Plasma vitamin A composition and retinol-binding protein concentration during egg formation in laying hens.

Blood plasma vitamin A composition (retinol, retinyl ester) and retinol-binding protein (RBP) were determined in three phases (empty; soft- and hard egg) of the egg formation period in laying hens. The retinyl ester level remained in the range of 6 to 11% of the total plasma vitamin A concentration during egg formation. The retinol and RBP increased significantly during the time of soft period. The molar ratio between retinol and RBP ranged between 0.72-0.77. The increase of retinol and RBP may be caused by the sexual steroid effect for satisfying the retinoid needs of the ovarium and shell gland (avian uterus).