Believe me, I don't envy you the task of keeping them separated! :)
When intact males are around a female in season they can be VERY persistent and VERY resourceful in terms of finding a way to get to her. Losing track of one of them for a nanosecond can result in an unwanted breeding, and the bad thing about it is if she allows one of them to breed her and they manage to achieve a tie (where the two dogs become "stuck" together), she will almost ALWAYS turn up pregnant. It's very unusual for a female to allow herself to be bred and not get pregnant. If only people who wanted children badly were able to do this! LOL I know of someone who had a female get pregnant on the 24th day of her heat cycle, so that 21 day rule is definitely not hard and fast. The swelling is the only sure way to tell.
Ghilly
Thank you for that information it has help us a great deal understanding how long we'll have to keep our male dogs away from our daughters female dogs.
What a chore!!!! Pray :)
Ruthie
The average heat cycle lasts 21 days, but some of them don't go quite as long and some of them go a little longer. The key is to watch the swelling of the vulva. Don't relax and think it's OK to let her get around male dogs until all of that swelling is gone, because as long as she's even a little swollen, there's a chance she'll allow them to breed her.
Unless you're going to breed her, wait until about a month or so after all the swelling has gone and then have her spayed. It takes about 30 days for the body to return to normal with regard to the blood vessels around the uterus not being engorged with blood with the plans to facilitate a pregnancy, and you want those vessels to go down so that there's not an increased chance of bleeding during the surgery. It makes the surgery a lot less risky.
Ghilly