The developmental pattern of calcium mobilisation during embryogenesis in Muscovy ducks

1. Calcium (Ca) is essential for avian embryonic bone mineralisation, yet its metabolic dynamics during duck embryogenesis remain unclear. This study investigated Ca mobilisation in Muscovy duck embryos.2. Eggshell (ES) and yolk samples were collected from embryonic day (ED) 16 to ED31 for analysis of ES physical properties (thickness, strength, mass ratio) and Ca levels. Serum, yolk sac membrane (YSM) and liver tissues were collected from ED16 to the day of hatch (DOH) to assess serum biochemical parameters and relative mRNA expression of genes associated with Ca transport (PLCG1, PRKCA, CALM1) and absorption (CALB1, ARNT, EP300).3. Results showed ES quality and Ca levels decreased (p < 0.01) linearly with increasing incubation days. Yolk Ca levels decreased (p < 0.01) linearly and quadratically, reaching a minimum on ED25. Serum Ca levels and alkaline phosphatase (ALP) activity increased (p < 0.01) linearly and quadratically during ED16-DOH and achieved a plateau during ED28-DOH. Expression of Ca-related genes in YSM and liver increased quadratically (p < 0.01), peaking during ED25-28.4. In conclusion, ES quality declined with reduced Ca levels during embryogenesis. Concurrently, yolk Ca levels, along with serum Ca and ALP levels, increased significantly during ED25-28, indicating peak embryonic Ca mobilisation during this period. Additionally, relative mRNA expression of Ca mobilisation-related genes in the YSM and liver exhibited a similar increasing trend. This suggested enhanced Ca mobilisation during this phase to support bone mineralisation and growth in duck embryos.