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Heat Cycle

Dog Heat Cycle: Reproduction in Dogs Explained

The dog heat cycle is a term used to denote a dog’s reproductive phase. Dogs are “in heat” or “in estrus” when they reach sexual maturity. Think of this cycle as the animal equivalent of the menstrual cycle in human females.

Most dogs won’t have a problem with their instincts when it comes to breeding. However, several dogs will also need a helping hand from their humans in case any problems happen. Female dogs may experience reproductive infections, a difficult pregnancy, and complications while giving birth.

Behavioral changes may also occur during the reproductive periods, such as your female dog becoming too clingy to you or aggressive against male dogs. Hence, it’s important to learn more about the dog heat cycle.

In this article, we’ll look into the four stages of the dog heat cycle. We’ll also explore how to spot when your dog goes into heat, what to expect with a dog on the heat cycle for the first time, and other similar issues that baffle dog owners regarding their fur babies’ reproductive system.

The Dog Heat Cycle Stages

The dog heat cycle is medically termed as estrus
Dog in Heat - Estrus -Bark For More

This is characterized by various changes in a dog’s form, structure, and hormone levels. Different clinical signs appear throughout the stages of the estrous cycle.

Female dogs experiencing a dog heat cycle enter four different stages:

4 stages - Bark For More

1. Proestrus

Proestrus is the first stage of the dog’s heat period. Females stay in this stage for approximately 9 days, although it could be as short as 3 days or as long as 12-17 days. 

In this stage, the female dog’s body undergoes changes that prepare her to mate and breed with male dogs.

Several changes happen in a female dog’s ovaries when she enters proestrus. The follicles in her ovaries start to develop rapidly. This is accompanied by a rising level of the hormone estrogen in her body.

Higher estrogen levels prepare her ovaries and make her capable of bearing litters as the dog heat cycle continues. Estrogen is also responsible for all the outward changes you see in your dog’s body and behavior.

Once your dog enters proestrus, her vulva swells and a blood-tinged discharge starts to appear. Some dog owners don’t notice the discharge primarily because their dogs quickly clean themselves up, leaving no trace of blood-tinged discharge.

Frequent urination is also a sign of proestrus starting in females. This is accompanied by the dogs sticking their tails closer to their bodies.

Female dogs in proestrus may start attracting potential mates. However, they’re generally not receptive to male dogs yet. 

When a male dog approaches a female in proestrus, the female typically stands quietly as the male smells her.

But she will often crouch down if the male attempts to mount her. Other females even display aggressive behavior towards male dogs at this time.

Changes during Proestrus - Bark For More

2. Estrus

Estrus is the second stage in the dog heat cycle. Female dogs stay in estrus in variable time frames, but it averages around 3-4 days. Some dogs may stay in the estrus stage for longer, typically 7-13 days.

In estrus, the female dogs become receptive to advances made by male dogs. This stage is when mating takes place.

Female dogs in estrus display the following characteristics and changes:

  • Frequent urination, marking spots in your home with her urine to send pheromone messages telling males of her readiness to mate
  • A pinkish or straw-colored discharge replacing the blood-tinged discharge in proestrus
  • Less discharge than those observed in proestrus
  • Further enlargement and softening of the vulva
  • Holds her tail to the side, as if allowing males access to her vulva
  • Presents herself to intact males around her, with her hindquarters first

Estrus - Bark For More

Problems During Estrus Bark For MoreDuring estrus, males and females become interested in each other. Aggression and restlessness that females exhibited towards approaching males during proestrus are significantly gone.

Females in estrus are influenced by two main hormones:

  • Luteinizing Hormone (LH) is responsible for the release of mature eggs from the dog’s ovaries. LH levels surge just when progesterone levels are starting to rise. This surge may remain less than 24 hours up to 48 hours, depending on the dog.

Progesterone levels rise progressively as LH surges. Progesterone starts on a baseline level just before the LH surges. Once the LH rises to its highest level, progesterone begins to rise. This defines the peak fertile period of a female dog. 

At around one to two days after the LH surge (days 3-4 of the estrus stage), the female dog starts to ovulate and is capable of bearing pups when a successful mating occurs.

3. Diestrus

The third stage of the dog heat cycle is called diestrus. This often comes right after the estrus stage ends, at around the 14th day of the cycle. Again, this time frame may vary between different dogs, but it is fairly consistent regardless of dog breed or size.

Diestrus marks the final or luteal stage of the dog heat cycle. This is characterized by the dog’s reproductive system coming to rest if she isn’t impregnated during estrus. Her body will exhibit changes once again:

  • Her vulva returns to its normal size
  • Discharges become reddish until it tapers off
  • Females return to a non-receptive state towards approaching males

Non-pregnant dogs display pseudopregnancy during diestrus. This is because progesterone (the pregnancy hormone) may remain elevated during diestrus, even when a pregnancy did not occur after mating. Pseudopregnancy is a common feature and almost all non-pregnant females experience this during diestrus.

Once the progesterone starts wearing off, another hormone called prolactin increases. Prolactin is secreted by the pituitaries and is largely responsible for signs of pseudopregnancy in dogs. The hormone influences the female dogs to display a maternal behavior needed for delivery and litter care after pregnancy. 

Pseudopregnancy can be exhibited by non-pregnant dogs through the following behaviors:

  • Nesting
  • Showing aggressive behaviors
  • Mothering of toys
  • Development of mammary glands and lactating

Pseudopregnancy - Bark For More

Now, if a dog becomes pregnant during estrus, she enters the diestrus phase to complete her pregnancy. Dogs generally remain pregnant for 58-68 days. Specifically, the gestation period in dogs is approximately:

  • 58-72 days after the first time a female dog is allowed to breed
  • 56-58 days after the first diestrus day
  • 64-66 days after progesterone levels initially rises 

Gestation Period in Dogs - Bark For More

Diestrus is completed when all signs of vulvar swelling and discharge disappear. This typically occurs 60-90 days in non-pregnant dogs. Diestrus for pregnant dogs ends once she gives birth to her puppies.

4. Anestrus

Anestrus is the last stage of the dog heat cycle. This is characterized by the time between the last diestrus and the next proestrus. Female dogs typically stay in anestrus for 3-5 months, although larger breeds may go through a longer anestrus phase.

Characteristic changes in anestrus include:

  • Uterine healing, especially after a pregnancy
  • The vulva has completely returned to its normal size with no swelling
  • Vaginal discharges are absent
  • Female dogs go back to being entirely non-receptive to males

Anestrus - Bark For More

Hormone levels in female dogs tend to stabilize during anestrus. The dog’s body is also preparing the uterus for the next proestrus stage, signaling an end of one entire dog heat cycle.

Dog Heat Cycle for The First Time

Unspayed female dogs usually enter their first dog heat cycle when they’re around 6-24 months old. 

Smaller-breed dogs such as Yorkshire Terriers and Chihuahuas tend to start their estrous cycles earlier than large-breed dogs like St. Bernards and Great Danes. Small-breeds may experience their first heat as early as four months old. Big breeds may get their first heat as late as two years old.

Breeds - Bark for More

A dog entering the estrous cycle for the first time may experience irregularities before her cycle stabilizes to a noticeable rhythm. At times, it takes up to 18 months before a dog’s heat cycle becomes regular.

How Often Do Dogs Enter the Dog Heat Cycle?

Generally, unspayed female dogs go into heat twice a year. This typically happens every six months, for a total of two cycles per year. 

Younger dogs may experience the estrous cycle in varying lengths for the first few cycles of their lives. This is normal as their cycles haven’t matured and stabilized yet.

Small dog breeds may experience the heat cycle more frequently. The estrous cycle often repeats itself up to 3-4 times a year in such dogs.

On the other hand, large dogs may rarely go into heat as frequently as small breeds do. Some giant dog breeds experience the heat cycle only once a year. Furthermore, giant dog breeds may even take 18 months to start another heat cycle. That’s well over a year of not being reproductive and fertile.

Is my dog in heat? - Bark For More

Do Male Dogs Go into Heat?

No, males do not have a specific dog heat cycle nor do they enter the estrous cycles experienced by females. 

A male dog starts to become sexually mature as early as 6-9 months of age. Full sexual maturity is completed by 12-15 months of age. During this time, male dogs are at the peak of their fertility.

Males remain fertile their entire lives, beginning from their adolescent stage. Hence, they can impregnate female dogs in the heat all year round. Characteristics of fertile males may include:

  • Frequently roaming around
  • Urinating to mark territories and send signals to females
  • Sniffing around tracking the scent of a female in heat
  • Increased aggressiveness
  • Mounting on female dogs
  • Decreased appetite

Male Dogs - Bark For MORE

A lot of these characteristics lean toward a negative behavior and may cause chaos for dog owners. Hence, pet parents of male dogs who aren’t neutered must focus on keeping their dog away from in-heat females if they don’t have the intention to breed. 

Male dogs will benefit the most from early puppy training (1) to prevent behavioral issues when they become sexually mature.

Is the Dog Heat Cycle a Lifetime Thing?

Yes. Once a dog starts getting heat cycles, this will continue through the rest of her life. If you compare it to humans, it’s like saying that dogs will never experience a menopause phase.

What happens instead is that the time in between dog heat cycles gets spaced longer and longer as the dog ages. But through it all, the dog remains fertile during the estrus stage as long as she lives.

The dog cycle can only be stopped by spaying a female dog. If a dog is spayed, her dog heat cycle halts along with behaviors that indicate breeding instincts.

Spaying: The Best Way to Prevent the Dog Heat Cycle

You may elect to have your female dog spayed if you’re not raising her to breed. It’s the best way to prevent the occurrence of a dog heat cycle.

Spaying is a medical procedure that removes a female animal’s reproductive organs. It is a routine surgery often performed by veterinarians on female puppies anytime after 8 weeks of age. 

Spaying is ideally done before a female pup experiences her first dog heat cycle. However, some veterinarians wait until the first heat cycle is done to ensure that the dog has reached sexual maturity before spaying her. 

Early spaying may also affect a dog’s orthopedic growth if done too early, so some vets wait for the growth plates to close before spaying the dog. 

Until then, behavior analysis (2) and positive behavioral training plays a major role in keeping the dog safe during a dog heat cycle.

Spaying has several benefits for a female dog, including:

  • A reduction in the stress, discomfort, and behavioral changes experienced by female dogs during the heat cycle
  • Reduces mammary cancer risk
  • Lowers down the risk of contracting uterine cancer
  • Significantly reduces risks of contracting contagious illnesses spread through a bodily fluid exchange (such as through mating)

Spaying in Dogs - Bark For More

Apart from eliminating the dog heat cycle, spaying is also the answer to overpopulation in dogs. Statistics show that in the United States, 15 dogs are being born for every human baby that comes into life (3)

Several puppies have a hard time finding suitable homes because of these birth rates, and the dilemma blooms into a full-blown dog overpopulation. That’s why spaying female dogs are highly recommended by veterinarians.

Spaying should be discussed in-depth with your veterinarian. It’s not a light decision to make, and your vet’s inputs may shed light on your final judgment and decision.

Caring for a Female Dog in Heat

If your female dog is intact and she experiences a dog heat cycle, you can help ease her stress and discomfort through these care tips:

  • Strike a balance between rest and exercise. Some dogs may feel tired all day long when in heat. Others may be too restless and need calming. Let your dog rest if she’s too tired and allows her gentle exercise when she’s up to it. Otherwise, calm her when she’s in a restless mood.
  • Give your female dog extra attention when she’s in heat. Make yourself available for some extra brushing, playing, talking, and going out for walks. Interacting with your dog makes her feel calmer during this stressful heat period.
  • Be extra cautious when walking your dog. Use a leash when taking her out, even if she is well-behaved on obedience training. Instincts can quickly overcome any training when she is in the middle of a dog’s heat cycle.
  • Don’t keep your female dog in heat outside alone. Supervise her and put her on a leash, if possible. You’ll never know when a male dog suddenly jumps in.
  • If you must leave your dog inside the house, give her chews or toys. Chewing is a great anti-stress coping action for dogs. It’ll keep her busy and put her restless thoughts away while you’re outside the house.
  • Avoid dog shows, group training, or any events where dogs may congregate. Male dogs will get distracted when a female dog in heat appears in their midst, what with the scents and pheromones she emits.

Finally, only have your female dogs breed after completing two normal heat cycles. Breeding her earlier may cause health problems for both her and the resulting litter.

Dog Heat Care Tips - Bark For More

Final Thoughts

The dog heat cycle is the hallmark of a female dog’s reproductive capabilities. Experiencing a cycle means that your female dog is ready for mating and breeding. 

The four stages of the dog heat cycle – proestrus, estrus, diestrus, and anestrus – all work together to allow your female dog a chance to become a mother to puppy litters.

The heat cycle’s length and rhythm vary depending on the dog’s breed and individual health status. But once a pattern has been established, the dog heat cycle becomes fairly regular and lasts through the female dog’s entire lifetime. Do check in with your dog’s vet for any irregularities you may observe.

Spaying is the best way to prevent a dog’s heat cycle from occurring. It’s recommended to have your female dog spayed if she isn’t raised to become a breeder. 

If spaying isn’t the way to go, there are many ways to care for your dog in heat. You can calm her down and keep her safe from prying males with a little bit of extra effort on your part.


(1) Dunbar, C. (2018). Puppy training 101: The essential guide to raising a puppy with love. 

(2) O’Heare, J. (2017). The science and technology of dog training (2nd ed.). BehaveTech Publishing.

(3) Dunbar, C. (2018). Dogs: 101 amazing dog fun facts and trivia for kids.


Related Articles:

How to Spay and Neuter a Dog – A Step-By-Step Guide

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