Evaluation of economic traits of White Leghorn layers under normal and controlled heat stress conditions

Based on the egg production of IWH line of WLH (n=254) during hot-dry (36–38°C and 40%RH) and hot-humid (32–34°C and 70% RH) environmental conditions, the high egg producer designated as high thermo tolerant (HT), low egg producer as low thermo- tolerant (LT) and average egg producer (control) birds were segregated. The production parameters of these birds during pre-summer were similar but the hen day egg production (HDEP) of HT group was better than LT during hot-dry summer and hot-humid summer seasons. When the HT and LT birds were placed in a psychrometric chamber and subjected to 37°C and 60% RH (THI-90) daily for 6 hours for a period of 14 days, the percent HDEP and daily feed consumption was higher in HT birds than the LT birds, however no difference was found in their daily water intake. Surface and rectal temperature was higher in HT birds than the LT birds. There was a reduction in feed intake and HDEP in LT birds than HT birds during the heat stress. After heat stress, H/L ratio and serum corticosterone levels increased in both the groups, but T₃ cholesterol and protein level decreased. There was no difference in the egg weight and other egg quality parameters except the lower albumen and yolk index, higher percent yolk and total cholesterol level in HT than LT group. Based on the above study we can conclude that high thermo-tolerant birds performed better under heat stress environment.