Effects of Cool Water Supply on Laying Performance, Egg Quality, Rectal Temperature and Stress Hormones in Heat-Stressed Laying Hens in Open-Type Laying Houses

We used an animal welfare-certified open-type layer farm and analyzed the egg production, egg quality, rectal temperature, and yolk corticosterone levels of laying hens supplied with cool water during the summer season (avg. 33 ± 3.89 °C). A total of 5750 Hy-Line Brown laying hens at 53 weeks of age were used, and two treatment groups were established: a control group (2900 hens) and a cool water treatment group (2850 hens). The water temperature of the control group was 25.3 ± 0.8 °C and the cool water was 20.1 ± 0.3 °C; all other environment parameters (lighting, ventilation, temperature, feed, etc.) were the same. The experiment was conducted for a total of 9 weeks (between July and September 2024), and during this period, the temperature-humidity index (THI) inside the breeding facility averaged 85.21, which corresponds to the cool water supply range (80 < THI < 90). As a result, the cool water treatment group maintained high productivity and showed low mortality (<i>p</i> < 0.05). In addition, hens provided with cool water showed high eggshell strength and low yolk corticosterone levels (<i>p</i> < 0.05). The core finding of this study is that the supply of cool water in summer is effective in maintaining the productivity and egg quality of laying hens and reducing HS. This is significant in that it suggests it is possible to manage laying hens in summer in a simple way, and it can also be used as basic data for designing future studies, such as using a combination of natural products including vitamins and minerals.