those bulls/cows are not on hormones. They are truly natty.
Just selectively bred over hundred of years... Only breeding cows/bulls which showed musclemass above normal. In that pursuit they ended up beeding cows/bulls lacking the myostatin gene. The gene which inhibits muscular growth beyond "normal" levels.
There are humans lacking this gene(very rare) that also shows muscle mass beyond normal without even training. I'm sure there are more cases than we know where we will just deem them not natty. Sports and probably alot of olympic games athletes probably has their fair share of athletes rising to the top due to lacking this gene