Enables vitamin D3 25-hydroxylase activity. Acts upstream of or within vitamin D metabolic process. Predicted to be located in endoplasmic reticulum and membrane. Predicted to be active in cytoplasm and intracellular membrane-bounded organelle. Is expressed in embryo; liver; and testis. Human ortholog(s) of this gene implicated in type 1 diabetes mellitus and vitamin D-dependent rickets type 1B. Orthologous to human CYP2R1 (cytochrome P450 family 2 subfamily R member 1). [provided by Alliance of Genome Resources, Apr 2022]