Dietary Super-Doses of Cholecalciferol Fed to Aged Laying Hens Illustrates Limitation of 24,25-Dihydroxycholecalciferol Conversion.

BACKGROUND

Older humans taking high concentrations of vitamin D supplementation for a prolonged time may be at risk of vitamin D toxicity. It is unclear how dietary super-doses (10,000 times greater than the requirement) can affect vitamin D status in aged animals. Aged laying hens could be a model to compare vitamin D supplementation effects with women in peri- or postmenopausal stages of life.

OBJECTIVES

We investigated the dietary super-dose impacts of cholecalciferol (vitamin D) on vitamin D status in aged laying hens in production.

METHODS

Forty-eight 68-wk-old Hy-Line Brown laying hens were individually housed in cages with 8 hens per dietary treatment for 11 wk. Hens were randomly assigned to 1 of 6 treatment groups of dietary vitamin D supplementation and consumed . Supplementation concentrations were 400, 800, 7400, 14,000, 20,000, and 36,000 IU D/kg of feed. At the end of the study, all hens were sacrificed, and tissue samples and feces were collected. Plasma and egg yolk vitamin D metabolites, calcium and phosphorus composition of eggshells, ileal digesta, and feces were measured. Duodenal, ileal, liver, and kidney gene expression levels were also measured.

RESULTS

We observed that increasing dietary vitamin D increased plasma vitamin D and egg yolk vitamin D ( < 0.0001 for both sites). We also observed an increase in plasma 24,25-dihydroxycholecalciferol as dietary vitamin D concentrations increased ( < 0.0001). The plasma 25-hydroxycholecalciferol:24,25-dihydroxycholecalciferol ratio exhibited an asymptotic relationship starting at the 14,000 IU/kg D treatment.

CONCLUSIONS

Dietary super-doses of vitamin D led to greater plasma and egg yolk vitamin D concentrations, which shows 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 the risk of vitamin D toxicity.