| Three trials were conducted to determine the effect of different immune stress on growth performance, nutrient metabolism, serum biochemical parameters, meat quality, immunity and cecal microflora in broiler chickens. Five hundred and forty Cobb500 broilers aged 1 day were randomly assigned to 5 groups with 9 replicates per group and 12 birds each replicate (Group 1: control group without experimental stress, Group 2: stress from simplified vaccination, Group 3: stress from general vaccination, Group 4: stress from LPS injection and general vaccination, Group 5: stress from CPM injection and general vaccination).Trial 1 was to evaluate on the effects of different immune stress on growth performance, nutrient metabolism, serum biochemical parameters, and meat quality in broilers. The results showed that feed conversion ratio and apparent digestibility of energy had no significant difference among 5 groups (P>0.05). Average body weight, apparent digestibility of dry matter and crude fat decreased significantly after treatment with LPS and CPM (P<0.05). Apparent ileal digestibility of crude protein of group 5 was lower than the control group (P<0.05), however, the drip loss of group 5 was higher than the control group (P<0.01). The apparent digestibility of crude protein increased in group 2, 3 and 5 (P<0.05). These data suggest that there were no adverse effects on growth performance of broilers without vaccination in the conditions of controlling rational feeding environment. However, excessive immune stress goes against the apparent digestibility of DM, EE, CP and the growth performance of broilers.Trial 2 aimed to study the effects of different immune stress on immunity and immunological parameters in boilers. The results showed that compared with group 1, the levels of secreted IgA decreased significantly after treated with LPS and CPM on 42 days (P<0.01). The spleen index, proliferation of B Lymphocyte, levels of 42 days'serum IgG and titers of 26 days'ND antibody of group 4 were higher than the control group (P<0.05), furthermore, the index of bursa of fabricius of group 5 was lower than the control group (P<0.01). There were no significant difference on the amount of leukocyte and lymphocyte cell, the granulocyte to lymphocyte ratio in blood and the serum lysozyme activity among 5 groups (P>0.05). In conclusion, Immune stress had adverse effects on mucosal immune function of broilers. Experimental model of immune stress was established, however, experimental model of immunosuppression failed to decrease humoral immune response.Trial 3 was conducted to investigate the effects of different immune stress on cecal microflora in broilers. The results showed: the DNA fingerprinting of ERIC-PCR had high stability and good repetition. The molecular weights of gene fragment were almost 500 to 3000bp after ERIC-PCR amplification. The genetic similarity within bacterial populations in group 4 was higher than group 5 on 21 days. However, group 4 had lower genetic similarity with bacterial populations than group 5 on 42 days. Group 3, 4 and 5 had lower cecal digestibility of crude protein than the control group (P<0.01). In conclusion: Different immune stress influenced the structure of cecal bacterial. The DNA fingerprinting of ERIC-PCR reflects intestinal health and status of immune activation. The apparent digestibility of crude protein shows great variabilities in condition of immune stress.All the analysis shows that broilers with simplified vaccination or without vaccination can reach the same growth performance as broilers with general vaccination in the conditions of controlling rational feeding environment, while immune stress can break the homeostasis of cecal microflora structure, impair intestinal mucosal immune function, decrease humoral, cellular immune responses, result lower feed intake and body weight, finally inhibit growth of broiler chickens.
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