Abstract
Two experiments were conducted to investigate the effects of induced moisture loss on embryonic development and the immune response following an inflammatory challenge immediately post-hatch. In Experiment I, fertile leghorn eggs (n = 100) and commercial broiler eggs (n = 300) were set at 37.5°C and moisture loss was induced in one-half of the Leghorn and broiler eggs by drilling two, 1.5 mm diameter holes. The Control eggs had 0 holes. At embryonic day (ED)18, layer and broiler eggs in the 2-holes treatment had a significant (P < 0.01) increase in moisture loss compared to the control treatment (10.1% vs. 8.2%). Similarly, at ED18, the broiler eggs with 2-holes had a significant increase (P < 0.01) in moisture loss compared with control eggs (9.9% vs. 8.4%). Thymocytes from both the leghorn (104%) and broiler (62%) embryos in the 2-holes treatment had significantly increased in vitro proliferation compared with the control embryos (P ≤ 0.05). At ED18, layer and broiler embryos in the 2-holes treatment had an approximate twofold increase in the splenic CD8+/CD4+ ratio (P ≤ 0.05) and CD4+CD25+ cells percentage in both the thymus and spleen (P ≤ 0.05). At ED18, both layer and broiler embryos from the 2-holes treatment had a significant increase in splenic IL1-β, IL-6, IL-10, and TLR-4 mRNA transcription compared to the control group (P ≤ 0.05). Experiment II was repeated with 300 fertile broiler eggs. On the day of hatch, chicks were randomly distributed into one of four treatments in a 2 (0, 2 holes) × 2 (0, 500 μg lipopolysaccharide, LPS) factorial arrangement of treatments. Chicks in the LPS groups were injected intraperitoneally with 500 μg/kg BW LPS. At 24 and 48 h post-hatch, chicks hatched from eggs with 2-holes and challenged with LPS had a significant increase (P ≤ 0.05) in thymocyte proliferation at 24 h (42%) and 48 h (37%) when compared with chicks hatched from the control (0-hole; 0 μg LPS) treatment. Chicks hatched from the 2-holes treatment and challenged with the LPS had an approximately twofold higher splenic CD8+/CD4+ ratio and 1.5 fold increase in CD4+CD25+ percentage compared to control chicks (P ≤ 0.05). In chicks hatched from the 2-holes treatment, MUC2 mRNA transcription was comparable to control chicks at 24 and 48 h in response to the LPS challenge. Our data suggest that the 2-holes treatment reprograms gene transcription to facilitate cell survival via proliferation and differentiation during an LPS inflammatory challenge.
Highlights
For successful hatching, developing avian embryos require an ideal temperature, turning, humidity, and ventilation (Romanoff, 1929)
Embryos were sacrificed at ED18 and dry mass was obtained by drying the yolk-free embryos (n = 25) in an oven at 60◦C until there were no further decreases in weight
Moisture Loss at ED18 At ED18, the layer and broiler eggs in the 2-holes treatment had a significant (P < 0.01) increase in moisture loss compared to the control treatments, respectively (Table 2)
Summary
For successful hatching, developing avian embryos require an ideal temperature, turning, humidity, and ventilation (Romanoff, 1929). Avian eggs lose water during incubation and monitoring moisture loss during incubation is critical to achieving optimal hatchability and chick quality (Hoyt, 1979). Moisture loss via diffusion through eggshell pores occurs steadily during incubation and is greater than the metabolic water produced by embryonic oxidation of yolk lipids (Ar and Rahn, 1980). Incubator humidity is one of the important factors in controlling water loss during incubation (Landauer, 1967). The moisture loss percentage can range from 10 to 13% in multi-stage incubators and 9.5–12.5% of initial egg mass in single-stage incubators (Green, 2017). Induced moisture loss (>20%) achieved by drilling holes in the eggshell over the airspace on an embryonic day (ED) caused osmotic stress due to early depletion of allantoic fluid (Davis, 1987)
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