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Sexual maturity in dogs is something puppy owners should be aware of, so to know what to expect as their male puppies mature.

While many puppy owners may never witness the most evident changes of sexual maturity due to early neuter programs, nowadays, more and more puppy owners opt to wait to neuter their pups. 

This leads to puppy owners encountering new and unexpected behaviors from their puppies that may often leave them baffled or concerned.

This guide based on information provided by veterinarian Dr. Ivana Crnec should help puppy owners get better acquainted with the timeframe of sexual maturity in male puppies and the accompanying signs. 

When are Female Dog Sexually Mature?

Female dogs become sexually mature during puberty, which in most dogs takes place anywhere between the age of 6 to 9 months. 

This great variability in time is due to the fact that dogs come in many different shapes and sizes, and therefore, they have a tendency to develop at slightly different times. 

  In general though, smaller dog breeds tend to go into heat earlier (around 4 months of age) while large and giant dog breeds become sexually mature later and go into heat at an older age (from 18 months of age to 2 years).

In order to better understand sexual maturity in female dogs, it helps to better understand a female dog's heat cycle and what happens as it takes place. 

The female dog's heat cycle is composed of 4 stages

The female dog's heat cycle is composed of 4 stages

The Stages of a Dog's Heat Cycle 

The ultimate proof a female dog becoming sexually mature is the onset of the first estrus (heat cycle). Female dogs are likely to have between one and three heat cycles each year. Each heat cycle lasts between 21 and 28 days.

While wolves tend to go in heat once a year in early spring, domestic dogs don't typically show any tendency to go in heat during specific seasons, however, some breeds may be prone to be in heat in the early fall or late winter/early spring.

The female dog's heat cycle is composed of 4 stages: proestrus, estrus diestrus and anaestrus. Each phase is characterized by different physical events. 

The Proestrus Stage of Dog's Heat Cycle

The proestrus phase usually lasts for 9 days but it can vary from 3 days to 17 days in length. During this phase the dog’s body prepares itself for a potential pregnancy. However, it should be noted that during this phase the female dog does not accept males and may even show aggression towards them. 

The proestrus is defined by 2 physical, 1 behavioral and 1 hormonal change. The physical changes include swelling of the reproductive tract and the appearance of a reddish to brown discharge (the bleeding phase). 

The behavioral change suggests the increased nervousness of the dog. The hormonal change is due to the varying levels of the estrogen that first rises and once it reaches its peak starts dropping.

Tip: Because bleeding cycles can be messy especially in larger dogs, many dog owners use some form of containment under the form of doggy diapers, crating the dog or confining to an area covered with easy-to-clean flooring.

The Estrus Stage of Dog Heat Cycle

The estrus lasts for 9 days, but it can range from 3 to 21 days. During estrus the dog's reproductive area appears swollen and soft, while the discharge decreases in both quantity and color (light reddish or pinkish to straw colored).

Since the estrogen levels are low, the progesterone levels rise. When the progesterone levels are high, the luteinizing hormone (LH) levels sharply spike causing ovulation. The female dog becomes receptive to males within 2 to 3 days after the LH peak.

The hormonal changes during the estrus phase of the cycle trigger behavioral changes. For example, female dogs may urine mark more, lick their private areas more, become flirtatious and start poking males with their noses. 

They may also investigate male urine more, push their rear ends into the males’ chests, play-bow and lift their tails up or to one side (phenomenon called flagging). 

When the female dog starts showing these signs she is referred to as being in ‘’standing heat." This is the stage during which female dogs are most fertile and likely to get pregnant. 

This is therefore the time a female dog is more likely to become pregnant. If your female dog escapes during this time,, consider there are good chances she may return pregnant. Some female dogs don't even have to escape: some have shown the ability to mate with male neighbor dogs even through a chain link fence!

Did you know? During the heat cycle, female dogs produce volatile compounds  in their urine that are normally not present in a female that is not in heat. Male dogs are very attracted to the scent. 

The Diestrus Stage of Dog Heat Cycle

The diestrus ranges in length from 50 to 80 days. This phase occurs regardless of whether the female is pregnant or not. 

The only difference is that, if the dog is pregnant, the diestrus will be a little bit shorter than it would be if she was not pregnant.

 During diestrus the dog's uterine walls thicken and certain hormonal changes occur, but there are no visible signs.

During the diestrus phase female dogs may fall into false pregnancies. This is due to the fact that the hormonal system assumes the dog will be pregnant each and every time she comes into heat.

Even when not mated, the dog will still experience the full hormonal effects of pregnancy, with all the associated physical and mental changes. 

The physical and mental changes include labor signs, milk production, rejecting food, making dens and mothering objects (usually toys).

The Anaestrus Phase of Dog Heat Cycle

As the last phase of the heat cycle, the anestrus is defined as the resting period for the reproductive tract and usually lasts around 150 days. 

During this period the female dog's body rests and then prepares itself for the next cycle. The anestrus is not marked by visible signs and the sex hormones are at their lowest.

Female dogs in heat may ask more often to be let out. 

Female dogs in heat may ask more often to be let out. 

Behaviors of Female Dog Going into Heat

The first “in season” signs a dog parent will usually notice are swelling of the vulva and blood-tinged vaginal discharge. Below are other signs suggestive of sexual maturity and associated heat cycle. 

Asking to Go Out

Dogs are driven by their instincts, and when in heat, the female dog’s instincts are telling her to mate. This mating drive is limited by you keeping her inside the house.

Therefore, females in heat, just like males, will frequently ask to go out. By ask, we mean whine, cry and scrape at the door. Depending on the circumstances, some dogs may try to escape.

Urine Marking

Urine marking is much more pronounced in males, but intact females are also prone to this unwanted behavior. In females, urine marking is generally present only during the heat cycle.

When urine marking, most female dogs will squat but some prefer to raise one of their hind legs. Before the female dog urine marks, you can notice intense sniffing of the area that will be marked.

Just like males, females like to mark low but prominent objects – fire hydrants, shoes, dog beds, or small plants.

If your dog urine marks inside the house, it is important to clean the marked areas with pet-friendly enzymatic cleaners.

Rear Showing and Flagging

When the female dog is ready to mate she will lift approach males with elevated rear end and with her tail in an almost vertical position. The tail elevation and butt-showing position are popularly termed as “flagging”.

To avoid agitating other dogs, it is best advised not to take your female dog out in public places during this phase.

If she is going in doggy day care or boarding facility, you need to accent that she is the most delicate point of the heat cycle and proceed based on the facility’s rules regarding this question.


Mounting or humping are embarrassing behaviors, but sadly common behaviors in all dogs regardless of sex and even regardless of their reproductive status. Yes, as unbelievable as it may sound, even “fixed” dogs mount!

Female dogs are willing to mount on the same specter of objects as males – pillows, dog beds, plush toys, other dogs, and people’s legs (known or strangers).

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Mounting may increase during a female dog's heat cycle. Other female dogs may also engage in mounting when a female dog is in heat. 


In addition to mounting, female dogs may be licking their genitals. Once again, the licking does not have to be sex-related. Some female dogs can lick their genitals as a stress relief, because of boredom, or due to an underlying medical issue – like, urinary tract infections.

If you are not sure where your dog’s mounting and licking urges stem from, do not hesitate to talk to a veterinarian or dog behaviorist.


In study from 2019, “Behavioral risks in female dogs with minimal lifetime exposure to gonadal hormones” researchers found that intact female dogs are more prone to excessive howling than spayed females.

This is important for dogs living in urban areas where the excess howling would be frowned upon by the neighbors.

According to the same study, intact females are less likely to return immediately when called (during off leash time) and also less likely to fetch or attempt to fetch thrown objects like sticks and balls.

Chewing Inappropriate Objects

According to the study mentioned above, intact female dogs are more likely to engage in destructive chewing of inappropriate objects.

It is not particularly clear how this behavior is linked with the dog’s spaying status. It is postulated that intact females resort to destructive chewing due to increased irritability and mood swings.

Intact females, especially when in heat can be overly attached to their owners and leaving them alone can result in separation anxiety. Destructive chewing is a known coping mechanism in dogs with anxieties.

Dislike of Other Females

Like girls tend to see other girls as competition, especially during the teenage years, female dogs see other females as rivals. This female-to-female dislike is constantly present, but mostly accented during heat.

If you have more than one intact female in the households, you will need to make special arrangements while each of them is in heat. The dislike can sometimes culminate with a fight and the consequences might require an urgent trip to the vet’s office.

It should be noted that this dislike is focused solely on females. Intact female dogs get along well with males regardless of their “fixing” status.

Mood Swings

Female dogs are prone to pronounced mood swings during heat. There are two main reasons – first, the presence of drastic hormonal changes and second, the pain some dogs feel while ovulating.

The drastic hormonal changes and ovulation pain usually make females more likely to snap and react aggressively, especially towards other females and even people. This also applies to dogs that have never shown aggression before.

On the other hand, the same reasons make female dogs more affectionate with family members and more likely to engage in cuddling sessions and attention-seeking attempts.

Differentiating a true pregnancy from a false one is not easy.

Differentiating a true pregnancy from a false one is not easy.

What Do I Do If My Dog is Unexpectedly Pregnant?

If your suspect your female dog is unexpectedly pregnant, the first thing you need to do is check whether she is truly pregnant. The tricky thing as mentioned is that dogs can go through a false pregnancy during the diestrus stage. 

A false pregnancy can produce signs of a true pregnancy and it has tricked may dog owners into believing that puppies are on the way. 

Differentiating a true pregnancy from a false one is not easy. Following is some info on what to do if you suspect your female dog is pregnant. 

Understanding False Pregnancy in Dogs

Before worrying about your dog being unexpectedly pregnant, firstly, determine whether your dog is actually pregnant. Something to be aware of is therefore, false pregnancy.

False pregnancy is a relatively common phenomenon in dogs. The condition develops in intact females and it mimics both the physical and behavioral signs of real pregnancy. In simple terms, the dog looks and acts like it is pregnant.

Usually the condition manifests in a mild form and is self-limiting – the pregnancy-like signs and symptoms last for around 14 to 21 days and then they gradually start subsiding. However, in more severe cases, medical attention and intervention are warranted.

Important is to therefore determine whether your dog is actually pregnant or not. There are a variety of ways to confirm an actual pregnancy in dogs. 

If you suspect your dog is pregnant, have her see the vet. 

If you suspect your dog is pregnant, have her see the vet. 

How To Tell if a Dog is Pregnant

The best way of finding out whether your dog is pregnant is taking her to the vet. The vet will determine pregnancy based on three possible tests.

Test Number 1 – Abdominal Palpation

The vet can palpate the dog’s abdomen and check for bulges indicating there are puppies in the uterus. The test is simple and does not require any equipment, but it has its downfalls and is not routinely recommended because it's not very accurate.. 

Test Number 2 – Relaxin Blood Test

The vet can determine whether your dog is pregnant by measuring its hormone levels. This test is based on detecting the presence of a hormone called relaxin. Relaxin is produced by the placenta and its presence is a strong indicator of pregnancy. 

The relaxin blood test is a reliable way of differentiating a real pregnancy from a false pregnancy. However, there are also some caveats. 

Namely, if performed too early while the pups are not properly developed, the test can give a false negative result. For best results, the test can be repeated after 10 to 14 days or ideally performed over 22 days post mating. Another concern is that the test does not offer insight on whether the puppies are alive.

Test Number 3 – Ultrasound Scan

The test of choice for confirming pregnancy in dogs is ultrasound. Using ultrasonography, the vet can determine the presence of puppies as early as 3 ½ weeks post mating. Additionally, the technique allows evaluating their vitality.

The ultrasound scan can give a rough estimation on how many puppies the dog expects, however it cannot determine their exact number. 

Can Dogs Get Abortions?

 Yes, abortions are an option in dogs. Although the basic abortion concept is the same as in people, the technique is different. To be more accurate when dealing with an unwanted pregnancy there are two possible options. 

Option Number 1 – Spaying Your Dog

Spaying your dog is the perfect solution if you do not plan on breeding your dog in the future. Talk to your vet about the pros and cons of performing this procedure in a pregnant dog. The procedure steps are the same as for non-pregnant dogs. However, the vet will have to be extra cautious because there will be greater bleeding risk considering that, the blood supply to the uterus increases during pregnancy.

Generally speaking, spaying your dog while pregnant is more difficult than the average routine spaying, but it is possible, and in certain situations, it is the best option.

Option Number 2 – Abortion

What can you give a dog to abort puppies? There are special drugs that can be used for abortion purposes in dogs. However, their use is strictly regulated and after being administered the dog needs to be carefully monitored by the vet.

Option Number 3- Finding Homes for the Puppies 

 Finding home for all of the puppies can be a challenging task, but it may be worthy of trying if your female dog got pregnant. 

You can contact local animal welfare organization and ask for their help. They can help you make an adoption plan, but keep in mind that it is not their responsibility to take care of your pups. 

You can always ask your friends and relatives if someone wants to adopt a puppy or post on social media. However, these activities should be done before your dog gives birth. 

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