The site of 7-dehydrocholesterol ultraviolet photolysis in domestic fowls.

The site of the photolytic reaction leading to Vitamin D3 in fowls integument has been investigated by histochemical and biochemical analysis. The Vitamin D3 precursor, 7-dehydrocholesterol, is synthetized and stored mainly in the uropygial gland and in the same localization several amount of Vitamin D3 may be biochemically detected. 7-dehydrocholesterol and Vitamin D3 are also present although in a lesser amount in the unfeathered skin of the legs. Photolytic conversion of the Vitamin D3 precursor of uropygial origin may occur also on the dorsal feathers.