everyone has a different answer because it varies from one dog to another. In general, the heat cycle lasts about 21 days, but most people keep males away from 28 days of onset of bleeding to be on the safe side.
Also in general, a female dog will go into heat twice a year, and around 6 months apart. Again this will vary from one dog to another. I know the basenji only goes into heat once a year.
Do they bleed the entire 28 days? :| Mine is in heat for the first time right now.. not because I intend to breed her, but because she's an inside dog.. and I live in an apartment. The only time she is outside is while she's attended. So there will be no possibility of "accidental" breeding. I chose to do this, because.. if there's no possibility of her getting pregnant.. there's no reason to get her fix and risk death.
Halosfire, if you don't intend to breed her, I would get her spayed. There is a risk of cancer in females that arent spayed. Just wasn't sure if you knew that. And there are also a couple other health problems that can be completely avoided by getting her spayed. Ha, I have a brochure right in front of me from the vet (sorry I found it funny, didn't even know it was here) it says and I quote "eliminates females chances of developing uterine infections and reduces the possibility that she might develop mammary cancer".
Yes, I am aware of the risk of cancer.. but it's only a "possibility" just as getting her fixed resulting in death is a "possibility". I'm just not ready to willingly put her under, and risk the chance of losing her. I just can't make myself do it. :|
Halosfire - Is she a breed that has specific problems with anesthesia? If not, you might want to look at having her spayed. I know it's hard to put them under, I had all three of my girls spayed on the same day. My vet used Iso (Scout can give you a better idea) and not one problem. Pyometra (sp??) can sneak in and put your girl in pretty bad shape before you even know she has it. She would then have to have an emergency spay. Spaying is much more risky if your girl isn't in good health. Just some things to consider. :)