Effect of supplementary threonine in starter wheat-based diets on growth performance, immune system and intestinal organ parameters of broiler chickens

In order to evaluate effects of supplementation of a low-protein wheat-based diet (WBD) with different levels of threonine on performance and immune function, 280 mail one-day-old broiler chicks (Ross 308) were used in a completely randomized design with seven treatments of four replicates each. Treatments were a WBD supplemented with seven levels of threonine (90, 100, 110, 120, 130, 140, and 150% of NRC (1994) recommendation. During 1-21 d of age, feed intake (FI), body weight gain (BWG) and feed conversion ratio (FCR) were recorded weekly. For humoral immune system evaluation, sheep red blood cells (SRBC) was injected; and in order to evaluate cutaneous basophil hypersensitivity (CBH) response, Phytohemagglutinin (PHA) (100 µg) was injected into toe web. Increasing the threonine level to more than 130% of NRC (1994) recommendations, decreased BWG (P<0.05) during 15 to 21 d of age. Adjusting threonine level at 110% NRC (1994) recommendations comparing to 90%, improved FCR during 15 to 21 and 1 to 21 d of age (P<0.05). Supplementation of the WBD with threonine at the levels of 110, 120, and 130% of NRC (1994) recommendation, significantly increased antibody titre against SRBC (P<0.05). Higher dietary threonine levels (110% and 130% of NRC (1994) recommendations), increased CBH response after PHA injection (P<0.05). Overall, it seems that the requirements of threonine in WBD for optimum performance and immune system enhancement, is more than the NRC (1994) recommendations.