Vitamin D is produced naturally in the body when exposed to the ultra violet rays from the sun, and its main function is to maintain normal blood levels of calcium, and phosphorus. Lack of vitamin D can cause soft egg shells, and brittle, or thin bones in fowl. Vitamin D also helps keep your birds immune system strong, and can affect their over all growth, and development. Extreme cases of vitamin D deficiency can even lead to diseases like Rickets.
Sources
The best way to keep normal levels of vitamin D in you fowl's system is exposure to sunlight, but if you need to supplement, you can get it from the following sources.
- Fish (tuna, salmon, sardines, mackerel)
- Boiled egg yolk
- Liver
- Water soluble vitamin supplements