| Three experiments were conducted to investigate systematically the effect of different sources and levels of zinc supplementations basic on corn-soybean diet on the performance, immunocharacterization, tissue zinc deposition, and expression of metallothionein (MT) and fatty acid synthase (FAS) gene of Gushi chick and AA broiler, which possess significant differences in the genetic background. Thus, the zinc requirements of Gushi chick and AA broiler and the bioavailability of different zinc sources can be evaluated better.In the first experiment,400one-day old male Gushi chicken and an equal number of AA broiler were randomly assigned to10groups respectively, and dieted a total of42days with basal ration that added three source of zinc (ZnSO4·H2O, ZnO and ZnAA) and4levels of each zinc(0,30,60and120mg/kg zinc), the performance, immune function, tissue zinc deposition, zinc enzymes activity and MT gene expression were detected, so that to study the suitable zinc requirements of two varieties of chicken, and the effect of different sources of zinc relative Bioavailability and apparent deposition rate on Gushi and AA broilers. The results showed that:(1) Gushi broilers appeared lower sensitivity of dietary additive zinc than AA broilers, Gushi broilers added60mg/kg zinc can meet optimal growth and immunity, the requirements for AA broilers120mg/kg.(2) The concentrations of zinc and MT, and MT mRNA expression levels in liver increased linearly response to the concentration of zinc added, and can be used to evaluate appropriately the relative bioavailability of zinc source. Comprehensive evaluation of all indexes, the bioavailability and the apparent deposition rate of ZnAA and ZnSO4·H2O were not significantly different, but both them were better than ZnO; it displayed similar bioavailability of zinc between Gushi and AA broiler chickens when the rations were supplemented the same zinc density and zinc origin.(3) In different broilers growth period, the apparent availability of zinc were notablely different,2to3weeks old broilers’were significantly higher than4to6 weeks ones, during the entire test period, more than85%dietary zinc was excreted into the environment.In the second experiment,400one-day old male Gushi chicken and AA broiler were divided randomly into10groups, fed2,3,4,5and6weeks with the rations that supplemented500U/kg of microbial phytase basic on experiment-one’s diets, to study the influence of microbial phytase supplementation on broiler performance, tissue zinc concentration and zinc concentration in feces. The results indicated that:(1) microbial phytase increased significantly daily weight gain of Gushi chickens and AA broiler(P <0.01), had no effect on feed efficiency; Phytase×variety interaction showed that phytase raised a higher body weight gain in AA broilers than in Gushi chicken.(2) phytase improved significantly liver and tibia zinc concentration of two varieties of chicken (P <0.01), phytase×zinc level interaction analysis showed that tissue zinc concentrations of control group and30mg/kg of zinc group were higher than other two levels of zinc added processing; phytase didn’t affect the zinc metabolism of organic and inorganic sources (P>0.05).(3) of dietary phytase, the zinc concentration in feces of Gushi chickens and AA broiler decreased20.37%.In the third test,400one-day old male Gushi chicken and AA broiler were use to research the effect of different broilers varieties on abdominal fat deposition under the same nutrition level, and investigated effect of zinc sources and levels on liver FAS mRNA amount. The diets treatment and zinc added were the same as experiment one, the livers were selected on2,3,4,5,6weeks old chickens, and stored in-80℃refrigerator temperature after immediately frozen in liquid nitrogen transferred12hours. The results proclaimed:(1) the percentage of abdominal fat of3-week and6-week old Gushi chickens were strikingly lower than AA broiler (P<0.01), as the age increased, the percentage of abdominal fat of the two varieties of chicken increased markedly (P<0.01). liver FAS mRNA levels showed similar regularity, AA broiler was significantly higher than that of Gushi chicken with the same weeks of age, compared with that of the same weight but different ages, the liver FAS mRNA levels of3-week old Gushi chicken was significantly lower than that of2-week old AA broiler.(2) dietary zinc levels above60mg/kg, the percentage of broiler abdominal fat significantly reduced (P<0.05);60and120mg/kg feed zinc levels inhibited the expression of FAS mRNA in liver,and had nothing to do with zinc source. In summary, the liver zinc concentration and MT mRNA levels were sensitive indicators to assess relative bioavailability of zinc source. different varieties of broilers displayed different requirements for zinc, Gushi chickens could gain optimization performances with95.53mg/kg of total dietary zinc, while that of AA broiler is higher than Gushi chicken; the apparent bioavailability of feed grade ZnAA and ZnSO4·H2O had no significant difference, but were significantly higher than ZnO; rations added microbial phytase could improve the rate of zinc metabolism and reduce the pollution of heavy metals on the ecological environment; the intensity of fat metabolism were remarkably different on different growth rate of broilers. The achievements of this research possessed positive significance to the development of scientific research and industrialization for country high-quality chickens. |
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