Answer:
Producing transgenic animals has practical advantages, such as using less than half of experimental animals for the production of an envelope.
Explanation:
Currently it is only possible to add genes, the transgenic sheep that exist are found to produce human proteins. However, it is convenient for some proteins to remove endogenous proteins from milk. For example, for human serum albumin.
There is a high demand for some human proteins for the treatment of various diseases. Small quantities can be produced in cell cultures but the cost is very high. Higher amounts can be made by bacteria or yeasts, but proteins are difficult to purify and that is why some of the advantages of having transgenic animals is the amount of protein produced.