title: Free-range farming: a natural alternative to produce vitamin D-enriched eggs.
abstract: OBJECTIVE
  Food-based strategies need to be developed to improve the vitamin D status of individuals. Recent studies identified ultraviolet B irradiation as an efficient method to enrich mushrooms and eggs with vitamin D. The aim of this study was to determine whether free-range farming of hens could provide a valuable method to produce vitamin D-enriched eggs.
  
  
  METHODS
  Laying hens were randomly assigned to three groups of 33 to 34 animals each, and were kept either indoors (indoor group), outdoors (outdoor group), or with an indoor/outdoor option (indoor/outdoor group) over 4 wk.
  
  
  RESULTS
  The study shows that the vitamin D3 content of egg yolk was three- to fourfold higher in the groups that were exposed to sunlight (outdoor and indoor/outdoor groups) compared with the indoor group (P < 0.001). Egg yolk from the outdoor group revealed the highest vitamin D3 content, which averaged 14.3 μg/100 g dry matter (DM), followed by that from the indoor/outdoor group (11.3 μg/100 g DM). Yolk from indoor eggs contained only 3.8 μg vitamin D/100 g DM. The 25-hydroxyvitamin D (25[OH]D3) content of egg yolk was also influenced by sunlight exposure, although less pronounced than the vitamin D content (P < 0.05). In contrast, free-range eggs randomly acquired from supermarkets had relatively low vitamin D contents.
  
  
  CONCLUSIONS
  Free-range farming offers an efficient alternative to fortify eggs with vitamin D, provided that farming conditions are sufficiently attractive for hens to range outside.
authors.affiliation: Institute of Agricultural and Nutritional Sciences, Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Kühn
authors.affiliation: Institute of Agricultural and Nutritional Sciences, Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Schutkowski
authors.affiliation: Institute of Agricultural and Nutritional Sciences, Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Kluge
authors.affiliation: Institute of Agricultural and Nutritional Sciences, Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Hirche
authors.affiliation: Institute of Agricultural and Nutritional Sciences, Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany. Electronic address: Gabriele.stangl@landw.uni-halle.de.
authors.forename: Gabriele I
authors.initials: GI
authors.lastname: Stangl
mesh_terms: D000821:Animal Feed; D000822:Animal Husbandry / Q000379:methods*; D000818:Animals; D002645:Chickens; D002762:Cholecalciferol / Q000378:metabolism*; D004032:Diet; D004530:Egg Yolk / Q000378:metabolism*; D004531:Eggs / Q000032:analysis*; D005260:Female; D006801:Humans; D009753:Nutritive Value; D011897:Random Allocation; D013472:Sunlight; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D014807:Vitamin D; D002762:Cholecalciferol; C104450:25-hydroxyvitamin D
keywords: Eggs; Free-range farming; Hen; Natural sunlight; Vitamin D