Parathyroid hormone and eggshell calcification in Japanese quail

Area of Science:

• Avian physiology
• Endocrinology
• Calcium metabolism

Background:

• Eggshell calcification is crucial for avian reproduction.
• Parathyroid hormone (PTH) regulates calcium homeostasis.
• The specific role of PTH in avian eggshell formation requires further elucidation.

Purpose of the Study:

• To investigate the effect of parathyroid hormone (PTH) on eggshell calcification in Japanese quail.
• To determine the impact of PTH administration timing on calcium deposition and shell characteristics.

Main Methods:

• Japanese quail were injected with parathyroid extract (PTE) or purified PTH at different times relative to oviposition (2-6 h vs. 12-16 h).
• Calcium-45 (45Ca) was used to trace bone calcium mobilization and deposition into the eggshell.
• Eggshell weight per unit area and calcium content per unit area were measured.

Main Results:

• Injections within 2-6 h post-oviposition significantly increased 45Ca deposition into the eggshell, indicating enhanced bone calcium mobilization.
• Simultaneously, eggshell weight per unit area and calcium content per unit area significantly decreased.
• Injections 12-16 h post-oviposition did not produce these effects, suggesting a time-dependent action.

Conclusions:

• PTH administration shortly after oviposition mobilizes bone calcium for eggshell formation but paradoxically reduces shell weight and density.
• PTH may act directly or indirectly on the avian oviduct to limit calcification.
• The lack of effect in later-treated birds might be due to saturated endogenous PTH receptor levels.