Abstract

Introduction

Heat stress is one of the most serious problem facing poultry production in all subtropical countries during summer [1]. The severity of heat stress is due to the resultant oxidative stress which is characterized by accumulation of oxygen reactive species (ROS) in an excess to cellular antioxidants [2–4]. Besides heat exposure, vigorous bird handling, presence of oxidize dietary oils, and infection are associated with ROS formation [3, 5, 6]. ROS accumulation is accompanied by disturbances of cellular balance and modulation of several biological macromolecules including nucleic acid and protein [7]. The cellular antioxidant enzymes represent the first defense system which is responsible for restoring cellular hemostasis. Thus, the increase in the antioxidant enzyme activities including superoxide dismutase (SOD) and catalase (CAT) protects the cells from heat stress-ROS-associated damaged effects. This response greatly differs according to the heat stress conditions, species, and affected tissue [2].

Moreover, one of the main other consequences of heat stress is protein damage and subsequent accumulation of unfolded proteins [8, 9]. Affected cells increase the expression of chaperone proteins and heat shock protein (HSPs), leading to proteostasis and thermotolerance [10]. The HSPs include Hsp40, Hsp60, Hsp70, Hsp90, Hsp110, and the small HSPs. HSP70 and HSP90 are the most conserved HSPs. They work to protect the cell and prevent the aggregation of unfolding protein [11]. Additionally, HSPs protect the cells from heat shock deleterious impacts and enhance tissue repair [12]. HSP expression is regulated mainly at the level of transcription by four heat shock transcription factors (HSFs). HSFs include HSF-1, HSF-2, and HSF-4 (specific to mammals) and HSF-3, which is avian specific [13]. HSFs modify HSP expression through interaction with a specific DNA sequence (heat shock element (HSE)) in their promoter [14, 15]. Hence, they regulate the HS response.

Different approaches have been done to control the destructive effects of heat stress. Among which were inclusion of feed additives in the diet and water, as well as light management [16]. However, lighting management studies in the alleviation of heat stress deleterious effects are still lacking. Previous studies looked at the effect of different monochromatic lights (white, red, green, and blue) on the broiler immune response and the breed performance [17–20]. Light management was found to increase productivity and improve animal welfare [18, 20, 21]. Thus, light color has been considered as a powerful management that can be used to modify many physiological, immunological, and behavioral pathways [22, 23]. For instance, blue light has been shown to have calming effect by reducing the negative impact of different stressors [24, 25]. Blue light modulates peripheral blood T lymphocytes proliferation, the response to Newcastle disease virus vaccine, heterophils to lymphocytes (H/L) ratio, and interleukin-1β (IL-1β) expression [22, 23]. In addition, using blue light significantly increases the numbers of intestinal intraepithelial lymphocytes, goblet cells, and IgA⁺ cells [26]. Moreover, blue light significantly improves meat quality by decreasing lipid peroxidation and improving antioxidant activities by enhancing SOD, GHS, and total antioxidant capability activities and reduced MDA content both in breast and thigh muscles [27].

The aim of their work was to investigate effects of the monochromatic blue light (BL) on alleviating the negative impact of induced cyclic chronic heat stress in commercial broiler strains. They investigated the regulatory effect of using monochromatic blue light during heat stress on heat stress biomarkers activity including antioxidant enzyme activity, histopathological changes in the liver tissue, HSP gene expression, and bird’s temperature.

Conclusion

Their findings represent the first reported data on the role of monochromatic blue light in regulating the bird’s resistance to heat stress. Replacing white light by the blue one during heat stress would modify the heat shock biomarker activities which might enhance the bird’s resistance to negative impacts of heat stress. Finally, theirresults suggest that Cobb 500 have a better response to blue light than Ross 308. Therefore, using blue light during heat stress represents a cheap tool to manage and control heat stress in poultry farms. Therefore, scientists strongly recommend using blue light in poultry houses during summer.

References