Transgenic animals are those animals whose genomes are modify or altered by transferring the genes from another animals species or breeds. It is also defined as the insertion of foreign gene into an genome. The most common method for producing transgenic animals is microinjection, which involves several steps. First, the DNA containing the transgene is identified and cloned into several copies. This DNA is then inserted into a host animal, such as a pig, cow, or sheep, which is stimulated to superovulate so that eggs can be collected.

The collected eggs are fertilized in vitro, and a fine needle is used to inject the DNA solution containing the transgene into the male pronucleus of a fertilized egg before it fuses with the female pronucleus. The transgenic embryos are allowed to grow in cell culture before being implanted into the uterus of a surrogate mother, where they will develop fully. The offspring are then tested to determine if they have inherited the transgene.

Microinjection has the disadvantage of a low success rate. Recently, the CRISPR-Cas9 technique has become a more widely used method for producing transgenic animals due to its higher efficiency.