Super-doses of dietary vitamin D3 intake in aged laying hens illustrates limitation of 24,25-dihydroxycholecalciferol conversion

Abstract

ABSRACTBackgroundHumans take vitamin D supplements to reduce risk of vitamin D deficiency and reduce the risk of osteoporosis. However, it is unclear how dietary super-doses (10,000x greater than requirement) can affect vitamin D status in aged animals. Aged laying hens could be a model to compare with women in peri- or postmenopausal stages of life. The hens’ bone health is physiologically taxed from egg production and they are highly susceptible to osteoporosis.ObjectiveWe investigated dietary super-dose impacts of cholecalciferol (vitamin D3) on vitamin D status in aged laying hens in production.MethodsForty-eight 68 wk old Hy-Line Brown laying hens were individually housed in cages with eight hens per dietary treatment for eleven weeks. Hens were randomly assigned to one of six groups of dietary vitamin D3 supplementation and fed ad libitum. Supplementation levels were 400, 800, 7,400, 14,000, 20,000, and 36,000 IU D3/kg of feed. At termination of the study, all hens were euthanized and we collected tissue samples and their feces. Tissue calcium, plasma and egg yolk vitamin D metabolites, and gene expression levels were measured.ResultsWe observed that increasing dietary vitamin D3 increased plasma vitamin D3, 25-hydroxycholecalciferol, and 24,25-dihydroxycholecalciferol concentrations (p < 0.0001 for all 3 metabolites). Also, egg yolk vitamin D3 and 25-hydroxycholecalciferol showed a similar effect like plasma vitamin D metabolites (p < 0.0001 for both metabolites). We also observed super-dose fed hens had decreased kidney 24-hydroxylase expression (p = 0.0006).ConclusionsDietary super-doses of vitamin D3 led to greater plasma and egg yolk vitamin D levels to show that aged laying hens can deposit excess vitamin D in egg yolk. We suggest future research should explore how 24-hydroxylation mechanisms are affected by vitamin D supplementation. Further understanding of 24-hydroxylation can help ascertain ways to reduce risk of vitamin D toxicity.