Abstract
Simple SummaryThe 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 (TLHH75) or vice versa (THHL75), with the same THI value (75), were considered. The same THI value indicated equal thermal stress for laying hens. Neither TLHH75 nor THHL75 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.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 (TLHH75) or 30 °C and 30% RH (THHL75) for 28 days—with the same THI of 75. Neither TLHH75 nor THHL75 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 TLHH75 group at day 7. Hence, our study suggests that laying hens performed and responded similarly when exposed to either TLHH75 or THHL75 characterized by the same THI. These results can serve as a scientific basis for management decisions and handling laying hens under thermally challenging conditions.
Highlights
We investigated the time-dependent changes in productive and physiological responses throughout heat stress, which seemed to be a robust approach to evaluate the stress response, if any, of laying hens exposed to the same temperature-humidity indices (THI)
When hens were exposed to THI 75 conditions with either TL HH 75 or TH HL 75, no differences were observed in any of the measured variables, including hen-day egg production, egg weight, egg mass, and feed conversion ratio
It can be concluded from this study that laying hens exposed to different environmental conditions with same THI (i.e., TL HH 75 or TH HL 75) exhibit no differences in laying performance, egg quality, and plasma biochemical profiles
Summary
The optimum temperature (thermoneutral zone) for laying hens allowing optimal performance is between 19 and 22 ◦ C [1]. Laying hens exposed to ambient temperatures above the thermoneutral zone experience heat stress that triggers physiological defense mechanisms, including panting [2]. Laying hens are vulnerable to heat stress due to their extended production cycle of up to 74 weeks of age [2], lack of sweat glands, feathers, and generation of high metabolic body heat [3]. Heat stress per se affects egg production and quality [4,5], as well as physiological [6,7] and stress responses [8] of laying hens. When subjected to heat stress, laying hens significantly reduce their feed intake (38.8%), laying performance (5.0%), and body weight (5.2%) at 24 weeks of age [4]
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