Super Cow

Incredibly, this picture is not photoshopped. This type of cow is known as a Belgian Blue. The hyper-muscular physique is due to a condition known as 'double-muscling'. Double-muscling is the result of a mutation in the mysostatin gene of the animal, which leads to the absence of functional myostatin, the protein that inhibits muscle development.

In the absence of functional mysotatin, the phenotype develops a condition known as hyplerplasia which is characterized by an excessive number of muscle fibers. While the animal demonstrating this trait is the result of genetic mutation and decades of selective breeding, it is not technically the result of 'genetic engineering' in the modern sense of the term (ie. manually adding new DNA to an organism's genome)