Impact of temperature-humidity index on egg-laying characteristics and related stress and immunity parameters of Japanese quails

The aim of this study was to investigate the effect of temperature-humidity index (THI) level on productive parameters, welfare, and immunity in Japanese quails. One hundred and eighty (180) birds of Japanese quail, 14 weeks old, were used. Birds were divided randomly into three equal groups, control (at low THI, less than 70), H₁ (at moderate THI, 70–75), and H₂ (at high THI, 76–80). Birds in the control group had higher body weight (281.2 g, p = 0.001), egg mass (745 g, p = 0.001), fertility (85.4 %, p = 0.039), hatchability (80.4 %, p = 0.001), and immune response titer to Newcastle disease virus (p = 0.031), compared with H₂ group. Furthermore, the thermoneutral group had higher internal egg quality score [albumen height (5.14 mm, p = 0.001), yolk height (10.88 mm, p = 0.015), yolk index (42.32 %, p = 0.039), and Haugh unit (92.67, p = 0.001)]. Nevertheless, there were no significant differences in fertility percentage, immune response, and corticosterone concentration between control and H₁ group. Birds in the H₂ group had the lowest total leucocytic count and lymphocyte percentage (p = 0.001 and 0.020, respectively) but the highest H/L ratio (0.83, p = 0.001). Corticosterone concentration was lower in control and H₁ groups (5.49 and 6.41 ng/mL, respectively, p = 0.024) than that in H₂ group. Japanese quail exposed to heat stress revealed drop in production and immunological parameters, as well as a detrimental effects on welfare. Thus, practical approaches might be used to reduce the detrimental effects of greater THI level.