When Your Boxer Goes Into Heat: What To Expect

There is a lot to understand about managing an unspayed female Boxer’s heat cycles.

As the owner of a sexually intact female, you will want to know how to read the signs she’s going into heat, how to keep your girl comfortable and how to recognize if something has gone wrong with her reproductive system e.g. the uterine condition known as pyometra.

When your female Boxer is in season, she will attract at times very forceful attention from intact male dogs, her scent detectable from literally miles away.

This comprehensive article attempts to leave no heat-related question unanswered.

I am not a vet. This post is for informational and general educational purposes. I encourage readers to view my full disclaimer here. Boxer Dog Diaries is reader supported. I may receive a small commission, at no extra cost to you, if you buy via links I share.

When Do Boxers Go Into Heat For The First Time?

The timing of a Boxer’s first heat varies from dog to dog.

A common timeframe for the initial season in Boxers is between six months to one year.

However, it can be as early as four months or as late as 15 months.

If your Boxer has reached two years old and you don’t think she’s gone into heat yet, there are a couple of possibilities:

  1. She may have had a “silent heat” that you didn’t notice (Especially if there were no male dogs around to pick up on it)
  2. She may just be a little late
  3. You may like to have her examined to make sure everything’s okay

Keep in mind that Boxers in general are a slow maturing breed, not considered fully adult until two years and even a bit beyond.

Note that recent research has discredited the old belief that spaying a dog prior to her first heat cycle prevents mammary cancer.

In fact, we now know it is far healthier for a female Boxer to keep her ovaries and uterus — just as it’s healthier for a male Boxer to retain his testes.

One of the issues is that when you remove the hormone-producing sex organs, it overtaxes the remaining endocrine tissue which can trigger a range of disorders.

More on this later.

How Often Does A Female Boxer Dog Have A Season?

You can expect your Boxer to go into heat about twice a year or so, maybe a little less often.

This is only a rough guide.

Each dog is different.

After two or three heat cycles you should have a good idea of your girl’s individual pattern.

Then again, one study suggests the variation in cycles can actually be greater within the one dog over her lifetime than between different dogs.

Heat cycles can be affected by:

  • Medication like corticosteroids (Here is what prednisone did to my young male Boxer.)
  • Stress
  • Health status
  • Nutrition
  • The cycles of other females in the same household
  • Age (There will probably be longer between heats as your Boxer gets older.)

There is conflicting information as to whether small or large breeds cycle more frequently.

Some sources advise that smaller breeds come into heat every four months, medium breeds every eight months and large ones every year or more.

But the University of Louisiana veterinary reproductive specialist Dr Bruce Eilts says that, contrary to what many people believe, larger dogs tend to come into heat more often than smaller breeds.

How Long Does A Boxer’s Heat Cycle Last?

The whole heat cycle lasts about three weeks to a month, but your Boxer does not bleed, and is not fertile, for that entire time.

A general rule of thumb is that a dog takes about a week to come into heat, spends another week actually in heat and then takes another week to transition out of heat.

Particularly when a dog is young, cycles can be irregular, both in terms of how long each heat lasts and how long elapses between heats.

This is why it’s great advice to always “watch the dog, not the calendar”.

The bleeding usually only lasts a week or so.

Note that the window of fertility does not coincide with the blood.

Rather, the fertile period begins just as the bleeding eases up, and lasts for about another week.

For the rest of the year, your Boxer is between cycles.

Signs Your Boxer May Be Going Into Heat

The first sign that a Boxer is going into heat is usually a swollen vulva, caused by an uptick in estrogen.

Of course, the definitive indication is a bloody discharge, which breeders refer to as “showing color”.

In practice, given some dogs have heats without clear outward signs (silent heats) the most reliable indicator your female is approaching heat is often a social one: how male dogs behave around her.

The most common signs a female Boxer is in heat include:

  • Swollen, spongey-looking vulva which may turn a dark red color (First sign)
  • Bloody discharge (Surest sign, initially bright red then fading to pinkish or tan colored)
  • Enlarged nipples (Usually hard to notice)
  • Licking herself
  • Scent marking
  • Increased male interest in her, followed by increased interest on her part in males (Unmissable signs)
  • Tail flagging (Holding the tail up and to the side, an indication she is seeking to mate)
  • Mood changes — oversensitive, and either cuddlier or crankier with other dogs and people

The bloody discharge associated with a heat is not to be confused with anal gland secretions which have a pungent, unmistakable odor.

What Happens During A Boxer’s Heat Cycle

Your Boxer’s heat cycle is a weeks-long process that begins before, and continues after, the observable bleeding.

The details can get a little confusing, but a female dog is always in one of four hormonal stages:

  • Proestrus
  • Estrus
  • Diestrus
  • Anestrus

The heat itself is made up of the first two hormonal stages: proestrus and estrus.

Your Boxer will bleed during proestrus but is not fertile until estrus.


This is the “getting ready” period as your Boxer’s body prepares for possible mating.

It goes for about nine days on average but can last anywhere from three to 17 days.

During this phase, estrogen levels rise, causing the eggs inside the ovaries to begin maturing.

The vaginal walls — as thin as an eyelid for the rest of the year — thicken in preparation for the friction or “trauma” involved in sexual intercourse.

It is this increased blood supply to the area that causes the bleeding during proestrus (which is different to what happens in the human menstrual cycle, as we’ll explain later in the article).

At the end of proestrus, testosterone levels are actually relatively high too.

The surge of this male hormone may prompt some masculine behavior in your girl, such as mounting other dogs.

Throughout proestrus, males will be attracted to your female but she won’t allow mating, perhaps even responding aggressively when they try.

Her vaginal walls are not yet ready.

Nor are the eggs.


Estrus is when the eggs are released from the ovaries.

The estrogen that peaked during proestrus abruptly declines.

Now, levels of a different hormone, called progesterone, rise.

The bleeding that defined proestrus stops, lightens to a pink or straw color or looks more mucousy.

This is when your Boxer is fertile and ready to mate.

At this point, not only will males be interested in your girl, but she will be attracted to the males.

This is when she may “flag” her tail, lifting it to the side as though to offer access, and moving the tail to spread her scent around.

Only now will she be receptive and submissive to males.

A female usually ovulates on day three or four of estrus, with the eggs staying alive for five to six days.

In other words, your female Boxer becomes fertile three or four days after the bloody discharge begins to look clearer, or stops.

This can be a trap for owners who can mistakenly think that once the bleeding stops, the cycle is over.

In reality, this is right when the female dog is most receptive and fertile and it’s the best time to get pregnant.

Like proestrus, estrus lasts about nine days on average, but can be as short as three days or as long as 21.


The heat is now over and your Boxer may have entered pregnancy.

Diestrus lasts 58 to 63 days (nine weeks) in a pregnant female or 60 to 90 days in a non-pregnant female.

With the hormone progesterone now dominating, the female will revert to refusing male advances.

In fact, the change in your female’s behavior toward male dogs is what will usually tell you that her heat has finished.


This is the resting phase between heats, or the recovery period after pregnancy and before the next heat.

As during diestrus, your Boxer cannot get pregnant during this phase.

Diestrus and Anestrus combine to make up most of the year.

Can You Breed A Boxer On Her First Heat?

Can a 13-year-old human get pregnant and have a baby?


But is it a great idea?

There are several reasons you should not breed a Boxer on her first heat, such as:

  • Immature eggs
  • Her own immaturity as a dog
  • It’s too soon to test for heritable diseases
  • Increased risk of difficult labor

Immature Eggs

Your Boxer probably won’t be very fertile in her first few seasons because her eggs aren’t yet fully mature.

Her Own Immaturity As A Dog

At the point of her first heat, your Boxer is still developing.

Though the first heat cycle signals sexual maturity, your Boxer is still a puppy mentally and in an overall physical sense.

To cope best with pregnancy and motherhood, and to be the best mother, she should complete her own development first.

Health Testing

Boxers aren’t old enough at their first heat to show their own true health status.

They are also too young to get reliable results from the various tests necessary to determine they won’t pass on any of the genetically-based conditions the breed can be prone to.

Labor Trouble

Dogs mated on their first heat tend to have more problems with labor than dogs bred later.

Puppies — and the mothers themselves — can die when labor goes wrong.

If you have found a Boxer puppy that comes from a female bred on her first heat, it may well be cause to question the quality of the breeder.

Here are 24 must-know questions to ask your Boxer breeder.

Can A Female Boxer Get Pregnant When She’s Not In Heat?

No. (As explained earlier.)

However, it’s important to know that dogs can have silent heats or, as discussed, you may misjudge when her heat ends and think it’s done when she’s actually at peak fertility.

The important thing to remember is that the bleeding does not coincide with the fertile period.

When the bleeding lightens from bright red to a pinkish color, or stops, your Boxer is entering her fertile window.

Usually this is 11 to 13 days after she first “showed color” i.e. when the bleeding started.

How Long After A Boxer’s Heat Can You Tell If She’s Pregnant?

28 days post mating, an ultrasound can detect pregnancy.

If you are considering breeding your Boxer, here are some questions to ask yourself.

How Much Blood Is There During A Boxer’s Heat Cycle?

This varies: some bleed enough to make a mess in the house, others bleed so little you barely notice.

All you see may be a stray spot of blood in the sidewalk.

Boxers in heat will usually lick themselves clean and may even do their best to clean up any drops of blood.

How Is A Dog’s Heat Different To A Woman’s Menstrual Cycle?

A dog’s heat is not the equivalent of a human female’s menstrual cycle.

In women, menstruation is the shedding of the uterine lining that had been prepared to nourish the possible implantation of an embryo.

In a dog’s heat cycle, the blood comes from a totally different source.

The blood is a side effect of the increased blood supply to the canine vagina which happens in order to thicken the vaginal lining in preparation for mating (to withstand the physical “trauma” of mating).

In between cycles (i.e. for most of the year) the female dog’s vaginal lining is no thicker than an eyelid.

This is very different to a human’s vaginal lining and is because dog don’t engage in any sexual activity between cycle.

As a result, there’s no need for the vaginal lining to be tough all the time.

So, the cessation or lightening of the bloody discharge in the female dog signals the vaginal lining has finished thickening and the dog is now entering her fertile period.

There are similarities between a human menstrual period and a canine heat in that both females may experience changes in appetite, energy levels, mood and sometimes diarrhea.

These effects are due to the influence of hormones in both cases.

Is A Boxer Dog In Pain During Her Heat Cycle?

As it’s not the same process as a human menstrual period, a dog’s heat probably doesn’t involve pain or cramping.

The vaginal lining is being built up, rather than being shed and expelled.

However, your Boxer may still feel out of sorts at times, as hormones course through her body.

How To Prepare For Your Boxer’s First Heat

One of the most important ways you can prepare for your Boxer’s first heat is by getting familiar with what her body looks like when it’s not in heat.

That way, you will be in a better position to spot the swelling in the vulva that indicates a heat is on its way.

Some dogs will have not a silent heat but a very quiet one.

If the swelling is the only sign and you miss it, you won’t know what’s going on.

Pay attention, too, to how male dogs behave around your female, and even how they behave around her urine in the yard.

As far as the potential mess is concerned, you may get lucky and hardly notice a thing.

Or you may want to stock yourself with some “bitch’s britches”, pants specially designed for dogs in heat, in order to protect your carpet, furniture, bedding and couches.

Alternatively you can improvise and use:

  • Boy’s underwear, worn backwards to put the tail through the hole
  • Human diapers that can tighten with sticky tabs
  • Pull ups (though some find they fall down when the tail wags)

If your girl has a very light heat, it may be as simple as putting a towel down where she normally lies.

What you don’t want to do is kick her out of her normal spots during her heat — she will already be feeling delicate and this won’t help.

Supervise your Boxer carefully if you’re using any diapers etc to make sure your girl does not attempt to remove and eat the soiled material.

This could pose a major risk of intestinal obstruction requiring surgery.

How To Manage Your Boxer’s Heat Cycles

The most pressing issue during your Boxer’s heat is to protect her from intact male dogs or they WILL mate and you’ll have an unplanned pregnancy on your hands.

It’s not just males that go AWOL in search of a mate.

Once your girl enters the fertile phase of her heat, she may become an escape artist or roam despite having never displayed any such tendencies in the past.

More on managing the sex drive and male attention in the next section.

Other things to be aware of include:

  • Your girl may become either more needy or more aloof during her heat. Either way respect her choice and respond accordingly. She may display restlessness or seem anxious. This is normal and will pass. Soothe her in whatever ways work. She may appreciate a raw meaty bone to take her mind of it. Relaxation music specially designed for dogs can help.
  • She might lose her appetite. Respect that too. (Never force a self-fasting dog to eat. She can go for many weeks without eating and dogs do in the wild all the time. This is not a problem — quite the opposite. Fasting actually confers many health benefits that are increasingly documented in the scientific literature.)
  • When it comes to exercise during her heat, let your Boxer set the activity levels. A walk may be just the ticket or her energy may be low and she’d prefer a nap.
  • You may observe diarrhea due to the hormones. This will pass and fasting will help. Just make sure fresh, pure water is always available. (Here is why your Boxer should not drink tap water.)

Male Dogs And Your Boxer’s Heat

During your female Boxer’s heat, males will come out of the woodwork.

Male dogs can detect a female in heat from as far away as three miles (4.8km).

They are smelling her pheromones.

Even the scent of her urine can have this effect.

Remember, your girl will be attractive to males throughout her whole heat (proestrus and estrus) but she will only be receptive to males during the estrus phase, when she is fertile and ready to mate.

If you count the very first day of bloody discharge as day one, day nine is the day to begin assiduously keeping unneutered males away — but it’s safest to separate them as soon as you notice a swollen vulva, keeping them apart for a few weeks or for as long as a month, to be sure.

During the fertile period of usually about a week, a normally well behaved female may suddenly scale the fence and run away in search of a mate, so prevent this ahead of time by making sure she doesn’t have the opportunity.

Before she’s receptive, there can be a different kind of problem: she may exhibit aggression if males try to approach, in an effort to fend off unwanted attention.

Aggression between males can also be an issue as they compete for access to her.

This can take the form of fights between male dogs either within the household or out and about.

Unneutered male dogs living in the same home as a female dog in heat can be quite dramatically affected.

Your male dog might:

  • Become frantic, working himself into a highly agitated state
  • Stop eating as he focuses singlemindedly on the female
  • Display aggression towards other males, even when the female is not around, like when he’s being walked on his own

Don’t underestimate this force of nature.

Males will do almost anything to get access to a female in heat.

There are accounts of dogs ripping doors off hinges.

It can be a good idea to implement a “two door” policy of having at least two secure doors between all males and the female in heat.

A crate can count as one door.

Diapers are not chastity belts and won’t stop accidental matings.

Dogs can reportedly mate through fences and crates.

Take more precautions than you think necessary

This means 100 per cent supervision when outside the house or in the same space as a male and being on leash at all times when in public.

You may want to walk your female at different times and in different places while she’s in heat, to avoid other dogs.

You will certainly need to stay away from other off-leash dogs during this time.

Can Intact Female And Male Dogs Live In The Same Household Without Unwanted Litters?

Yes, but it takes vigilance and commitment on the part of the owner and all members of the household need to be on board.

While the effort required to keep males and females apart during the heat might seem onerous, remember this only happens once or twice a year.

In between cycles your female is not fertile and cannot get pregnant.

More to the point, dogs of different genders will show zero sexual interest in each other between heats.

In other words, while you need to pay close attention all the time so you notice when a heat is on the way, you don’t need to keep the dogs separated or constantly supervised all year round.

What If Your Boxer Has An Accidental Mating During Her Heat?

You may or may not have a problem, depending on whether your girl was fertile at the time.

If she instigated the contact or welcomed the male attention, chances are she was in estrus and fertile.

Even then, just as with humans, not every instance of sexual intercourse will result in conception.

There are drugs that can terminate a pregnancy in dogs, as in humans, but you really don’t want to let it come to this.

It does only take an unguarded minute or two, a door left accidentally ajar or a momentarily distracted owner.

So, supervision must be complete for the duration of the heat.

That said, most owners are perfectly capable of preventing an unwanted mating.

Is It Better To Spay A Boxer Than Let Her Have Heats?

Spaying and neutering is highly normalized in the United States, to the the point that in some circles keeping a dog intact can be regarded as “irresponsible” dog ownership.

To the contrary, the overwhelming weight of scientific evidence is that it is much better for the health of the dog, male or female, to remain entire.

The hormones produced by the sex organs have a protective effect on overall health.

Many diseases that already occur with increased frequency in Boxers are made even more likely by spaying or neutering.

Here is more information about what neutering or spaying does to your Boxer’s health.

Suffice to say that keeping your dog intact is a very sound decision — but it does come with the added responsibility of preventing unwanted matings, as well as some inconvenience and potential mess once or twice a year.

Heats, Having One Litter And Pyometra In Boxers

It’s sometimes said that having one litter lowers the chances that a female dog will develop pyometra.

Pyometra is a condition in which the uterus fills with pus.

It can be fatal if untreated, either via bacteria and toxins infecting the bloodstream or the uterus rupturing.

According to VCA Animal Hospital, pyometra usually occurs two to eight weeks after an estrus.

If your female appears unwell at about this time, particularly if she gets very sick very fast, consider pyometra as a possibility.

The signs of pyometra include:

  • Slight vaginal discharge (Only in “open” cervix pyometra, in “closed” pyometra there will be no drainage.)
  • Distended abdomen (Especially in “closed” pyometra as the fluid builds up in the uterus.)
  • Painful abdomen
  • Increased water consumption
  • Increased urination
  • Lack of appetite
  • Listlessness
  • Vomiting
  • Diarrhea

After many years of estrus cycles without pregnancy, the uterine wall is said to undergo changes that make pyometra more likely in older females.

Pyometra is perhaps the only reason to spay a female as a dog cannot develop a diseased uterus if the organ was removed when it was healthy.

Having said that, if pyometra occurs, the usual treatment is an ovariohysterectomy (spaying) — although this will now be an emergency surgical procedure and a more complicated operation than a routine spay.

There is a non-surgical treatment for pyometra using hormones called prostaglandins but this approach has a lower success rate.

Pyometra is said to affect 23 per cent of intact females.

It kills about one per cent.

It’s worth keeping in mind that the veterinary understanding of pyometra is drawn from a population of largely kibble-fed, over-vacccinated, chemically wormed and flea and tick treated dogs.

Like many diseases common in the pet dog population but unseen or exceedingly rare in wild dogs, it’s possible the factors involved in pyometra’s genesis may be mitigated by natural rearing, avoidance of toxic exposures and proper feeding of a biologically-appropriate raw diet.

Here is our 7 Day FREE eCourse on how to raw feed your Boxer.

Recessed Vulva And Heats

If your young Boxer has a recessed vulva, it may self-correct after a couple of heat cycles.

Heats And False Pregnancy In Boxers

“False” or “phantom” pregnancy, technically known as pseudocyesis, can sometimes happen after a heat cycle.

This involves a dog going through the behavioral and even physical (including hormonal) changes associated with pregnancy, despite not being pregnant.

All female dogs go through some hormonal changes after each heat cycle but most show no observable signs.

Signs of a false pregnancy include:

  • Sagging belly due to relaxed pelvic ligaments
  • Nest building behavior
  • Adopting a toy as their “puppy”
  • Milk production in some dogs

Dogs that do this repeatedly are thought to be at higher risk of pyometra.

Heat Cycle Abnormalities

As well as silent heats, dogs can sometimes experience other abnormalities including:

  • Absent heat / failure to cycle
  • Split heat (Can sometimes happen in young females but normalize thereafter. This is when a dog gets the vulvar swelling and bleeding but goes out of heat before progressing to the fertile stage, the second part of the heat happening after a delay of two weeks to three months.)
  • Prolonged heat
  • Prolonged time between heats (Defined as more than 16 months.)
  • Short time between heats
  • Premature ovarian failure (Losing fertility at a young age.)

Medical issues may be at play such as:

  • Hypothyroidism — can cause absence of heat (Get a thyroid blood test.)
  • Cushing’s disease
  • Ovarian hypoplasia (Immature ovaries that produce insufficient estrogen)
  • Immune-mediated inflammation of the ovaries (Can cause absent heat)
  • Ovarian tumors (Also can cause absent heat)

If a dog’s cycle is irregular, it can help to have her spend time with other female dogs that are cycling normally.

Sometimes this brings her into a regular rhythm.

If abnormalities persist, vets can do various tests including:

  • Vaginal cytology
  • White blood cell count
  • Progesterone levels
  • Ultrasound (Can detect ovarian tumors or an immature uterus)

Treatment may involve the use of hormones, often gonadotropins.

If your Boxer is having problems, try to find a vet experienced with reproductive health as well as with the Boxer breed.

When Will A Female Boxer Stop Having Heats?

It’s common for female dogs to begin to lose ovarian function once they reach six years of age.

The gap between heats may lengthen once a dog reaches eight years old, at which point she’s considered a senior Boxer and should be treated accordingly.

Most dogs stop having heat cycles altogether beyond ten years of age.


Heats are part and parcel of keeping an intact female Boxer but can be effectively managed with a little knowledge, commitment and planning.

Deciding not to spay your Boxer has many benefits for her overall health, but comes with responsibilities and some hassle once or twice a year.

Here’s a fun nerdy fact to finish: a reproductive vet is called …. a theriogenologist.

Throw that into your next conversation with a know-it-all dog owner!


Why I’ve Had a Change of Heart About Neutering Pets, Dr Karen Becker, Mercola Healthy Pets, September 30, 2013

Bouchard, G.F., Gross, S., Ganjam, V.K., Youngquist, R.S., and Concannon, P.W. Oestrus induction in the bitch with the synthetic estrogen DES. J.Reprod.Fertil. Suppl.47:515-516, 1993.

Eilts, Bruce, DVM, The Normal Canine Estrous Cycle, Louisiana State University School of Veterinary Medicine

Farricelli, Adrienne, How To Help a Dog in Heat, PetHelpful, 2020

Mobley, Everett, DVM, Dog “Heat” Cycle Basics, Kennett Veterinary Clinic

Risvanli, Ali et al, Abnormalities in the Sexual Cycle of Bitches, Peer-reviewed chapter, 2016

Signs and Stages of the Dog Heat Cycle, Breeding Business, 2015

Ward, Ernest, Pyometra in Dogs, VCA Hospitals

Dog Heat Cycle — Frequently Asked Questions, Breeding Business, 2017

Abnormal Heat In Dogs: Silent, Absent, Prolonged, Split etc, Breeding Business, 2016