Phenotypic developmental plasticity induced by preincubation egg storage in chicken embryos (Gallus gallus domesticus)

Abstract

The developing chicken blastoderm can be temporarily maintained in dormancy below physiological zero temperature. However, prolonged preincubation egg storage impairs normal morphological and physiological development of embryos in a potential example of fetal programming (in this case, "embryonic programming"). We investigated how preincubation egg storage conditions (temperature, duration, hypoxia, and hypercapnia) affects viability, body mass, and physiological variables and functions in day 15 chicken embryos. Embryo viability was impaired in eggs stored for 2 and 3 weeks, with the effects greater at 22°C compared to 15°C. However, embryo size was reduced in eggs stored at 15°C compared with 22°C. Phenotypic change resulting from embryonic programming was evident in the fact that preincubation storage at 15°C diminished hematocrit (Hct), red blood cell concentration ([RBC]), and hemoglobin concentration ([Hb]). Storage duration at 15°C more severely affected the time course (2, 6, and 24 h) responses of Hct, [RBC], and [Hb] to progressive hypoxia and hypercapnia induced by submersion compared with storage duration at 22°C. The time-specific regulation of acid-base balance was changed progressively with storage duration at both 22 and 15°C preincubation storages. Consequently, preincubation egg storage at 22°C resulted in poor viability compared with eggs stored at 15°C, but size and physiological functions of embryos in eggs stored for 1-2 weeks were worse in eggs stored in the cooler than stored under room conditions. Avian eggs thus prove to be useful for examining developmental consequences to physiology of altered preincubation thermal environment in very early stages of development (embryonic programming).

Keywords: Acid–base balance; chicken embryos; fetal programming; hematology; preincubation egg storage; viability.

Figure 1

Changes in viability (panel A1, A2), body mass (panel B1, B2), and egg water loss (panel C1, C2) in d15 embryos stored as eggs for 3 weeks at 22 and 15°C in six replicates of storage procedure. Viability of embryos in each group of 22 and 15°C storage procedures is percent ratio of number of viable embryos (shown in Table 2) to 30 eggs. Body mass is mean value of viable embryos and water loss is mean value of 30 eggs. The different symbols in panels A1, B1, and A2 indicate significant difference between mean values of storage durations (0 (nonstorage), 1, 2, and 3 weeks). When the interaction between storage temperature and storage duration was not significant, the significance symbols are shown only in a 22°C panel. Mean values ± 1 SEM are plotted in panels B1, B2, C1, and C2.

Figure 2

The relation between viability and body mass in d15 embryos stored as eggs at 22 and 15°C for 0 (nonstorage), 1, 2, and 3 weeks. Individual values of viability and body mass are the same as those in Figure 1.

Figure 3

Time‐specific changes in body mass (panel A1, A2), blood osmolality (B1, B2), and lactate concentration ([La⁻]) (C1, C2) during 24 h of water submersion in d15 embryos stored as eggs for 0 (nonstorage), 1, and 2 weeks at 22°C and additionally 3 weeks at 15°C. Mean values ± 1 SEM are plotted (N is shown in Table 3). Means not significantly different from each other are grouped within the same box. Different letters indicate significant difference between submersion times for all storage procedures (except 3 weeks) combined. When the interaction between storage temperature and submersion time was not significant, the significance letters are shown only in a 22°C panel.

Figure 4

Time‐specific changes in hematocrit (Hct) (panel A1, A2), red blood cell concentration ([RBC]) (B1, B2), and mean corpuscular volume (MCV) (C1, C2) during 24 h of water submersion in d15 embryos stored as eggs for 0 (nonstorage), 1, and 2 weeks at 22°C and additionally 3 weeks at 15°C. Mean values ± 1 SEM are plotted (N is shown in Table 3). Means not significantly different from each other are grouped within the same box. Different letters indicate significant difference between submersion times for all storage procedures (except 3 weeks) combined.

Figure 5

Time‐specific changes in hemoglobin concentration ([Hb]) (panel D1, D2), mean corpuscular hemoglobin (MCH) (E1, E2), and mean corpuscular hemoglobin concentration ([MCHb]) (F1, F2) during 24 h of water submersion in d15 embryos stored as eggs for 0 (nonstorage), 1, and 2 weeks at 22°C and additionally 3 weeks at 15°C. Mean values ± 1 SEM are plotted (N is shown in Table 3). Means not significantly different from each other are grouped within the same box. Different letters indicate significant difference between submersion times for all storage procedures (except 3 weeks) combined.

Figure 6

Time‐specific changes of acid–base disturbances during 24 h of water submersion in d15 embryos stored as eggs for 0 (panel A1), 1 (B1), 2 (C1), and 3 weeks (0 h only) (D1) at 22°C, and in eggs stored for 0 (panel A2), 1 (B2), 2 (C2), and 3 (D2) weeks at 15°C. Mean values ± 1 SEM are plotted (N is shown in Table 3). The time‐specific changes in eggs without storage (0 week, A1 and A2) are connected by broken lines and shown in other panels for visual comparison with eggs stored for 1, 2, and 3 weeks. The dotted curves are pco ₂ isopleths of which values are indicated by small numerical figures. The diagonal solid line is buffer line indicating buffer value of −16 mmol L⁻¹ pH ⁻¹.