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.

Summary An F2 population of 239 chickens was obtained by an intercross between Nagoya (NAG), a native Japanese breed with low growth, and White Plymouth Rock (WPR), a Western breed with high growth. Using SNP markers obtained by restriction site‐associated DNA sequencing, genome‐wide QTL analysis was performed and it revealed three QTL for early postnatal growth in the F2 population at genome‐wide 5% significance levels. The most highly significant QTL affecting body weights at 2–4 weeks of age and weight gains at 2–3 and 0–4 weeks was located on GGA4 between 34.0 and 65.6 Mb with LOD scores of 3.9–5.9 and it explained 4.9–9.9% of the total variance of the traits. The analysis provided evidence for significant QTL on GGA2 between 105.6 and 125.2 Mb (LOD = 4.6) and on GGA1 between 51.1 and 61.6 Mb (LOD = 4.0) which had effects on body weight at 3 weeks and body weight gain at 0–1 week respectively. These two genomic regions explained 6.6 and 6.9% of the phenotypic F2 variance of the corresponding traits respectively. The allele derived from WPR at all QTL increased the corresponding traits. Neither sex‐specific nor epistatic QTL was detected. The results showed that the GGA4 QTL affecting multiple traits is a key locus responsible for early growth in our chicken cross, suggesting that this QTL may make a great contribution to genetic improvement of growth performance of the NAG breed with a low growth rate.

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