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Physiological and Endocrinological Changes in Response to Terminal Heat Stress in Swine¹

Purdue University, West Lafayette, Indiana 47907

Abstract

Chester White pigs weighing 65 to 70 kg bearing surgically implanted catheters were placed under a surgical plane of anesthesia and subjected to programmed increases in dry bulb and dew point temperatures from 27C at a rate of 5° per hour (70 to 80% relative humidity) until heart and respiratory action ceased. Changes in plasma adrenocorticotropin (ACTH), adrenocorticoids and growth hormone levels were measured during exposure to increasing temperature. Rectal temperature, heart and respiration rates, blood gases and levels of plasma glucose and free fatty acids were monitored. Severe alterations in physiological homeostatic mechanisms occurred at rectal temperature of 41.5C. The 40- to 20-min. period ante mortem was characterized by rapid increases in rectal temperature. Extreme thermal stress caused increased heart and respiration rates, as well as elevated levels of ACTH, adrenal corticoids and lactate.

¹ Journal Paper No. 4641 of the Purdue Agricultural Experiment Station, Department of Animal Sciences.

² Present address: Department of Animal and Dairy Sciences, Auburn University, Auburn, Alabama 36830.