Your question doesn't make sense.
All bulls are uncastrated males. Castrated males are called steers.
Females are cows...or if they haven't had a calf, they're called heifers.
If you're trying to keep a bull from breeding a cow, you'll need to separate them with a good barrier of some sort. Bulls and cows will go through fences to get together to breed.
If you have a set of just bulls and they're mounting each other, that's a dominance issue,not a breeding issue. It doesn't hurt anything usually. It's just how they work out who's the top guy in the bull pen. Once they work that out, they'll mostly ignore each other.
However, if one is quite a bit smaller, the larger bulls could pick on him and actually injure his back. You need to see if one is being mounted more than others and maybe separate him from the other bulls.