Abstract
The physiological responses and the changes of plasma glucocorticoids concentrations of steers under severe hot and humid conditions were studied. The six Holstein steers were exposed to the six enviromental conditions of temperature and humidity within the range of 33-42°C and 60-80% in relative humidity.
1) The rectal temperature raised above 42°C in all steer and the time required to reach that temperature level was shortened as the effective temperature increased.
2) After the exposure, the respiration rate was increased rapidly to the maximum level followed by gradual decrease.
3) The heart rate was increased remarkably during the course of the death, while the rectal temperature was always above 42°C. The heart rate tended to decrease just before the death.
4) Only the conditions in which the steers were forced to death induced the increase of the plasma glucocorticoids, while the survived steers exhibited no concentration change in plasma glucocorticoids.
