CRUDE PROTEIN AND SUPPLEMENTAL DIETARY TRYPTOPHAN EFFECTS ON GROWTH AND TISSUE NEUROTRANSMITTER LEVELS IN THE BROILER CHICKEN

Indian River male broiler chickens growing from 7 to 28 d of age were fed on diets containing 120, 210 and 300 g crude protein/kg diet and 0 , 1.67 or 16.7 g added tryptophan (TRP)/kg diet. The hypothesis tested was that crude protein levels and TRP would affect both growth and ne urotransmitter metabolism. Heart, brain and pancreatic neurotransmitte r (noradrenaline (NA), dopamine (DA), serotonin (5-HT) and 5-hydroxy-i ndole-3-acetic acid (5-HIAA)) concentrations were determined by HPLC s eparation and electrochemical detection. Malate dehydrogenase (2-oxogl utarate decarboxylating) (NADP+) (MDH(NADP+); EC 1.1.1.40), isocitrate dehydrogenase (NADP+) ICD(NADP+); EC1.1.1.42) and aspartate aminotran sferase (AAT; EC2.6.1.1) activities were also measured. Supplemental T RP decreased growth and feed intake, Increasing dietary crude protein decreased MDH(NADP+), but increased (ICD(NADP+) and AAT activities. Ad ditional dietary TRP decreased MDH(NADP+) activity, but had no effect on other enzyme activities. Cardiac NA concentrations were directly re lated to dietary crude protein levels while pancreatic levels were inv ersely related. An increase in dietary crude protein decreased both br ain NA and DA. Supplemental dietary TRP increased both 5-HIAA and 5-HT . Changes in feed intake caused by different levels of both dietary cr ude protein and TRP are accompanied;by altered levels of neurotransmit ters. The present study indicates that much larger amounts of TRP are required to make simultaneous changes in feed intake and neurotransmit ters.