Effect of Excess Dietary Tryptophan on Performance, Plasma Hormone Levels and Immune Function of Broiler Chickens Reared Under Hot and Humid Summer Conditions

The effects of L-Tryptophan supplementation on growth performance, hormone levels, and immune function of heat-stressed broiler chickens were investigated. For 42 days, 480 male chicks were exposed to repeated cycles of hot temperatures and fed one of four diets: a basic diet (control group) or the same diet with extra L-Tryptophan added at three different levels (0.2, 0.4, and 0.6 g/kg diet). L-tryptophan supplementation did not significantly improve overall growth performance under heat stress. However, broilers fed 0.2 and 0.6 g/kg L-Tryptophan had a better feed conversion ratio at 10 days old. There were no significant differences in white blood cell counts. Interestingly, L-tryptophan supplementation increased antibody production against Influenza and Newcastle disease viruses at 14 days. Additionally, L-tryptophan influenced hormone levels, slightly decreasing growth hormone and increasing thyroxin at 10 days, with further increases in triiodothyronine observed at 24 and 42 days. While L-tryptophan supplementation did not enhance overall growth performance under heat stress, it positively impacted blood parameters like thyroxin, triiodothyronine, and immune response against specific viruses.