In the wake of Wendy the Whopper Whippet, Aaron sent me a link to a few more over-muscled critters.
I found the cows on the site to be particularly noteworthy. The sad thing here is that these cows are often bred to isolate the gene that hinders the production of myostatin, resulting in the large, lean muscle mass you see here.
Some advocate eliminating these strains of cattle (the belgian blue below, in particular). I don't know about that, but I do intend to ask the next restaurant that serves me a burger if they serve meat from cattle that have myostatin problems. I'm sure the server will know the answer.
Photos from: Who-Sucks.com