Effects Of Arginine On Growth Performance And Immune Function In Broilers And The Underlying Mechanism

In the present study, five experiments were conducted to investigate the effects of different levels of arginine in diets on growth performance, immune function, nitric oxide content, inducible nitric oxide synthase (iNOS) activity and its gene expression, and amino acid contents in serum and muscle of broilers. In animal experiments,300one-day-old Arbor Acre broilers were chosen and divided into5dietary treatments with6replicates and10chickens per replicate. The broiler chickens in the five treatments were fed with the basal diet supplemented with0(arginine-deficient group),4.5(arginine-normal group, control),9.0,13.5, and18.0g/kg arginine, respectively. The feeding trial lasted42d divided into two stages of d1-21and22-42. Experiment1was conducted to study the effects of different levels of arginine in diets on the growth performance and related incretion indexes in broilers. Experiment2was conducted to determine lymphocyte proliferation, antibody titer of Newcastle disease, immunoglobulin, cytokine, immune organ index and phagocytic index, in order to study the effects of different levels of arginine in diets on immune functions in broilers. Experiment3was conducted to study the effects of different levels of arginine in diets on NO content, iNOS activity and its gene expression, and investigate the molecular mechanism by which arginine affected broiler’s immune function via iNOS-pathway. Experiment4, an in vitro test, was conducted to study the effects of different levels of arginine in medium on lymphocyte immune function and NO production. Experiment5was conducted to study the effects of different levels of arginine in diets on amino acid contents in serum and muscle of broilers. The results showed as follows:(1) With increasing of dietary arginine levels, the average daily gain (ADG) during the entire experiment period was improved linearly or quadratically, and the ratio of feed to gain (F/G) was decreased quadratically. On d21, the contents of insulin (INS) and insulin-like growth factors Ⅰ(IGF-1) in serum of broilers were improved quadratically with increasing of dietary arginine levels.(2) On d21, thymus index, serum immunoglobulin (Ig) A and interleukin-2(IL-2) of broilers were improved quadratically with increasing of dietary arginine levels. On d42, the Newcastle disease (ND) antibody titers, lymphocyte proliferation and IgM were improved quadratically with increasing of dietary arginine levels.(3) With increasing addition of arginine in diets, NO content and iNOS activity in serum as well as iNOS mRNA expression in the ileum and liver of broiler chickens increased quadratically at the age of21d. (4) Arginine in suitable doses to growth and immunity in broilers did not significantly affect the contents of other amino acids in serum and muscle.(5) The results in vitro test showed that the contents of IL-2and iNOS in lymphocyte culture medium increased quadratically with increasing addition of arginine, and80μg/mL arginine supplement group had the highest value.The experimental results suggested that dietary supplementation of arginine exceeding the normal level could further improve ADG and immunity of broilers and the best dosage was0.97%～1.05%which was equivalent to an addition of arginine by0.52%-0.60%in normal diet.