Author : Phan Quang Vinh

Summary : Four experiments were done to: a) evaluate the possibility of using serum adrenocorticotrophic hormone (ACTH) levels right after weaning and serum creatine phosphokinase as stress-susceptability index; b) determine the castration effect on stress-susceptability; and c) compare the responses of animals exposed to solar heat stress with and without propranolol treatment in terms of pulse rate (P), respiration rate (R), rectal temperature (RT), blood lactate, and serum CPK activity. Logarithmic activity of serum CPK was found to decrease lineary with increasing body weight (P<0.05). Serum CPK activity was affected by genotypes but not by castration, sex, and stress-susceptibility. It is suggested that serum ACTH right after weaning and serum CPK activity at any growth stage should not be used as stress-index for individual screening. In pigs exposed to solar heat stress, significant multiple regressions of RT against ambient temperature (AT) and intervals of exposure time were established. Based on these regressions, stress-susceptible (SS) and stress resistant (SR) pigs were classified by tentative setting an RT of 41.7 degree C as the upper limit which an SR pig may attain after 90 minutes under the upper exposure condition where AT changes from 32.2 degree C to 42.2 deg C. Porcine stress-susceptibility did not seem to be related to sex, and castration. P, R, RT at +30, +90, +150 minutes, post-exposure serum CPK activity were found to significantly increase from pre-exposure values of respective parameters except blood lactate.