Rhythmic pineal melatonin biosynthesis develops in chick embryos incubated under a light (L)-dark (D) cycle of polychromatic white light. The spectral sensitivity of the embryonic pineal gland is not known and was investigated in this study. Broiler breeder eggs (Ross 308, n=450) were incubated under white, red, green or blue light under the 12L : 12D cycle. Melatonin was measured in extracts of pineal glands by radioimmunoassay. The daily rhythm of pineal melatonin levels in 20-day-old chick embryos was confirmed during the final stages of embryonic life under all four wavelengths of light with expected higher concentrations during dark- than light-times. The highest pineal melatonin levels were determined in chick embryos incubated under red and white light and lower levels under green light. The incubation under blue light resulted in the lowest melatonin biosynthesis. Pineal melatonin concentrations increased substantially on post-hatching day two compared with pre-hatching levels and we did not find differences between birds incubated and kept in either white or green light. Our results demonstrate a selective sensitivity of the chick embryo pineal gland to different wavelengths of light. Rhythmic melatonin production is suggested as a possible mechanism, which transfers information about the quality of ambient light to the developing avian embryo.

Lighting conditions during incubation can influence embryonic development, post-hatching ontogeny and production efficiency. Previous studies revealed that different light colours differently affect pineal melatonin biosynthesis in embryos and postembryonic development of broiler chickens, but physiological mechanisms mediating these effects are not known. Cold and warm white light consists of different wavelengths and therefore the aim of the present study was to explore if these two lights can differently influence the development of circadian melatonin biosynthesis, production of thyroid hormones and corticosterone, concentration of metabolites (glucose, cholesterol and triacylglycerols) as well as expression of two important immune genes, presenilin 1 and avian beta-defensin 1 (AvBD-1). We evaluated these traits in embryos before hatching (456, 460, 465, 468 and 472 h of incubation) and in hatchlings. The rhythmic profile of pineal melatonin with higher concentrations during the dark time was determined in both treatment groups. Melatonin levels increased considerably in hatchlings in comparison with embryos, but we found no difference in rhythm characteristics between groups. We did not identify any daily rhythms in plasma corticosterone and thyroid hormone levels in either studied age and no differences were found between light treatments in concentrations of thyroid hormones, corticosterone, metabolites and expression of presenilin and AvBD-1. The expected developmental increase of thyroid hormones was proved. Gene expression of presenilin increased in the duodenum of hatchlings in comparison with embryos, but the expression did not change in the bursa of Fabricius. On the other hand, expression of AvBD-1 decreased in hatchlings compared to embryos in both tissues. Based on these results, we can conclude that the colour temperature of white light did not influence endocrine and immune parameters determined in this study and probably monochromatic rather than polychromatic light should be used to influence embryonic development and postembryonic ontogeny of broiler chickens.

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Light during incubation can influence embryonic and postembryonic development of chickens, but the underlying mechanisms are poorly understood. Previous studies have demonstrated that red and blue lights during incubation had opposite effects on the development of embryonic melatonin biosynthesis; red light results in the highest and blue light in the lowest amplitude of the daily rhythm. Therefore, in this study, we investigated if exposure to monochromatic red (632 nm) and blue (463 nm) light during incubation can differently influence growth, selected biochemical (glucose, cholesterol, triacylglycerols) and endocrine (corticosterone and thyroid hormones) traits and behavioural parameters during postembryonic development in broiler chickens. For analysis, we used 10 and 11 hatchlings incubated in red and blue light, respectively and 10 birds per each group (six males and four females) in 3-weeks-old broilers. During the rapid growth phase (days 18, 20 and 21 of age), higher body weight was recorded in broilers incubated under red compared to blue light, whereas endocrine and metabolic traits did not differ between the treatments. The improved growth rate was related to behavioural traits, mainly because chickens incubated in red light exhibited more passive (resting, standing, preening, dust bathing) and less active behaviours (walking, foraging, fighting, wing-flapping) than the blue-light incubated birds. The time spent for eating and drinking and the results of the tonic immobility test did not differ between both groups. Our results suggest that red and blue monochromatic light during incubation can differently program the postembryonic development of broilers, with possible consequences for their growth and welfare.