Effects of relative humidity on physiology and behavior of laying hens exposed to high ambient temperatures

This study investigated how different relative humidity (RH) would impact behavior and physiology of laying hens. One hundred-eighty laying hens (Hy-Line Brown), aged 68-week-old (1,908 +/- 78 g), were exposed to daily ambient temperatures of 30 degrees C with RH set at 25% (RH25), 50% (RH50), or 75% (RH75) for 12 h a day (9:00 am to 9:00 pm) from 70 to 74 weeks of age. All hens had been raised at 24 degrees C and 50% RH during 2-week adaptation period. Each RH treatment consisted of 10 replicates with 6 hens each in a completely randomized design. Results indicated that rectal temperature, respiratory rate, and heart rate were increased (P <= 0.05) in the RH75 group compared with the RH25 and RH50 groups. Plasma malondialdehyde concentrations were elevated in the RH75 group compared RH50 at 3, 7, and 21 days (P <= 0.05) following the RH exposure. Plasma glutathione peroxidase activity was lowered (P <= 0.05) in the RH75 group compared with the RH25 and RH50 groups at 21 days. Increasing RH led to decreased feeding behavior but showed a tendency to increase drinking behavior. Wings elevated and panting behaviors were higher in the RH75 group compared with the RH25 and RH50 groups (P <= 0.05). In conclusion, these findings suggest that elevated RH at constant ambient temperature could negatively influence the behavior and physiology of laying hens.