Perches as Cooling Devices for Reducing Heat Stress in Caged Laying Hens: A Review

SIMPLE SUMMARY: High ambient temperature is a critical environmental challenge to the egg industry worldwide. Laying hens that are under heat stress are unable to maintain a balance between body heat production and heat loss, leading to hyperthermia, which substantially disturbs physiological homeostasis and consequently reduces all parameters of production performance, e.g., egg production, egg quality, feed intake, feed efficiency rate, and longevity—ultimately causing substantial economic losses. To alleviate these deleterious effects, the egg industry and poultry scientists are working towards developing cooling methods to prevent heat stress. This review summarizes our recent discoveries that perches can be used as cooling devices to avoid or reduce heat stress detrimental effects on hen production, health, and welfare. Our results provide a novel strategy: perches, one key furnishment in cage-free and enriched colony facilities of modern laying hens, could be modified as cooling devices to improve hen thermal comfort during hot seasons. ABSTRACT: Heat stress is one of the most detrimental environmental challenges affecting the biological process and the related production performance of farm animals, especially in poultry. Commercial laying hens have been bred (selected) for high egg production, resulting in increased sensitivity to heat stress due to breeding-linked metabolic heat production. In addition, laying hens are prone to heat stress due to their inadequate species-specific cooling mechanisms resulting in low heat tolerance. In addition, hens have no sweat glands and feathering covers almost their entire body to minimize body heat loss. The poultry industry and scientists are developing cooling methods to prevent or reduce heat stress-caused damage to chicken health, welfare, and economic losses. We have designed and tested a cooling system using perches, in which chilled water (10 °C) circulates through a conventional perch passing through the layer cages to offer the cooling potential to improve hen health, welfare, and performance during acute and chronic periods of heat stress (35 °C). This review summarizes the outcomes of a multi-year study using the designed cooled perch system. The results indicate that conducting heat from perching hens directly onto the cooled perch system efficiently reduces heat stress and related damage in laying hens. It provides a novel strategy: perches, one key furnishment in cage-free and enriched colony facilities, could be modified as cooling devices to improve thermal comfort for hens during hot seasons, especially in the tropical and subtropical regions.