Key words:Behavior, Broilers, Fear Response, Monochromatic LED Light, Performance.The present study aimed to investigate the effect of rearing avian broiler under different monochromatic LED light color on their growth performance, physiological and fear responses. One hundred and thirty five unsexed day-old avian 48 chicks were randomly allocated into three light treatment (n=45 bird) each treatment 3 replicates (n=15 bird). The treatments were white, green, and blue light. The obtained results demonstrated that, broilers reared under blue and green light had higher body weight, weight gain, feed intake, carcass weight, carcass percent, hemoglobin, red blood cells, packed cell volume, total leucocytes count, lymphocytes, total protein, albumin, globulin and lower feed conversion ratio, bursa, liver, spleen relative weight, heterophils: lymphocytes ratio, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase compared with white light. Moreover, blue and green lights reared birds showed short tonic immobility duration and high levels of exploration in the open field test. In conclusion, rearing broilers under blue and green light for 23 h per day improve growth performance, physiological response, welfare, reduce stress and fear responses.

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In a novel approach, monochromatic blue light was used to investigate its modulatory effect on heat stress biomarkers in two commercial broiler strains (Ross 308 and Cobb 500). At 21 days old, birds were divided into four groups including one group housed in white light, a second group exposed to blue light, a 3rd group exposed to white light + heat stress, and a 4th group exposed to blue light + heat stress. Heat treatment at 33°C lasted for five h for four successive days. Exposure to blue light during heat stress reduced MDA concentration and enhanced SOD and CAT enzyme activities as well as modulated their gene expression. Blue light also reduced the degenerative changes that occurred in the liver tissue as a result of heat stress. It regulated, though variably, liver HSP70, HSP90, HSF1, and HSF3 gene expression among Ross and Cobb chickens. Moreover, the Cobb strain showed better performance than Ross manifested by a significant reduction of rectal temperature in the case of H + B. Furthermore, a significant linear relationship was found between the lowered rectal temperature and the expression of all HSP genes. Generally, the performance of both strains by most assessed parameters under heat stress is improved when using blue light.