In the U.S. genetically modified chickens are not legal for meat production. The FDA recently approved a genetically modified chicken to be able to produce a certain drug from its egg whites. The FDA had previously approved genetically modified goats for the production of a drug in their milk.Those methods are forbidden in animals.
Although many people claim that hybrids like the white meat birds, the white leghorns and the sex links are GMO.
I don't believe it.
https://www.theverge.com/2015/12/9/9879678/gmo-chicken-transgenic-fda-approved-kanuma-drug-eggs
While genetic modification is not legal for meat production, genetic modification research on animals is not prohibited.