tibia (linear, P=0.048) on d 21, decreased the content of TC (linear, P=0.023) and TG (linear, P=0.016) and increased the GLU concertation (linear, P=0.001) in serum on d 21. ZnZC treatment increased zinc content in whole blood (linear, P=0.003), liver (linear, P<0.001; quadratic, P<0.001) and tibia (linear, P<0.001) on d 14, and in liver (linear, P=0.001) and tibia (linear,.P<0.001) on d 21, but did not affect the deposition and excretion of Cu, Mn, Fe or Ca (P>0.05). Supplementation of 120 mg/kg zinc from ZnZC improved Ca contents in whole blood (linear, P=0.002) and breast muscle (linear, P=0.006) on d 14. Using multiple regression slope ratio with ZnSO4 set at 100%, the relative bioavailability values (RBV) of ZnZC were 129%(P>0.05) and 149%(P<0.05), respectively, based on tibia zinc on d 14 or d 21; and the RBV of ZnZC were 113%(P>0.05) and 115%(P>0.05) based on liver zinc on d 14 or d 21, respectively.Trial 3 was conducted to determine the effect of ZnZC in replacement of ZnSO4 on growth performance, nutrient retention, digestive enzyme activities, intestinal function and mRNA expression of zinc transporters in broiler chickens. A total of 180 one-day-old Arbor Acres chickens were randomly divided into 3 groups with 6 replicates of 10 birds for a 21-d feeding period. Birds were fed a basal corn-soybean meal diet (29.1 mg of Zn per kg of diet) without supplemental zinc (control) or the same diet supplemented with 80 mg/kg zinc from ZnSO4 or ZnZC. ZnZC and ZnSO4 treatment had lower feed:gain ratio than control group (P<0.05). Addition of ZnZC increased the apparent retention of organic matter (P<0.05) and ether extract (P<0.05) during 14-17 d, and increased pancreatic lipase activity at 14 (P<0.05) and 21 d (P<0.05) as well as amylase activity at 21 d (P<0.05). Addition of ZnZC increased the villus heights and villus height to crypt depth ratio at duodenal (P< 0.05) and jejunal (P <0.05) segment of broilers at 14 d. Broilers fed the diet supplemented with 80 mg/kg Zn from ZnZC had higher villus heights and villus height to crypt depth ratio of duodenum (P<0.05) and jejunum (P<0.05) than those fed control diet on d 21. ZnZC treatment increased (P<0.05) IgG and slgA concentrations in jejunum at 21 d. Metallothionein (MT) mRNA levels in the duodenum of chicks fed the diet with 80 mg/kg zinc from ZnSO4 or ZnZC were higher (P<0.05) than that in the control group. The mRNA levels of zinc transporter 2 (ZnT-2) and 5 (ZnT-5) in the duodenum of chicks fed the diet with 80 mg/kg zinc from ZnZC were similar to those of the control, but both were lower(P< 0.05) than those of chicks fed ZnSO4 diet. Compared to control group, addition of ZnZC did not affect the mRNA expression of zinc transporters in jejunum, but ZnT-2 (P< 0.05) and MT (P<0.05) mRNA levels in jejunum of broilers fed ZnZC were lower than those in ZnSO4 group.Trial 4 was conducted to evaluate the effect of ZnZC in replacement of antibiotics on growth performance, cecal microflora, immune organ index, serum antioxidant paramenters, intestinal antioxidant function and status, immune function of broiler chickens. Birds were fed a basal corn-soybean meal diet (including ZnSO4) (control) or the same diet supplemented with15.5,31.0,62.0 mg/kg ZnZC (based on zinc content, the addition of ZnZC was 0.1%,0.2%,0.4%, respectively) or 40 mg/kg chlortetracycline (ANT). ZnZC treatment had positive effect on average daily gain (ADG) (linear,.P=0.005; quadratic, P=0.093) of broilers during 1-21 d, better than that of ANT. Supplementation with ZnZC decreased the population of Escherichia coli in cecal content (linear, P=0.048; quadratic P=0.045) on d 21 and d 42 (linear, P=0.032; quadratic, P=0.081), increased 21 d thymus index (linear,P<0.001),42 d spleen index (linear,P=0.051) and bursa index (linear, P=0.083), improved serum T-SOD (P<0.05), Cu-Zn SOD (P<0.05) and T-AOC (P<0.05) on d 21 and d 42, reduced MDA content in serum on d 42 (linear,P=0.004). The activities of T-SOD (linear, P=0.001), Cu-Zn SOD (linear, P<0.001) and T-AOC (linear, P<0.001) in jejunal mucosa were increased by supplementary ZnZC on d 21. MDA contents in jejunum (linear, P=0.001; quadratic, P=0.008) and ileum (linear, P=0.018; quadratic, P=0.012) were reduced by ZnZC treatment on d 21. GSH content in jejunum was increased on d 21 (linear, P<0.001; quadratic, P=0.009) by ZnZC treatment. Compared to control and ANT,31.0 or 62.0 mg/kg ZnZCincreased IgG in jejunal mucosa at 21 d (P<0.05), and 15.5 mg/kg ZnZC supplementation improved slgA content in jejunum at 42 d (P<0.05).Trial 5 was conducted to evaluate the effect of ZnZC on antioxidant function, TLR-MyD88 signaling pathway, I-κBα and NF-κB expressions in intestinal barrier of broiler chickens infected with E coli LPS, to clarify the mechanism of ZnZC protecting the intestinal barrier from stress. A 2×2 factorial arrangement containing 240 broilers of four treatments was used in which diets (basal diet+80 mg/kg zinc from ZnSO4 or ZnZC) and LPS/NaCl treatment. Half birds from each treatment were challenged with 0.9% NaCl solution or LPS (500 μg/kg body weight) intraperitoneally in the lower abdominal region at 16,18 and 20 d of age. The basal diet was same to trial 2. LPS stress led to decrease (P<0.05) the activities of T-SOD, Cu-Zn SOD and GSH-Px, the expreesion of GSH-Px mRNA and GSH content in jejunal mucosa of broilers fed ZnSO4 diet, but did not affect (P>0.05) those index except T-SOD of broilers fed ZnZC diet. LPS stress increased (P<0.05) the contents of MDA and NO, as same as i-NOS activity and the expreesion of TLR4 mRNA (P<0.05) in jejunal mucosa of broilers fed ZnSO4 diet, but did not affect NO content or expreesion of TLR4 mRNA (P>0.05) in jejunal mucosa of broilers fed ZnZC diet. Addition of ZnZC improved A20 mRNA expression in jejunal mucosa (P<0.05). LPS treatment improved the expression level of NF-κB p65 in jejunal mucosa of broilers fed ZnSO4 diet, did not affect that (P>0.05) fed ZnZC diet. Under LPS stress, IκB-α expression level in broilers fed ZnZC diet was higher than that fed ZnSO4 diet(P<0.05).Based on those results, it can be concluded as follows:(1) The optimum preparation conditions of ZnZC were 2.5mol/L Zn2+ concentration, pH 4.5, temperature 70 ℃, and time 4 h. The zinc loading of zeolite clinoptilolite was 1.55%. The adsorptions of ZnZC on E. coli 249 and Salmonella enteritidis 13076 were superior to zeolite clinoptilolite. Zn2+ could be released from ZnZC, affected by pH and ion species(2) ZnZC, which had better bioavailability to ZnSO4, could promote accumulation of trace elements and improve growth performance of broiler chickens.(3) The mRNA expressions of zinc tranporters in intestine between ZnZC group and ZnSO4 group were different, implying that the absorption and transport of zinc from ZnZC may be different with ZnSO4. ZnZC modulated intestinal structure and function, digestive enzyme activities and nutrient retention to improve feed efficiency.(4) Supplementation with 15.5 or 31.0 mg/kg ZnZC (based on zinc content, the addition was 0.1% or 0.2%) modulated microbial populations and improved immune function and antioxidant status in the gastrointestinal tract, which was as efficacious as 40 mg/kg chlortetracycline in enhancing growth performance. ZnZC may be used as a new growth promoter in replacement of antibiotics in poultry feed.(5) LPS stress induced to decrease the antioxidant function in intestine of broiler, and activate TLR signaling pathway, leading to intestinal injury. ZnZC may have positive effect on intestinal mucosa of broilers by improving intestinal antioxidant function and upregulating zinc finger protein A20 mRNA expression to inhibite the expressions of TLR4, NF-百B and NO, which further inhibited TLR4/MyD88/NF-kB/i-NOS/NO singaling pathway. |
PDF Full Text Request