Sex-based responses of plasma creatine kinase in broilers to thermoneutral constant and cyclic high temperatures

1. The plasma creatine kinase (CK) activities of male and female broilers under different temperature regimens were studied to investigate the suitability of plasma CK as an indicator of muscle damage due to heat exposure (HE). 2. This study characterises the responses of plasma CK concentration of Arbor Acres broilers to thermoneutral (TN) constant (22°C) or warm cyclic (WC) temperatures (ranging from 27·9°C to 37·9°C). 3. The daily mean CK of the females tended to be higher than those of the males, and significant differences in plasma CK were observed between the genders during the first 5-d test period, namely 2-d TN constant and 3-d WC temperatures. 4. During a 5-d HE to the WC regimens, CK of both genders fluctuated with HE time but exhibited somewhat different profiles. Specifically, the daily mean CK of the females was significantly higher on d 5 of HE than any other daily means, whereas significant difference in daily CK of the males occurred on d 4 of HE. 5. Repetitive blood sampling over 5 d of HE had significant effects on the plasma CK of the females regardless of the number of repeated bleeding times. 6. Profiles of the plasma CK for each gender during d 1 of HE were similar to those under the TN condition, implying that heat stress affects the range of broiler plasma CK concentration but with a 1-d lag. 7. Plasma CK activities of female and male broilers showed a response to HE. However, both the gender and the time of blood sampling should be taken into account when plasma CK is used as an indicator of HE for market-size broilers.