J. Anim Sci.
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J. Anim Sci. 1973. 36:369-373.
© 1973 American Society of Animal Science
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Plasma Corticosteroids in Hereford Bulls Exposed to High Ambient Temperature1

W. E. Rhynes2 and L. L. Ewing3

Department of Physiological Sciences, Oklahoma State University, Stillwater 74074

Abstract

Eight Hereford bulls were exposed continuously for 7 weeks to 35.5 C; 50% RH after they had previously been maintained at 21.0 C; 50% RH for 7 weeks. Response to heat by individual bulls was evaluated by measuring rectal temperature, respiration rate, and cortisol and corticosterone concentrations in peripheral blood at weekly intervals throughout both temperature periods, and daily during the first week of exposure to 35.5 C. Heat treatment imposed a thermal load on the bulls that resulted in significant (P<.01) elevations in rectal temperature and respiration rate. Heat did not significantly alter corticosterone concentration in peripheral plasma from the control value of 3.0 ng/ml. In contrast, cortisol concentration in peripheral plasma decreased from 18.03 to 11.93 ng/ml (P<.05) during the first day of heat exposure and remained at approximately this level for the duration of the heat treatment. These results prove conclusively that depression of cortisol concentration in peripheral plasma of Hereford bulls is one consequence of exposure to high ambient temperature.

Footnotes

1 This investigation was supported in part by U. S. Public Health Service Research Grant HD-00636 and HD-05795 from the National Institute of Child Health and Human Development, in part by U. S. Health Service General Research Support Grant FR-5567 and in part by Institutional Cancer Research Grant Number IN-91.

2 W. E. Rhynes was a NICHD Special Research Fellow.

3 L. L. Ewing is a recipient of a Research Career Development Award HD-39926.






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Copyright © 1973 by the American Society of Animal Science.