The Impact of Temperature and Humidity on the Performance and Physiology of Laying Hens

SIMPLE SUMMARY: The present study investigated whether the temperature-humidity index (THI) influences the production parameters and physiology of laying hens. Two environmental conditions combining high temperature with low relative humidity (T(L)H(H)75) or vice versa (T(H)H(L)75), with the same THI value (75), were considered. The same THI value indicated equal thermal stress for laying hens. Neither T(L)H(H)75 nor T(H)H(L)75 affected laying performance, including egg production, egg weight, and egg mass, feed intake, feed conversion ratio, plasma biochemical parameters, and stress indicators. Our study suggests that laying hens exposed to the same THI values will receive similar thermal stresses. The results of this study will serve as a scientific basis for management decisions and handling laying hens under thermally challenging conditions. ABSTRACT: We investigated the effect of different ambient temperatures and relative humidity (RH) with the same temperature-humidity indices (THI) on laying performance, egg quality, heterophil to lymphocyte ratio (H/L ratio), corticosterone (CORT) concentration in blood, yolk, and albumen, and plasma biochemical parameters of laying hens. Commercial hens (Hy-Line Brown; n = 120), aged 60 weeks, were allocated to two environmental chambers. Laying hens were subjected to either one of two thermal treatments—26 °C and 70% RH (T(L)H(H)75) or 30 °C and 30% RH (T(H)H(L)75) for 28 days—with the same THI of 75. Neither T(L)H(H)75 nor T(H)H(L)75 affected laying performance, including egg production, egg weight, egg mass, feed intake, and feed conversion ratio (p > 0.05). Plasma biochemical parameters such as total cholesterol, high-density lipoprotein cholesterol, triglycerides, calcium, magnesium, and phosphorus were not altered by the environmental treatments (p > 0.05). As for stress indicators, both environmental regimes failed to affect blood H/L ratio and CORT levels in plasma, yolk, and albumen (p > 0.05), although albumen CORT levels were elevated (p < 0.05) in T(L)H(H)75 group at day 7. Hence, our study suggests that laying hens performed and responded similarly when exposed to either T(L)H(H)75 or T(H)H(L)75 characterized by the same THI. These results can serve as a scientific basis for management decisions and handling laying hens under thermally challenging conditions.