Provided is a method or producing a transgenic animal having modified resistance to a disease. One embodiment of the method is performed by introducing a retrovirus into a cell of the animal or a cell which is capable of producing the animal, wherein the retrovirus comprises a polynucleotide sequence which encodes and is capable of expressing a protein which modifies the disease resistance of the animal, and wherein when the cell is a cell which is capable of producing the animal, producing the animal from the cell.