There's got to be a "cock diesel" joke in there somewhere.
Seriously though, it's just a way to skirt laws. I don't even think the cock fighting circuit uses tablets to strengthen their birds.
My friend attends and has teams that compete in the biggest Derbys in Mexico (that's what they call the cockfighting events). The birds are on test, winstrol, and ephedrine. I have attended small derbys. Very festive.
-The birds fight in weight classes
-Different "knives" are used in different fights
-Big events have legit corporate sponsors
-Cash prize money often tops $100,000 in bigger derbys
Some examples of different knives: