Changes of Plasma Growth Hormone, Insulin-Like Growth Factors-I, Thyroid Hormones, and Testosterone Concentrations in Embryos and Broiler Chickens Incubated under Monochromatic Green Light

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Previous studies showed that monochromatic green light stimuli during embryogenesis accelerated posthatch body weight and pectoral muscle growth of broilers. In this experiment, we further investigated whether the regulation of broiler embryonic or posthatch growth by green light stimulus during incubation is associated with the changes of some important hormones at different ages of embryos and broiler chickens. Fertile broiler eggs (Arbor Acres, n=880) were pre-weighed and randomly assigned 1 of 2 incubation treatment groups: i) dark condition (control group), and ii) monochromatic green light group (560 nm). The monochromatic lighting systems sourced from light-emitting diode lamps were equalised at the intensity of 15 lux (lx) at eggshell level. The dark condition was set as a commercial control from day one until hatching. After hatch, 120 day-old male chicks from each group were housed under white light with an intensity of 30 lx at bird-head level. Compared with the dark condition, chicks incubated under the green light showed significantly higher growth hormone (GH) levels from 19 d of embryogenesis (E19) to 5 d of posthatch (H5), and higher plasma insulinlike growth factor (IGF-I) levels from both E17 to E19 and H3 to H35. No significant differences were found in plasma thyroxine, triiodothyronine, and testosterone in embryos or hatched birds between the 2 groups. These results indicate that somatotropic axis hormones (GH and IGF-I) may be the most important contributor to chicken growth promoted by green light stimuli during embryogenesis.