Catch dog help needed.

If your lucks like mine, he'll kill or breed her, either way bad.
I'd just let him settle in good and get to know the surroundings and his new "home" for a week or so.
Until I was 100% positive, I would not "let her out" if you mean loose. You need to be able to control the situation, should things go badly.
The best way for me is to keep one on a good chain staked out and lead the other in circles, gradually gettin closer and closer.
When they get just close enough to smell each other, momentarily pause and let them sniff, then lead one away.
This can be done several times if a fight does not start. Be ready to pull on the lead to seperate them just in case.
Then I'd slowly begin to introduce him to newer stuff, like the trash breaking.
Even if you have no intentions of turning him out around cattle, it is good practice to have him trash broke, if possible.
If he ever got loose and the cows came close, that's a wreck waiting to happen.

Just mu $.02.