Isoleucine needs of thirty- to forty-day-old female chickens: immunity

Department of Poultry Science, Mississippi State University, Mississippi State, Mississippi 39762-9665, USA.

Broilers fed diets with reduced amino acid levels may be limiting in isoleucine. Because research addressing daily Ile needs for broiler immunity is sparse, Ile responses for immunity in female broilers were evaluated in 2 experiments in broilers from 30 to 42 d of age. Cellular and humoral immunity were evaluated in diets limiting in Ile and diets varying in Ile from deficient to adequate. Pen was the experimental unit in both experiments. Treatments in experiment 1 consisted of 2 levels of Ile (0.42 vs. 0.72% total of diet) and 3 strains of broilers, Arbor Acres+, Ross 508, Ross 708 (6 treatments; 5 pens each). In experiment 1, measurements consisted of: a cutaneous basophil hypersensitivity test to phytohemagglutinin-P (PHA-P) on d 37 and 38; cell quantification of CD4+, CD8+, and BU-1+ lymphocytes at d 41 and 42; and relative immune organ weights at 42 d. No Ile x strain interaction occurred. Feeding an Ile-deficient diet to broilers suppressed the cell mediated response to PHA-P, and reduced thymus weight and the percentage of CD8+ T cells. There were no significant differences between strains. In experiment 2, gradations of Ile (0.42, 0.50, 0.58, 0.66, 0.74, and 0.82% total of diet) were fed to one strain (Ross 508) of female broilers (7 pens per diet). A control diet containing 0.70% Ile (6 pens) was compared with an Ile surfeit concentration. Measurements in experiment 2 consisted of a hypersensitivity test to PHA-P on d 35 and 36; a primary antibody response to SRBC from 35 to 42 d; cell quantification of CD8+ alpha, beta, and T cell receptor (TCR)-1 (delta/gamma) lymphocytes on d 41 and 42; and immune organ weights at 42 d. Immunity measurements in birds fed surfeit Ile in the titration diets were equal to birds fed the control diet. A linear response to increasing Ile was obtained for relative bursa, but no Ile quadratic responses were noted for other measurements in experiment 2. Although feeding broilers a diet deficient in Ile suppressed some immune criteria, it does not appear that a marginal Ile deficiency will compromise immunity in growing female broilers.