Circulating metabolic and reproductive hormone changes in laying hens kept under various heat-combating systems

The objective of the present study was to observe the circulating metabolic, reproductive, and stress hormones in laying hen performance under different heat-combating systems (HCSs). A total of 500 White Leghorn pullets at 24 weeks of age were subjected to four HCSs, i.e. desert cooling (DC), water sprinkling (WS), time limit feeding (TLF), and ascorbic acid (AA) supplementation, at environmental temperatures from 32.30 to 40.80 degrees C with 76.40% relative humidity. Blood was collected before heat stress, at peak stress, and after heat stress to collect plasma. The results of the 24-week stress period showed significantly less circulating T-3, T-4, estrogen, and progesterone in the control group in the peak stress period, whereas corticosterone was significantly higher. The plasma T-3, T-4, and estrogen and the egg production percentage remained significantly higher in the DC system as compared to other HCSs and the control. In comparison, the plasma progesterone level was significantly increased with lower T-4 in the AA supplementation group than the other HCSs. Our results validate the potential role of the DC system in protecting birds from environmental heat stress effects and subsequent improvement in egg production.