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Do dogs have periods? All about female dogs’ heat cycles

Dog in heat

Reviewed by: Dr. David Tittle,BVetMed, CertVA, GPCert(WVA&CPM), MRCVS

Like most mammals, unspayed female dogs experience an estrous cycle when they reach sexual maturity. A dog’s reproductive cycle, however, looks a lot different than that of a human female. So, do dogs have periods? What do pet parents need to know about dog periods? 

Table of contents 

Do dogs have periods? 

Dogs, although they do ovulate, do not have menstrual periods like humans do. Female dogs have a reproductive or heat cycle, during which they become fertile and can become pregnant. Heat cycles are controlled by hormones, and marked by an increase in estrogen levels, then a sharp decrease in estrogen and finally, the releasing of eggs from their ovaries followed by an increase in progesterone. 

During heat or estrus, a female dog may have a bloody discharge from her vulva—similar to a human period or menstruation, but not caused by the shedding of the uterine lining. Instead, the bleeding is caused by a combination of blood, mucus, and other fluids that are released from the dog’s cervix. 

When do dogs go into heat? 

The timing of a dog’s heat cycle can vary depending on the individual dog and her breed, but most dogs will reach sexual maturity and have their first heat cycle between six and twelve months of age. 

Small breeds of dogs tend to have their first heat cycles earlier, around six months of age, while larger breeds may not have their first heat cycle until they are a year or even older. However, these are general guidelines and some individual dogs may have their first heat cycles at different ages.  

The timing of heat cycles can also be affected by factors such as overall health, nutrition, and environment. According to VCA Hospitals, delayed heat may be caused by a number of reasons, like malnutrition, excessive physical activity, medicines that meddles with fertility, or a lack of exposure to other females experiencing heat. Additionally, hormonal imbalances and genetic problems may also cause abnormal estrous cycles. 

How long do dog heat cycles last? 

The length of a dog’s estrus cycle can vary depending on the individual dog and her breed, but it typically lasts between 2-4 weeks. It is divided into several stages:

  1. Proestrus: 3-17 days, average 7 days 
  2. Estrus: 3-18 days, average 9 days 
  3. Diestrus: 58-68 days, average 60 days 
  4. Anestrus: 100-150 days 

A dog is said to be in heat when they are in the proestrus and estrus stages of their reproductive cycle. In total, bleeding during a dog’s heat cycle (proestrus and estrus stages) typically lasts 1-3 weeks. 

It’s important to note that not all dogs will have heat cycles that follow this exact timeline, and some may have cycles that are shorter or longer. Heat cycles can also be affected by health issues, so if you notice that your dog’s heat cycles are not following a normal pattern, it’s best to consult with a veterinarian to rule out any underlying health problems. 

Stages of dog heat 

As previously mentioned, a dog’s heat cycle, also known as the estrous cycle, is divided into four stages: 

  1. Proestrus: During this stage, the female dog’s vulva will start to swell and she will have a light, bloody discharge that becomes heavier. However, she is not yet fertile and cannot get pregnant. Hormones like estrogen are rising during this phase. Your dog may become more affectionate and clingy, but some dogs will get grumpy and stressed. During proestrus, male dogs are attracted to a female, but she is not receptive to them. While out on walks, you may notice that your pup tucks their tail and hides from male dogs, not wanting their attention. 
  2. Estrus: The second stage of the heat cycle is when the female dog is fertile and can get pregnant. The vulva will still be swollen and there will be a reddish-brown discharge, but both will start to reduce. Ovulation occurs during this phase and it’s characterized by a sudden drop in estrogen and an increase in progesterone. Pet owners will probably notice that your dog is more willing to accept male company, and you may notice male dogs giving them more attention because of the pheromones they’re releasing. Your pup may flirt with dogs by raising their tail and moving it to one side or the other (known as “flagging”) and raising their rear. 
  3. Diestrus: If the female dog has been bred and becomes pregnant, this is the stage where the pregnancy occurs. If she wasn’t bred, her body will be preparing to cycle again. Progesterone levels are high during this phase. At this stage, female dogs are no longer fertile or receptive to males. The vulva returns to normal size and discharge dries up. 
  4. Anestrus: The fourth stage is a period of inactivity or rest when the dog’s body is preparing for the next heat cycle. Hormones level return to normal during this phase. 

How often do dogs go into heat? 

Once they reach puberty and begin having estrus cycles, the frequency of a dog’s heat cycles can vary depending on the individual dog and her breed. The average time between cycles is about six to twelve months. But just like with human menstrual cycles, it can take a while for your dog to develop a regular cycle. Some breeds of dogs have cycles that occur less frequently, such as once a year or even less often. Other breeds may have cycles that occur more frequently, such as every four to six months. 

There are a few factors that go into how often your dog will go into heat. Small dogs tend to go into heat more often, but large breeds and older dogs may go longer stretches between heats. Age and overall health also can affect the frequency of heat cycles, and some breeds of dogs may have delayed cycles or stop having heat cycles once they reach certain age. 

Unlike humans, female dogs do not go into menopause. Once they reach puberty and begin having heat cycles, they will continue having a heat cycle their entire lives or until they are spayed. However, there may be a longer stretch of time between their heats as they age. 

Signs of dog heat 

There are several signs that can indicate that a female dog is in heat. If your dog sexually mature and is not spayed, monitor for heat symptoms, including: 

Physical signs: 

  • Swelling of the vulva: This is usually the first and most obvious sign that a female dog is in heat. The swelling may be accompanied by a slight discharge. 
  • Blood-tinged discharge: As the heat cycle progresses, the discharge may become more pronounced and may be tinged with blood. 

Behavioral cues: 

  • Increased irritability: Your dog may become moodier, potentially growling at people or other pets, particularly other unspayed female dogs. Their interest in human interactions may also change, either increasing or decreasing. 
  • Increased stress and restlessness: Some dogs may become stressed or agitated during heat. 
  • Roaming and escaping: Dogs in heat may show an increased interest in roaming or getting out of the yard to look for male dogs to mate with. 
  • Changes in appetite: Your dog may resist her food, become a pickier eater, or become more ravenous. 
  • Flagging: Female dogs in heat will often raise their tail and “flag” it to the side when they are ready to breed. 
  • Interest from male dogs: Female dogs in heat will emit pheromones that can be detected by male dogs from some distance away. Male dogs may become more interested in the female dog and may try to mount her. 

It’s important to note that not all female dogs will experience heat cycles in the same way. Some may have more visible signs, such as a heavier discharge, while others may have very little visible signs at all. 

What to do when female dog is in heat 

If your dog goes into heat, what should you do to keep her comfortable, safe, and healthy? 

  • Clean regularly — When a female dog goes into heat, you might find yourself having to clean up the bloody discharge. While dogs tend to clean themselves during their heat cycle, your dog may need some extra cleanup. Consider getting reusable or disposable doggie diapers and covering soft surfaces like rugs and furniture. Make sure you have cleaning supplies such as disinfectant wipes and stain remover stocked up. Cleaning blood stains promptly will help to avoid attracting other animals, including intact male dogs.  
  • Adjust your routines as needed — While in proestrus and estrus, your dog may need to be let out more regularly to urinate. Every dog is different! Some dogs may need more exercise while in heat to combat restless energy, but others may feel lethargic and need less exercise than usual. 
  • Keep your dog secure and away from unneutered male dogs — When a female dog is in heat, it is best to keep her separated from male dogs to prevent unwanted breeding. Female dogs in heat can also attract male dogs from the neighborhood, so it is important to keep her inside, walk only on leash, or in a securely fenced area during this time. Additionally, even contact with spayed or neutered dogs can result in hormone-related aggression. 
  • Give her as much (or as little) space as she wants — Let your dog tell you how much interaction she wants with you—let her come to you, otherwise, give her space. When a female dog is in heat, it can be helpful to spend more time and attention with her. This can be particularly effective if your female dog appears extra nervous or skittish while in heat. 
  • Make your dog comfortable — Make sure to provide her with a comfortable place to rest and provide plenty of food and water. 

With proper attention and tools, your dog’s heat cycle can be easy to manage. Schedule an appointment with your veterinarian if you notice that your dog’s heat cycle is irregular, if there is extended bleeding or discharge, if you think your dog might be pregnant, or if your dog’s behavior becomes abnormal. 

Why is it important to get your dog spayed? 

Spaying, also called an ovariohysterectomy, involves removing the ovaries, fallopian tubes, and uterus of female cats and dogs. These procedures eliminate an animal’s ability to reproduce and can also prevent disease and some undesirable behaviors associated with mating instincts. Benefits of spaying your female dog include: 

  • Reduced risk of certain types of cancers, disease, and infections, including pyometra 
  • Curbed unwanted behaviors associated with mating 
  • Increased life expectancy 
  • Lower long-term healthcare costs 
  • Limited unwanted pregnancy and pet overpopulation 

Discuss the benefits of having your dog spayed with your veterinarian. Not only will this protect your dog from unwanted pregnancies, the procedure will also stop the heat cycle and bleeding. If you plan to spay your dog, your veterinarian will likely recommend you wait until at least one month after her heat cycle ends.