Symptoms of a Dog in Heat

A pair of Pomeranian dogs

If you own an unspayed female, knowing the symptoms of heat can be very important to managing her reproductive cycle. Learning the stages of the cycle will allow you to recognize symptoms like personality changes, appetite changes, and more as symptoms of a dog in heat rather than something that requires a visit to the vet. It could also help you prevent having new puppies on your hands when you didn't plan for them, and allow you to plan for puppies when you do want them.

Recognizing the Symptoms of a Dog in Heat

To better understand the many symptoms of the dog heat cycle, it's best to break down the various stages of the average 21 day heat cycle. Doing so can help you determine which part of the cycle your bitch is in, and it can also help in planning or preventing a litter. Keep in mind that the 21 day cycle is just a guideline and every dog is different. According to, a heat cycle can be anywhere from seven days to four weeks long. The heat cycle usually occurs twice a year, though some dogs will go more or less than six months between cycles.

Week One: Proestrus

Proestrus is the term used to describe the initial portion of the heat cycle. This period can last from seven to ten days, but many bitches typically experience about nine days in proestrus. According to, the first sign that the dog is going into heat is the swelling of the vulva. However, the swelling as it relates to the bleeding isn't completely predictable. The vulva could swell one week to a day before the bleeding starts.

During this time, you'll notice many but perhaps not all of the following symptoms of a dog in heat.

  • A personality change: Changes can range from quite mild to more severe. Sometimes a bitch will become more affectionate and clingy with her owner, other times she may seem a bit standoffish or grumpy. Some bitches act directly in opposition to their usual character, while others simply augment their natural personality.
    Dog's personality
  • Appetite changes: It's not unusual for a bitch to go off her food a bit during this first week of the estrus cycle, although more rarely a bitch becomes hungrier to the point of raiding the trash bin for discarded leftovers. Whatever the change is, taking note of it can be a significant clue that the heat cycle has begun.
    No appetite
  • Swelling of the vulva: The amount of vulva swelling varies from one bitch to the next. Some dogs swell ever so slightly, while others swell quite a lot. As the swelling progresses, it is not only noticeable from the vulva itself, but can also be seen trailing up to the pelvic opening just below the anus.
  • Bloody discharge from the vulva: The amount of bleeding also varies, but typically bleeding is light during the first few days and grows a bit heavier mid-week.
  • Tail tucking: This is a tendency to guard the vulva, either by tucking the tail between the leg or sitting down whenever another dog approaches the immediate area.
    Tail tucking

Week Two: Estrus

The onset of estrus marks the fertile portion in the heat cycle where the ovaries begin to release eggs for fertilization. During this period, symptoms include:

  • Lightened discharge: Previously bright red, the discharge now lightens to a pinkish-tan stain.
  • Softening of the vulva: Initial swelling subsides just enough to make the vulva soften enough for penetration.
  • Tail flagging and flirting: Whereas a bitch may previously have tucked her tail to fend off a male's advances, she now begins to behave flirtatiously. This can include inviting the male to mount by turning her rear toward him and holding the tail high and out of the way. She will fan it lightly to make sure he catches her scent. If conditions are truly right, a full mating may take place.
    Tail flagging and flirting

Week Three: Diestrus

As diestrus takes over, the fertile portion of the heat cycle comes to an end.

Signs of the end of the cycle include:

Gradual disappearance of vulva swelling: Most of the swelling is gone within one week's time, but the vulva may remain slightly enlarged after the first heat cycle has taken place.

Cessation of flirting: Whether bred or not, the bitch now lacks the conditions to mate and is no longer interested in flirting.

Cessation of flirting

Gradual cessation of discharge: The pinkish-tan discharge of estrus once again turns red, but now tapers off over the course of the final week.

Diestrus can be extended to encompass the 63-day period of the average canine pregnancy if a breeding was successful.

The Resting Stage: Anestrus

If no pregnancy results from a breeding during the heat cycle, the bitch goes back into anestrus. This is the five to eleven month period of inactivity that eventually cycles back into proestrus to begin the cycle anew.

Pay Attention to the Signs

Paying attention to the symptoms when your dog goes in heat will allow you to prepare for puppies or prevent mating from taking place. Understanding and timing the cycle is imperative if you have a dog that hasn't been spayed.

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Symptoms of a Dog in Heat