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 signiticantly 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 (L·DOPA) occurred in all regions analyzed except for
the cerebellum due to L—tryptophan supplementation. Plasma levels of serotonin also
increased in a positive dose—response fashion while tryptophan supplementation at all levels
signiticantly reduced norepinephrine levels as compared to the basal diet. The addition of
.1% tryptophan to the tinisher diet signiticantly 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.
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