Which gene was introduced in the first transgenic cow?

Human Alpha-lactalbumin

The gene introduced in the first transgenic cow was:

☀ Human Alpha-lactalbumin

The first transgenic cow, named Rosie, was created by introducing a human alpha-lactalbumin gene into the cow's genome. This genetic modification allowed Rosie to produce milk with higher levels of this protein, which is normally found in human breast milk and is important for milk production and composition.

In 1997, the first transgenic cow, Rosie, produced human protein-enriched milk (2.4 grams per litre). The milk contained the human alpha-lactalbumin and was nutritionally a more balanced product for human babies than natural cow-milk.