Influence of Various Levels of Energy and Protein on Performance and Humoral Immune Responses in Broiler Chicks

Six hundred and forty day-old broiler chicks (Ross 308) were divided into 80 groups of 8 birds each. A 4x4 factorial arrangement in a complete randomized design experiment was used to study the effect of four levels of energy (2900, 3000, 3100 and 3200 kcal/kg) and four levels of protein (17, 20, 23 and 26%) on performance and humoral immune responses of chickens. Each diet was randomly fed to five groups of chicks from 5 to 35 d of age. Group weight and feed intake were recorded eveiy 5-day. Lymphoid organs and liver weight were determined at 10, 15 and 20 d. Five birds were intramuscularly injected with 1 ml/chick sheep red blood cell (SRBC) 15% suspension in PBS at days 15 (primary injection) and 25 (secondary injection) of age. Blood samples were collected 5 and 10 days after each injection and subsequently were evaluated for total immunoglobulin, IgM and IgG anti-SRBC titers. Chicks BW and FCR improved as dietary energy and protein increased in every period and whole experimental period. The chicks feed intake was not influenced by dietary protein level. Any considerable effects of dietary energy and energy levels on lymphoid organ weights were observed. Broiler fed low levels of protein had heavier liver weight than those fed diets with high levels. Total and IgG anti-SRBC antibody titers were rose in birds fed low energy diets at postprimary injection (PPI) days. Immunoglobulin M titers were not significantly altered by different levels of energy at both PPI and PSI days. Dietary protein contents did not influence birdʹs anti-SRBC antibody titers. Protein and energy of diet are equally important for early growth and feed efficiency. Whereas, there are negative phenotypic contribution between immunocompetence and rapid growth in chickens, rapid growth decreased immune responses. This means that birds were selected for rapid growth but not for enhanced immune responses.