Exposure of broiler cockerels to between 35.0 to 37.8 C for 24 hr at 5 days of age increases
their survival when exposed to a heat challenge at 6 weeks of age (35.0-37.8 C; RH 50%
). This'
phenomenon does not resemble acclimation since the physiological changes known to occur in
acclimated birds exposed to heat have not been observed in the neonatally stressed birds.
A series of experiments were conducted to elucidate the mechanisms of neonatally induced
thennotolerance. In Experiment 1, the erythrocyte protein proftle of control and 5 days heated
birds prior to and during exposure to acute heat were detennined. Prior to juvenile heat exposure
no differences in the erythrocytic protein profile of neonatally stressed and control birds were
observed at any age (10, 17, 24, 31 and 38 days of age) when maintained under control conditions.
However, upon exposure to an acute heat challenge (40.5 C; 52 days of age) temporal and
differential expressions of proteins similar in molecular weight to heat shock proteins (HSPs) were
observed between the neonatally stressed and control birds.
In Experiment 2, the effects of neonatal heat stress at various ages (5, 8, 12, 16 days of age) on the
protein synthesis proftle of heart, brain (telencephalon, diencephalon, brain stem, cerebellum) and
liver tissues during exposure to an acute heat challenge were studied. In addition, body temperature
during neonatal heat exposure was monitored. A significant increase in body temperature was
observed during neonatal heat stress. A steady increase in the magnitude of the temperature change
was noticed up to 12 days of age. Body temperature of birds exposed to neonatal heat at 16 days
of age was similar to that of birds heated at 5 days of age.
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