Effect of pre-hatch incubator lights on the ontogeny of CNS opsins and photoreceptors in the Pekin duck

Abstract

The Pekin duck is a valuable agricultural commodity globally and in the United States. Pekin ducks are seasonal breeders; they are sensitive to light and thus, research on the neuroendocrine and behavioral responses are needed to maximize production and to improve their welfare. There is compelling evidence that specific wavelengths of light may adversely alter the growth and welfare of meat (grow out) ducks. However, despite a birds' dependence upon light, in commercial poultry hatcheries, incubators almost exclusively hold eggs in the dark. Therefore, our objective was to determine the effects of lighting on the expression of retina photoreceptors (RPs) and deep brain photoreceptors (DBPs) during duck embryological development. Two groups of ducks were raised with and without light over 21 d from egg laying, embryonic day 0. Brain and retinal tissues were collected at embryonic days 3, 7, 11, 16, and 21 of a 24 d incubation period. qRT-PCR was performed on RPs (OPN1LW, OPN2SW, OPN1SW, MAFA, RHO, and RBP3) and the DBP OPN4M from retinal and brain samples, respectively. We find that the presence and absence of light during pre-hatch incubation, had no influence on the expression of any retinal photoreceptor. However, a late embryological increase in DBP OPN4M expression was observed. Taken together, the impact of light during pre-hatch incubation does not impact the overall post-hatch production. However, future directions should explore how OPN4M pre-hatch activation impacts Pekin duck post-hatch development and growth.

Keywords: OPN4M; Pekin duck; deep brain photoreceptors; ontogeny; photoreceptors; retina.

Figure 1

Production data. (A) Percent of clear eggs, early deads, infects, and rots. There was no difference in the number of early dead, infected, or rotted egg percentages between lighted and dark incubation. (B) Hatchability percentage. There was no difference in the percent of eggs hatched or the percentage of ducklings lost due to neonatal death between those raised in light and dark incubators. (C) Body weight (kg) of ducks at market weight (35 d), eviscerated carcass weight, and percent mortality at 1 and 2 wk of age. There was no difference in body weight or eviscerated carcass weight, week-old weight, and 2-wk old weight of birds that were incubated in light or dark incubators. Data are presented as mean ± SEM. Abbreviations: Evis, eviscerated; Mort, mortality; Wk, week.

Figure 2

The absence of light does not significantly impact the relative gene expression of cones (OPN1LW, OPN2SW, and OPN1SW) and rods (MAFA, RHO, and RBP3) in the retina across a development. (A–E) No main effect of time or treatment was found using repeated measures mixed-effect ANOVA. (F) A main effect of Treatment (F(1,62) = 4.132, P < 0.05) was found. No main effect of Time (F(2.198,34.07) = 1.644, P > 0.05) nor interaction (F(4,62) = 0.8269, P > 0.05) was observed using a repeated measure mixed-effect ANOVA. Posthoc analysis did not show significant differences between dark and light treatment groups at any day postincubation. Data are presented as mean ± SEM. Abbreviation: HKGs, House keeping genes.

Figure 3

OPN4M gene expression increases during embryonic development. (A) A main effect of Time (F_{(1.517, 26.17)} = 19.38, P < 0.05) and a significant interaction between Time × Treatment (F_{(4, 69)} = 2.512, P < 0.05) was found. No main effect of Treatment (F_(1,69) = 0.02465, P > 0.05) was observed using a repeated measure mixed-effect ANOVA. (B) Light and Dark groups combined. Brown-Forsythe (F_{(4, 33.17)} = 19.48, P < 0.05) and Welch's (F_{(4, 32.34)} = 13.96, P < 0.05) ANOVA. Post-hoc using Dunnett's T3 multiple comparisons test. Data are presented as mean ± SEM. Abbreviation: HKGs, house keeping genes.