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Ontogeny and oestradiol dependence of vitamin D-binding protein blood levels in chickens
Insights
Chicken blood levels of 25-hydroxyvitamin D3-binding protein (DBP) increase significantly after hatching and before sexual maturity. These changes in DBP correlate with 1,25-(OH)2D3 levels, particularly influenced by oestrogen in laying hens.
Area of Science:
- Avian physiology
- Endocrinology
- Nutritional biochemistry
Background:
- 25-hydroxyvitamin D3-binding protein (DBP) plays a crucial role in vitamin D transport and metabolism.
- Understanding DBP dynamics is essential for avian health and productivity, especially concerning calcium and eggshell formation.
- Limited data exists on DBP ontogeny and its hormonal regulation in chickens.
Purpose of the Study:
- To investigate the developmental changes in chicken plasma DBP concentrations from embryonic stages to sexual maturity.
- To explore the relationship between DBP levels, vitamin D status, and reproductive hormones (oestradiol, progesterone, testosterone).
- To determine the influence of egg formation and 1,25-(OH)2D3 on DBP levels.
Main Methods:
- Immunodiffusion assay was used to quantify DBP concentrations in chicken blood plasma.
- Blood samples were collected from chickens at various developmental stages, including embryonic, post-hatching, and pre-sexual maturity.
- Hormonal treatments (oestradiol, progesterone, testosterone) and experimental manipulation of egg formation were employed.
Main Results:
- DBP levels were low in chick embryos and increased significantly post-hatching, with a notable surge before sexual maturity.
- DBP concentrations showed a strong positive correlation with plasma oestradiol levels, particularly in laying and moulting hens.
- Exogenous oestradiol administration induced a significant increase in DBP in immature chickens, while progesterone and testosterone had no effect.
- Eggshell formation suppression did not alter DBP levels, but DBP and 1,25-(OH)2D3 were elevated in hens laying shell-less eggs.
Conclusions:
- Chicken plasma DBP levels exhibit distinct developmental patterns, influenced by reproductive status and hormonal milieu.
- Oestrogen plays a key role in regulating DBP synthesis in chickens, suggesting a link between reproductive endocrinology and vitamin D transport.
- The findings suggest a complex interplay between DBP, 1,25-(OH)2D3, and reproductive hormones in avian physiology, particularly during egg production.
Abstract:
The concentration of 25-hydroxyvitamin D3-binding protein (DBP) was measured, by immunodiffusion, in the blood of chickens from embryonic stages to sexual maturity. Low levels of DBP and 1,25-(OH)2D3 were detectable in the blood of chick embryos from the 12th and 17th day of incubation respectively and stayed at the same low levels until hatching. The blood concentration of DBP doubled between the 1st and 5th days of life, then increased slowly and reached the mean level of the adult male at 7-8 weeks of age. The concentration of DBP was independent of vitamin D status in growing chickens. A large increase was observed in DBP blood levels in hens just before sexual maturity. This change, and those observed in moulting hens, followed the variations in plasma concentrations of oestradiol more closely than those of progesterone or testosterone. Moreover, a large increase in plasma DBP levels was induced in immature chickens by oestradiol (0.5 mg/day), but not by testosterone or progesterone. Finally, the experimental suppression of egg shell formation and the associated decrease in 1,25-(OH)2D3 plasma levels had no effect on plasma DBP concentrations. However, 1,25-(OH)2D3 and DBP levels were higher in hens laying shell-less eggs than in immature pullets. The increases in DBP levels at hatching, in immature pullets treated with oestrogens, in hens laying uncalcified eggs and at the onset of egg production were associated with increases in 1,25-(OH)2D3, suggesting a relationship between the levels of DBP and 1,25-(OH)2D3 in the blood.