Effects Of Immunological Stress On Endogenous Amino Acids Losses And Requirement For Threonine Of Broilers

Five experiments were conducted to study the effects of immunological stress on the endogenous losses and dietary digestibility of amino acids at the terminal ileum of broilers, as well as the effects of immunological stress and the different dietary ratios of the digestible threonine/lysine on growth performance, hormonal level, carcass traits, protein and lipid metabolism, and the immune function of broilers.Experiment 1, 400 sixteen day-old AA male broilers were randomly assigned into one control and three treatments, with 100 broilers each treatment. Chicks were given i.p. with different dosage (500, 1000 and 1500 ug/kg BW) of LPS in treatments and with sterile saline in control respectively, and injected repeatedly with same dosage on the eighteenth and twentieth day of age. Blood and spleen samples were taken at 2,4,8 and 24 h after the third injection, hormonal levels and immunity were determined. The results were showed as follows: (1) LPS administration increased the serum levels of cortisone at 2, 4, and 8 h post-injection (P<0.01). And the plasma levels of PGE₂ had also the trend to increase (P>0.10). The serum level of T₃ decreased and the ratios of T₄/T₃ increased at 2 and 4 h post-injection (P<0.01), and at 8 h post-injection, these were not significant difference among treatments (P>0.10). But at 24 h post-injection, the levels of T₃ and the ratios of T₄/T₃ showed the opposite change to 2 or 4 h (P<0.01). LPS administration didn't affect serum levels of GH and INS significantly (P>0.10). (2) LPS administration increased the proliferation responses of lymphocyte in blood and spleen to Con A and in blood to PHA (P<0.10), and also increased the percent of CD3 +T and CD4+T and ratios of CD4+T/CD8+T(P<0.10), but it didn't affect NDV HI antibody tiler significantly (P>0.10). (3) LPS administration also promoted the mRNA expression of IL-2 and IFN-γ in spleen (P<0.10).Experiment 2, 300 sixteen day-old AA male broilers were used, 150 were randomly assigned into control, immunological stress and pair-fed treatments to estimate endogenous losses of amino acids at the terminal ileum, the other 150 were also assigned into the same three treatments to determine the dietary digestibility of amino acids, with 5 replications each treatment. On the sixteenth, eighteenth and twentieth day of age, chicks were injected i.p. with 500 ug/kg BW of E.coli LPS in immunological stress and with saline in control and pair-fed treatments respectively. Chicks in control and immunological stress treatments were fed ad libitum, and chicks in pair-fed treatment were fed the same amount of diets with stress treatment within one day before being slaughtered. Amino acids and indicator contents in ileal digesta were determined. The results were showed as follows: (1) Immunological stress increased endogenous losses of amino acid (mg/d) at the terminal ileum of chicks except glycine compared with pair-fed chicks, and eight kinds differed significantly (P<0.10), but the amount of endogenous losses in stress group were lower than that in control group except cystine and histidine, and ten kinds differed significantly (P<0.10) between these two groups. (2) The immunological stress didn't affect the dietary digestibility of amino acids significantly (P>0.10), although there was a increasing trend.Experiment 3, 750 one day-old AA male broilers were assigned into 10 treatments, with 5 replications each treatment. The ratios of the dietary digestible threonine to lysine were 54/100, 61/100, 67/100, 70/100 and 73/100 respectively. On the sixteenth, eigliteenth and twentieth day of age, chicks were injected i.p. with 500 u,g/kg BW of E.coli LPS in stress and with saline in control treatment. On the twenty-first day of age, growth performance, hormonal levels and carcass traits were determined. The results were showed as follows: (1) Immunological stress decreased the feed intake, body weight gain and breast muscle contents and increased the ratio of feed/gain (PO.10), but serum levels of Tiand IGF- I increased after overcoming stress (P<0.10). (2) Following the rising of dietary ratios of threonine/lysine, anabolic hormone increased and carcass traits improved (PO.10). (3) There existed interactions on body gain weight, empty carcass and breast muscle contents between immunological stress and dietary ratios of threonine/lysine (PO.10). (4) Chicks in control treatment required the 64/100 of threonine/lysine to achieve the best body weight gain and FCR, but corresponding ratios were 70/100 and 71/100 for chicks in immunological stress treatment.Experiment 4, 460 fifteen day-old AA male broilers were used. 60 were assigned into control and immunological stress treatments, the additional 400 were arranged randomly into 10 treatments, and five replications each treatment. On the sixteenth, eighteenth and twentieth day of age, chicks were injected i.p. with 500 Mg/kg BW of E.coli LPS in stress treatment and with saline in treatment, the ratios of dietary threonine/lysine were 53/100, 61/100, 66/100, 69/100 and 71/100 respectively. On the twenty-first day of age, body composition and biochemical indexes in serum were determined. The results were showed as follows: (1) Immunological stress accelerated the catabolic metabolism and inhibited the accretion of body protein (PO.10), and decreased the body water contents and increased the lipid contents (PO.10), but it didn't affect the body protein content and serum levels of TC> TG> LDL-C and HDL-C (P>0.10). (2) Increasing the dietary ratios of threonine/lysine promoted the body protein accretion and decreased the body lipid content (PO.10). (3) Immunological stress increased the dietary requirement ratios for threonine/lysine to achieve the maximal body protein accretion. (4) There didn't exist the interaction between the immunological stress and dietary ratio of threonine/lysine for the other determined indexes except the serum levels of uric acid and LDL-C.Experiment 5, 300 one day-old A A male broilers were randomly arranged into 10 treatments, and live replications each treatment. On the sixteenth, eighteenth and twenty-first day of age, chicks were injected i.p. with 500 fig/kg BW of E.coli LPS in stress treatment and with saline in treatment. The dietary ratios of threonine/lysine were 54/100, 60/100, 65/100, 71/100 and 77/100 respectively. On the fifteenth and twenty-sixth day of age, immune organ were weighted, on the twenty-sixth day of age. serum contents of total protein and albumin and antibody titers to SRBC and BSA were determined. Lymphocytes were separated from blood and cultured, and IL-2 contents in culture medium were determined. The results were showed as follows: (1) Immunological stress promoted the development ot bursa and spleen (PO.10), and increased the IL-2 contents in culture medium (PO.10). (2) Increasing the dietary ratios of threonine/ lysine had the same effects on immune organ and IL-2 contents as the immunological stress (PO.10), and it also increased the globulin content and antibody titers to BSA in...