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.