In vitro meat would be great. Yet you still need to introduce a small number of pathogens to improve your fitness (your body needs to fight small battles all the time to keep in the top shape). Sanitized stuff brings you allergy and other fun, like inability to adapt to changing environment.
Should be solvable by frequently swapping out the cell sources for the breeding, using fresh samples from live farm animals (tested for harmful pathogens first, of course).
If you don't have all of the nasty digestion bits of a bird, you lost a lot of the nasty disease bits.
If you only have the meat parts of the bird, you don't waste any growth resources on non-saleable parts of the bird.