Dietary calcium deficiency in laying ducks impairs eggshell quality by suppressing the process of shell biomineralization

Abstract

The objective of this study was to determine the effects of dietary calcium deficiency on the process of shell formation. Four hundred and fifty female ducks (Anas platyrhynchos) of 22 wk were randomly assigned to 3 groups. Ducks were fed one of two calcium-deficient diets (containing 1.8% or 0.38% calcium, respectively) or a calcium-adequate control diet (containing 3.6% calcium) for 67 d (depletion period), and then ducks of the 3 groups were fed a calcium-adequate diet for an additional 67 d (repletion period). As compared with the calcium-adequate control, the average shell thickness, egg shell weight, breaking strength, mammillae density and mammillary knob thickness of shell from ducks that consumed the diet with 0.38% calcium was significantly decreased (P<0.05) during the depletion period, accompanied by reduced quality of shell and tibia. The mRNA expression of both secreted phosphoprotein 1 (SPP1) and carbonic anhydrase 2 (CA2) in uterus were decreased after feeding calcium-deficient diets (1.8% or 0.38% calcium). Transcripts of calbindin 1 (CALB1), an important protein responsible for calcium transport, and matrix protein gene ovocalyxin-32 (OCX-32) and ovocleidin-116 (OC-116) were reduced in the ducks fed 0.38% calcium but not the 1.8% calcium. Plasma estradiol concentration was decreased by both of the calcium-deficient diets (P<0.05). The impaired shell quality and suppressed functional proteins involved in shell formation could be reversed by repletion of dietary calcium. The results of the present study suggest that dietary calcium deficiency negatively affects the eggshell quality and eggshell microarchitecture probably through suppressing the process of shell biomineralization.