The effects of neonatal/juvenile heat stress and varying L- tryptophan levels on growth parameters, meat quality, and brain neurotransmitter levels in turkeys
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A 2 x 2 x 4 factorial experiment utilizing 640 male Large White turkeys was conducted to determine the effects of neonatal/juvenile heat stress and tryptophan supplementation upon growth to 129 days of age, as well as meat quality and brain neurotransmitter levels. Treatments consisted of neonatal heat stress (36 continuous hours at 38 C) starting at 5 days of age, juvenile heat stress (8 hours a day at 38 C for 5 consecutive days) starting at 106 days of age, and tryptophan supplementation (0, .1, .2, and .3 % added to the diet) from 112 days of age to market (129 or 138 days of age). Feed consumption, weight gain, and mortality were l recorded and selected meat quality measurements and brain neurotransmitter levels were determined. Weight gain and feed consumption were significantly reduced by juvenile heat stress treatment while early stress, late stress (EL) treatment significantly increased mortality as compared to CC treatment during this period. Such findings revealed that neonatal heat stress did not reduce losses due to heat stress at market age. After live haul, (129 days of age), EC birds had significantly greater cooking loss as compared to birds of the other three treatments and CC birds had significantly larger thigh weights than EL treated birds. In birds analyzed at 138 days of age, CL treatment resulted in a significantly higher Hunter L-value (lightness) in pectoralis major tissue as compared to CC treatment, indicating a darkening of pectoralis musculature due to juvenile heat stress treatment. Tryptophan supplementation resulted in no significant differences in food intake, body weight, or body weight gain. Serotonin, 5 hydroxyindole acetic acid (5-HIAA), and norepinephrine levels increased linearly with dietary tryptophan supplementation in the four brain regions analyzed while linear increases in L-dihydroxyphenylalanine (LÂ·DOPA) occurred in all regions analyzed except for the cerebellum due to Lâ tryptophan supplementation. Plasma levels of serotonin also increased in a positive dose-response fashion while tryptophan supplementation at all levels significantly reduced norepinephrine levels as compared to the basal diet. The addition of .1% tryptophan to the tinisher diet significantly increased carcass weight and thigh weights while no significant differences occurred in breast protein and ether extract, or in either pectoralis major and biceps femoris shear or Hunter color values due to supplemental tryptophan.
- Masters Theses