Crude protein and supplemental dietary tryptophan effects on growth and tissue neurotransmitter levels

Indian River male broiler chickens growing from 7 to 28 d of age were fed diets containing 120, 210 and 300 g crude protein and 0, 1.7 or 16.7 g of added tryptophan (TRP)/kg diet. The hypothesis tested was that crude protein levels and TRP would affect both growth and neurotransmitter metabolism. Heart, brain and pancreatic neurotransmitter norepinephrine (NE), dopamine (DA), serotonin 5-HT and 5-hydroxy-indole-3-acetic acid (5-HIAA) concentrations were determined by HPLC separation and electrochemical detection. Cardiac NE concentrations were directly related to dietary crude protein levels while pancreatic levels were inversely related. An increase in dietary crude protein decreased both brain NE and DA. Supplemental dietary TRP increased both 5-HIAA and 5-HT. Changes in feed intake caused by different levels of both dietary crude protein and TRP are accompanied by altered levels of neurotransmitters. The present study indicates that much larger amounts of TRP are required to simultaneously change feed intake and neurotransmitters.