In Belgium we have cows specifically breaded for meat, which are called "dikbil" =(fatbutt). It's extremely unnatural, so I'm very afraid what kind of monstrosity the industry can come up with when using gene manipulation. https://www.google.com/search?q=dikbil
It's muscular hyperplasia obtained from inbreeding: https://en.wikipedia.org/wiki/Belgian_Blue
They did the same thing in Piedmont, Italy: https://en.wikipedia.org/wiki/Piedmontese_cattle