Fig. 1. Temporal changes in enzyme activities in the serum of experimental chickens. (A) The levels of aspartate aminotransferase (AST) showed an obvious increase from 10 h of heat exposure in the heat stress (HS) group to the end of the test, while the AST in the aspirin administered before heat stress (ASA+HS) and aspirin administration (ASA) groups stayed relatively stable. (B) The levels of creatine kinase (CK) showed an increasing tendency after 3 h of HS in the HS group, while no difference was detected in the CK of the ASA+HS and ASA group (except for a decline at 10 h). (C) The levels of lactate dehydrogenase (LDH) showed a significant increasing tendency in the HS group, with that of the ASA-HS group showing a marked rise after 5 h of HS, then returning to the basal level. No difference was detected for LDH in the ASA group, except for an increase at 7 h. Differences between levels of enzymes in every group at different times and that at 0 h in the HS group are indicated by ^*p < 0.05, and by ^**p < 0.01. U/L, unit of enzyme activity/L.