Growth and immunity of broiler chicks as affected by dietary arginine

A dietary deficiency of Arg may suppress chick immune system functions; how ever, research evaluating immune function responsiveness of commercial broi lers fed dietary Arg levels near NRC (1994) recommendations is sparse. Ther efore, three experiments were conducted to evaluate growth and immunity of broilers fed varying Arg levels near NRC (1994) specifications. Because Arg and Lys are similar in structure and are known to compete in intestinal ab sorption, dietary Lys treatments [near NRC (1994) recommendations] were eva luated to determine if Arg and Lys interact to affect broiler immunity. The re were four dietary treatments in Experiment 1 representing a 2 x 2 factor ial design of additional Arg (120% of NRC) or additional Lys (120% of NRC) added to a control diet containing 100% of NRC Arg and Lys (six replication s per treatment). Experiment 2 contained the following four treatments: the control diet; the control diet plus L-Arg (0.20% Arg of diet); the control diet plus L-Lys HC1 (0.20% Lys of diet); and the control diet plus L-Arg-L -Glu (0.10% Arg of diet). Graduations of Arg were fed from 90 to 120% of NR C in 10% increments in Experiment 3. Also, half of the birds were exposed t o vaccinations of Newcastle disease virus and infectious bronchitis virus i n Experiment 3 to derive a 2 x 4 factorial design. Experiments 1 and 2 were conducted from Days 1 to 18 and Experiment 3 was conducted from Days 1 to 15 in Petersime battery brooders. No interactions occurred between dietary Lys and Arg in Experiment 1. Increasing dietary Arg, but not Lys, from 100 to 120% of the NRC recommendation increased (P less than or equal to 0.05) Day 18 BW gain, Treatment differences in the cutaneous basophil hypersensit ivity assay in Experiment I did not occur. In Experiment 2, treatment diffe rences in growth responses, lymphoid organ development, and primary antibod y titers to SRBC did not occur. Unvaccinated birds in Experiment 3 fed an A rg-deficient diet had lower (P less than or equal to 0.05) feed conversion in comparison with vaccinated birds fed an Arg-deficient diet. Vaccinated b irds had lower (P less than or equal to 0.05) Day 15 BW than unvaccinated b irds, but higher (P less than or equal to 0.05) titers to Newcastle disease virus. Increasing dietary Arg in Experiment 3 increased plasma Arg (P less than or equal to 0.05), but did not affect plasma Lys. Although increased dietary Arg improved BW gain in Experiment 1, minimal effects were noted in growth and immune system parameters throughtout this study. A dietary Arg level near the NRC (1994) recommendation should support proper immune syste m functions in healthy chicks.