Has your female dog started her first heat cycle?
This is an exciting time. Your puppy has started adolescence, and she's finally growing up.
However, keep in mind that, at 6-15 months of age, your dog is still a puppy. If you plan on breeding your dog, the AKC recommends waiting until she is fully mature to do so.
If you do not plan on breeding your dog, you'll only need to worry about keeping her away from males while she is in heat. Learn the phases of your female dog's heat cycle so you'll know what to expect, and how to keep her safe.

Your Female Dog's Heat Cycle

The heat cycle has four phases: proestrus, estrus, diestrus and anestrus.

Proestrus
Proestrus is the first phase of your dog's heat cycle. Her vulva will become swollen, and she'll have bloody discharge. You may want to use disposable doggy diapers or washable underwear to keep her from making stains around your home. At this time, your dog will attract males who may attempt to mate with her, but she will usually not be receptive to them. Even so, you'll need to keep her away from males if you do not want her to have a litter. On average, proestrus lasts between 7 and 10 days.

Estrus
Estrus is the second phase of your dog's heat cycle - the mating phase. Her vulva will still be swollen, but her discharge will lighten in color. It'll go from red to pinkish to a pale yellowish color. You may still need to use diapers or underwear to prevent staining on your floor, furniture and bedding. When your dog is in estrus, she will become receptive to males.
Remember, just because your dog is no longer bleeding, does not mean that she can no longer become pregnant. Quite the opposite - she's much more likely to let a male mate with her immediately after the bloody discharge stops. If you have a male dog that is not neutered, use crates and/or gates to separate them. On average, estrus lasts between 5 and 10 days.

Diestrus
Diestrus is the third phase of your dog's heat cycle. This is the resting phase. At this time, she is either pregnant, or her body is returning to normal. She will no longer attract males, nor will she be receptive to them. You can safely let your female and male dogs spend time together again without risking an unwanted pregnancy. Diestrus lasts 10 to 140 days.

During estrus, and until diestrus, your dog's cervix is open, which can leave her vulnerable to a serious uterine infection called pyometra. If you notice any symptoms like increased drinking and urination, fever, vomiting or unusual discharge, particularly after your dog has been in heat, seek emergency veterinary care.

Anestrus
Anestrus is the fourth phase of your dog's heat cycle. This is the time period between diestrus and the beginning of her next heat. Dogs typically go into heat twice per year, so anestrus lasts approximately six months.

How Long Do I Have To Keep My Female Dog Separate From Males?

Though bloody discharge is a visible indicator of the start of your female's heat cycle, it is more difficult to determine when her fertile days have passed. To be on the safe side, do not allow her to encounter any unfixed males for 21-25 days after the first sign of bleeding.