In ovo green light photostimulation during the late incubation stage affects somatotropic axis activity

Abstract

Targeted green light photostimulation during the last stage of broiler incubation increases expression of the somatotropic axis. The purpose of this study was to further shorten the in ovo green light photostimulation and determine the critical age for photostimulation in broilers embryos, as a future strategy for broiler incubation. Fertile broilers eggs (n = 420) were divided into 5 treatment groups. The first group was incubated under standard conditions (in the dark) as the negative control group. The second was incubated under intermittent monochromatic green light using light-emitting diode lamps with an intensity of 0.1 W/m² at shell level from embryonic day (ED) 0 of incubation until hatch, as a positive control. The third, fourth, and fifth groups were incubated under intermittent monochromatic green light from ED 15, 16, and 18 of incubation, respectively, until hatch. All treatment groups showed elevated somatotropic axis expression compared with the negative control, with the group incubated under monochromatic green light from ED 18 until hatch showing results closest to the positive control. This suggests that broiler embryos can be exposed to in ovo green light photostimulation from a late stage of incubation (when transferring the eggs to the hatchery) and exhibit essentially the same outcome as obtained by photostimulation during the entire incubation period.

Keywords: broiler; critical period; green light photostimulation; somatotropic axis.

Figure 1

Plasma growth hormone levels, between ED12 and ED20, of broiler embryos incubated in the dark as a negative control (dark) or under monochromatic green light from different days of incubation to day of hatch (GD0–20, GD15–20, GD16–20, and GD18–20). Data are presented as mean ± SEM. Means of the groups on a specific day with different lowercase letters differ significantly (P < 0.05). Abbreviations: ED, embryonic day; GH, growth hormone.

Figure 2

Hypothalamic GHRH mRNA expression, between ED10 and ED20, of broiler embryos incubated in the dark as a negative control (dark) or under monochromatic green light from different days of incubation to day of hatch (GD0–20, GD15–20, GD16–20, and GD18–20). Data are presented as mean ± SEM. Means of the groups on a specific day with different lowercase letters differ significantly (P < 0.05). Abbreviations: ED, embryonic day; GHRH, growth hormone-releasing hormone.

Figure 3

Liver GHR mRNA expression, between ED10 and ED20, of broiler embryos incubated in the dark as a negative control (dark) or under monochromatic green light from different days of incubation to day of hatch (GD0–20, GD15–20, GD16–20, and GD18–20). Data are presented as mean ± SEM. Means of the groups on a specific day with different lowercase letters differ significantly (P < 0.05). Abbreviations: ED, embryonic day; GHR, growth hormone receptors.

Figure 4

Liver IGF-1 mRNA expression, between ED10 and ED20, of broilers incubated in the dark as a negative control (dark) or under monochromatic green light from different days of incubation to day of hatch (GD0–20, GD15–20, GD16–20, and GD18–20). Data are presented as mean ± SEM. Means of the groups on a specific day with different lowercase letters differ significantly (P < 0.05). Abbreviations: ED, embryonic day; IGF-1, insulin-like growth factor 1.