Abstract: The present invention provides a modified nucleic acid for expressing bovine lactoferricin (LFB) in algae, which consists of SEQ ID NO: 3. The present invention also provides a method of producing a foreign desired gene product in algae, comprising: (a) weakening or removing cell wall of the algae by a protein enzyme solution to make algae become suitable for gene transfer; (b) transferring a foreign gene encoding the desired gene product into the algae; and (c) expressing the foreign gene to produce the desired gene product. The present invention further provides a feed composition comprising a transgenic algae or its offspring, wherein the cell wall of said transgenic algae is weakened or removed by a protein enzyme solution.