The major storage and circulatory form of vitamin D is:-

Cholecalciferol is first hydroxylated at 25th position to 25-hydroxycholecalciferol (25-OH o3) bv a specific hydroxylase present in  liver. 25-OH D3 is the major storage and circulatory form of vitamin D. Reference: Satyanarayana- Biochemistry, 3rd edition, pg-125