Dietary supplementation with calcitriol or quercetin improved eggshell and bone quality by modulating calcium metabolism.

This study was aimed to investigate the effects of dietary calcitriol or quercetin supplementation on eggshell and bone quality of laying hens. In trial 1, 72 Hy-Line Brown layers (80-week-old) with weak-shelled strength (25 to 30 N) were assigned into 4 dietary treatments with 6 replicates of 3 birds and fed a basal diet (4% calcium level) or basal diets supplemented with 0.5% calcium, 5 μg/kg calcitriol or 500 mg/kg quercetin for 4 weeks. In trial 2, 360 Hy-Line Brown layers (60-week-old) were divided into 3 groups with 8 replicates of 15 birds: control group (basal diet), calcitriol group (basal diet + 5 μg/kg calcitriol), and quercetin group (basal diet + 500 mg/kg quercetin). This trial lasted for 12 weeks. The results showed that dietary calcitriol or quercetin improved eggshell quality in both trials ( < 0.05). In trial 2, compared with the control group, both calcitriol and quercetin supplementations improved femoral bone quality, calcium retention of hens and calcium content in uterine fluid at 18.5 h post-oviposition (PO) ( < 0.05), along with enhancing uterine morphology. Compared to the control group, supplemental calcitriol or quercetin up-regulated the relative mRNA expression levels of uterine transient receptor potential cation channel, subfamily V, member 6 () at 8.5 h PO and plasma membrane calcium-ATPase (), vitamin D receptor (), estrogen receptor alpha () at 18.5 h PO ( < 0.05), but down-regulated the uterine caspase 3 () relative mRNA expression level at 8.5 h PO ( < 0.05). Meanwhile, the femoral relative mRNA expression levels of tartrate-resistant acid phosphatase () (up-regulated at 8.5 and 18.5 h PO) and alkaline phosphatase () (up-regulated at 8.5 h PO but down-regulated at 18.5 h PO) were also affected by calcitriol or quercetin supplementation ( < 0.05). Compared to the calcitriol, quercetin increased hen-day egg production and femoral medullary bone volume/bone tissue volume but reduced femoral stiffness ( < 0.05), which were accompanied by increased relative mRNA expression levels of uterine , estrogen receptor beta () at 18.5 h PO ( < 0.05). Overall, both dietary calcitriol and quercetin could improve eggshell and bone quality by modulating calcium metabolism of aged layers. Compared to calcitriol, dietary quercetin up-regulated the expression of uterine calcium transporters, without affecting eggshell quality.