J. Anim Sci.
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J. Anim Sci. 1974. 38:819-822.
© 1974 American Society of Animal Science
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Plasma Corticoids of Angus Heifers in Programmed Circadian Temperatures of 17 to 21 C and 21 to 34 C1, 2,

H. L. Miller3 and C. W. Alliston

Purdue University4, West Lafayette, Indiana 47907

Abstract

Total glucocorticoid levels were studied in eight 14-month-old Angus heifers maintained at control (17 to 21 C diurnal variation) and experimental (21 to 34 C diurnal variation) temperature regimes. Rectal temperatures were significantly (P<.01) increased by the experimental temperature regime, indicating that these conditions exceeded thermoneutrality.

During exposure to the experimental temperature, corticoid levels were higher at 0800 and 1600 hr. for the first week and lower for the remainder of the estrous cycle as compared with the control temperature. Mean levels for the entire estrous cycle were only slightly increased by the experimental temperature regime (8.3 ± .4 vs. 7.6 ± .4 ng/ml, P>.05). At both temperature regimes corticoid levels were generally higher on the day of estrus and lower during the remainder of the estrous cycle. Increased ambient temperature resulted in greater variation of total corticoid levels. Days were the only significant (P<.05) main effect, presumably due to a combination of thermal effects and the increase of corticoid levels associated with estrus.

Footnotes

1 Published with the approval of the Director of the Purdue University Agricultural Experiment Station as Publication No. 5195 of the Journal Series.

2 The authors gratefully acknowledge the contributions of Dr. E. D. Aberle in making facilities available and of Barbara Ailor for technical assistance.

3 Present address: Department of Animal Science, South Dakota State University, Brookings, South Dakota 57006

4 Department of Animal Sciences.






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Copyright © 1974 by the American Society of Animal Science.