Effects of Tryptophan, Melatonin and Dark Period on Performance and Bloodparameters of Broiler Chickens in Heat Stress Condition

A total of 130 Arian broiler chicks were used in this study in order to assess the effects of tryptophan, melatonin and dark regimes on the performance and blood parameters of chickens exposed to heat stress. The chicks were allocated to the experimental units in an unbalanced completely randomized design. The treatments were control group, 40 mg of melatonin per kg of diet from 30-40 days of age and 0.04% of tryptophan per kg of diet from 10-40 days of age and dark period from 10-40 days of age. All treatments were daily exposed to heat stress (39±1C°) for 6 hours from 35-40 days of age. Minimal weight gain was achieved in the third weeks of age and the birds that received tryptophan treatment have highest weight in fourth weeks of weights (P<0.05). The highest level of high density lipo-protein related to tryptophan and melatonin treatments at 40 days (P<0.05). The level of T3 in darkness treatment at 35 days and TBARS level in darkenss and melatonin treatments were decreased (P<0.05). Results of this experiment showed that melatonin supplementation however of its usage after 30 days but had better influence in performance and blood parameters such as increased levels of high density lipoprotein protein and lower of thiobarbituric acid.