| Six experiments were conducted to study the effects of dietary supplemental zinc amino acid complex during whole life stage on the performance, immune responses and tissues antioxidant capacity of hen at different physilogical stage. Possible mechanisms of ZnAA regulating immunity were disclosed by probing the relative zinc bioavailability, the change of tissue zinc dynamics during the immune reaction and gene expression of functional protein at transcriptional level. The effects of different application regimes of ZnAA on the immune responses and antioxidant capacity were also examined in the current study.In the experiment 1 and 2, the effects of consecutive supplementation of ZnAA on the performance, immune reaponses and antioxidant capacity of pullet and laying hens fed with corn-soybean meal diet were examined respectively. Compared to ZnSO4 dietary supplementation of ZnAA increased the relative weight of spleen at age of pullet hens (P < 0.05) , enhanced the proliferation response of peripheral blood lymphocyte to ConA at age of 8 and 18 wk , and to LPS at age of 18 wk (P < 0.05) , elevated the activities of T-SOD and CuZn-SOD in hepatic tissues at age of 8 wk , the TAOC of hepatic tissues at age of 8 and 18 wk (P < 0.05) , decreased the production of MDA in livers at age of 18 wk (P < 0.05), elevated the activities of T-SOD and CuZn-SOD in splenic tissues at age of 18 wk , and the TAOC in splenic tissues at age of 8 wk (P < 0.05) , reduced the content of MDA in splenic tissues at age of 8 and 18 wk (P < 0.05) . During laying stage, the decreased mortality and percentage of cracked egg, increased egg production, prolonged storage time of eggs were observed in layers supplemented with ZnAA (P < 0.05) . In addition, supplemental ZnAA could enhance the proliferation response of lymphocyte to ConA and LPS, increase BSA antibody titer on day 7 post the primary inoculation and 10 day post the second inoculation, elevate the activities of antioxidant enzymes and proteins in hepatic and splenic tisuues, and reduce the production of MDA in tissues (P<0.05) .The effects of additional either sulphate Zn/Cu/Mn or Availa-Zn/Cu/Mn based on practical level on the performance, immune responses and antioxidant capacity of bird were also examined in experiment 1 and 2. Increase of the level of Zn/Cu/Mn from Availa-Zn/Cu/Mn based on practical level improved development of thymus, increased the livability, improved egg quality, enhanced proliferation of blood lymphocyte to ConA or LPS, increased antibody response to BSA in laying stage, elevated activities of antioxidant enzymes and TAOC, reduced the production of MDA in hepatic or splenic tissues, but addition of the same level of Zn/Cu/Mn from sulphate Zn/Cu/Mn had no effect on the examined index except elvation of the hepatic TAOC at age of 18 wk . Partial replacement of supplemental sulphate Zn/Cu/Mn in practical diet with Availa-Zn/Cu/Mn could also increase the relative weight of thymus at age of 18 wk , enhance the cellular-mediated immunity andelevate the antioxidant capacity of hepatic tissues.Experiment 3 was conducted to investigate the effects of level and source of supplemental zinc on the growth, zinc-metalloenzymes, tissue zinc deposition, zinc excretion and retention of broiler chicks. Zinc concentration of serum and tibia, fecal zinc excretion were increased with the increase of level of supplemental zinc. Compared to ZnSO4 (P<0.05), dietary supplementation of ZnAA increased the zinc concentration in tibia and zinc retention, and reduced zinc excretion (P<0.05). The RBV of ZnAA relative to ZnSO4was 135.1%, 127.1%, 111.5% based on serum zinc concentration, tibia zinc concentration and zinc retention, respectively.Experiment 4 was conducted to study the effects of zinc source and level on the performance, eggshell quality, antibody response of BSA, tissues zinc concentration and activity of some zinc-dependent enzymes of laying hens. Compared to ZnSO4, ZnAA tended to enhance immunity and increase the livability, increase egg shell strength and... |
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