Physiological Responses of Stress Susceptible and Stress Resistant Pigs to Heat Stress

Abstract

Stress susceptible and stress resistant Hampshire barrows and gilts were subjected to a controlled heat stress of 35C, 65% relative humidity from 1100 to 1400 hr. and certain physiological responses were measured. During heat stress, body temperatures and respiration rates of both groups of pigs increased. Stress susceptible animals had greater elevations in body temperature. Blood pH of samples obtained via indwelling catheters from the anterior vena cava of susceptible pigs increased during the heat period, whereas blood pH of resistant animals did not change significantly. In both groups of animals, venous pCO₂ and pO₂ decreased during heat stress. Plasma adrenal corticoids increased significantly during the first replication of heat stress but did not follow this pattern when the stress was repeated, suggesting accumulative effects of stress on adrenal response or acclimation to the treatment. Stress susceptible and stress resistant pigs had similar plasma adrenal corticoid concentrations. Heat stress did not significantly affect serum creatine phosphokinase or glutamic-oxaloacetic transaminase activity or plasma protein concentration. As compared to the resistant pigs, susceptible animals had higher plasma protein concentrations which may contribute to increased blood buffering capacity. Copyright © 1974. American Society of Animal Science . Copyright 1974 by American Society of Animal Science.