Abstract
SummaryPinealectomized female chickens (PX) were given an acute thermal challenge (60 min at 42°) during two portions of their 12L:12D photoperiod. Five birds from each surgical treatment group, including sham operated (PN) and nonoperated controls (C), were exposed to heat 4 hr after onset of light (photophase) and a like number 4 hr after onset of darkness (scoto-phase). There were no differences in rectal temperature (TT) or respiratory rate (RR) among treatment groups of the photophase heat challenge. Heat exposure during the scotophase caused a significantly greater (P < 0.01) hyperthermia in PX birds after 20 min of heat. At the conclusion of the nocturnal challenge, PX birds had a Tr 1.0° higher than PN and C birds. Time-of-day comparisons of RR showed a significant (P < 0.05) interaction between pinealectomy and time-of-day at 30 min of exposure; the RR of PX birds was lower at night.The authors thank Dr. H. W. Norton for statistical analysis of these data.
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