RESUMO
Two experiments were conducted to compare the immunocompetence of Cobb high performance and rustic Label Rouge broilers and the influence of reduced growth rates subsequent to feed restriction on the IgY anti-bovine serum albumin (BSA) response. In the first experiment (EXP), 360 broilers were assigned to 36 cages from 1 to 42 days of age. A completely randomized design was applied in a 3 × 2 factorial arrangement, with 3 groups (Label Rouge, Cobb ad libitum, and Cobb Restricted Intake), and 2 levels of energy (3,100 and 2,800 kcal/kg); there were 6 replicates per treatment. In the second EXP, 384 Cobb 500 male broilers were randomly assigned to the following feed restriction programs from day 8 to 16: Control, fed ad libitum; Quantitative (80% of the control amount); By Time (fed for 8 h/d), and Qualitative (80% limiting nutrients) restriction. Blood samples were collected on days 35 and 42 (EXP 1) and weekly from day 7 to 42 (EXP 2) for IgY anti-BSA quantification. In EXP 1, the production of IgY anti-BSA was lower in the Cobb groups (P < 0.0001) than in the Label Rouge group, and higher in the Cobb Restricted Intake group (P < 0.0001) compared with the same genetic strain fed ad libitum. Birds fed the low energy diet presented lower (P ≤ 0.06) IgY anti-BSA, independent of genetics. In EXP 2, no difference (P > 0.05) was observed 1 wk after the first BSA inoculation. However, at day 28, birds in all feed restriction programs had higher (P < 0.05) IgY anti-BSA than the Control group fed ad libitum. At day 35, the greatest residual effect of IgY anti-BSA was observed in the Quantitative restriction group. No differences (P > 0.05) were observed between groups after 42 d. The 3 early feed restriction programs had beneficial effects on the humoral immune response. Overall, Quantitative restriction promoted a longer lasting IgY anti-BSA response. Lower growth rate, due to feed restriction or genetic potential, improves humoral immunity in broiler chickens.