What Happens During a Dog’s Heat Cycle
A dog’s heat cycle consists of four distinct stages: proestrus, estrus, diestrus, and anestrus. During proestrus, the first stage, estrogen levels increase and ovaries start to enlarge. A bloody vaginal discharge will be present, but the female will not allow mating. This stage lasts roughly 9 days on average. Next comes estrus, also known as “heat.” This is the period where a female dog is receptive to breeding and will allow mating. There is vaginal bleeding, changes in behavior, and the vulva becomes swollen. Estrus lasts around 9 days as well. Diestrus, the third stage, is when progesterone levels rise to prevent conception and the female is no longer receptive. If conception does occur, progesterone aids in maintaining pregnancy. Diestrus lasts between 2-3 months. Finally, anestrus is the resting stage with no sexual activity. It lasts 4 to 5 months until the cycle starts over with proestrus. The entire heat cycle from one proestrus to the next averages 6-8 months in length.
How Long Does a Dog’s Heat Cycle Last?
The average length of the complete heat cycle for a dog is about 6 months. However, heat cycles can vary from breed to breed and even from dog to dog. Here’s an overview of the typical timeline:
On average, puberty or the first heat cycle begins around 6-12 months of age. The entire heat cycle lasts about 18-24 days. A dog’s heat consists of four distinct stages:
- Proestrus – vaginal discharge, males attracted. Lasts ~9 days.
- Estrus – swelling; ovulation occurs. Lasts ~9 days.
- Diestrus – discharge subsides. Lasts ~60-90 days.
- Anestrus – sexually inactive. Lasts ~3-4 months.
After this cycle is complete, the stages will repeat again about every 6 months. The entire cycle from start to finish averages 4-6 months. However, this can range from as short as 3 months to as long as 12-18 months depending on the individual dog.
Length of Each Stage
The heat cycle for a female dog consists of four distinct stages, each with different durations:
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Proestrus – This first stage lasts approximately 7-10 days. The vulva begins to swell and bleed. Male dogs will be attracted, but the female will not be receptive to breeding.
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Estrus – The estrus phase lasts approximately 5-10 days. The blood discharge lightens and then stops. The female is now receptive to mating with males.
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Diestrus – Diestrus lasts 60-90 days if the female dog is pregnant, or 60-100 days if not pregnant. Hormone levels return to normal and the vulva returns to its normal size.
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Anestrus – Anestrus is the resting phase that lasts 4-5 months. The female will have no sexual interest in males during this stage as hormone levels remain low.
The specific duration of each stage can vary between breeds and from dog to dog. On average though, an entire heat cycle will last 4-6 months from start to finish.
Signs of Heat
You’ll notice both physical and behavioral changes in your dog when she enters her heat cycle. The most obvious sign is vaginal bleeding or discharge. This typically starts off light red or bloody in color, and then progresses to a pink or straw-colored discharge near the end of the cycle. Some dogs are quite messy during this time, while others keep themselves very clean.
In addition to vaginal discharge, your dog’s vulva will become swollen and enlarged. Her mammary glands may also enlarge. It is also common for the dog’s urine to contain blood when she is in heat. Before ovulation, she may frequently lick or pay attention to her genital area.
You can expect your dog to be easily distracted, restless, and vocal when in heat. Her appetite may fluctuate and she may pace or seem anxious. Interactions with male dogs result in flirtatious behavior like play bows, tail wagging, and posturing. After ovulation, the female is receptive to mating and will stand to be mounted. Once the heat cycle ends, she will no longer allow this behavior.
When to Expect First Heat
Most dogs experience their first heat cycle between 6 and 24 months old. Smaller breeds tend to go into heat earlier, while larger breeds go into heat later. Here are the general age ranges:
- Small breeds: 6-12 months old
- Medium breeds: 9-15 months old
- Large/giant breeds: 12-24 months old
The onset of puberty depends on breed, size, nutrition, and overall health. Reaching puberty requires that the dog has adequate body fat, so malnourished or underweight dogs may start cycling later. Veterinarians can run tests to check hormone levels if a dog does not go into heat by around 18-24 months old depending on the breed.
Heat Cycle Frequency
On average, a female dog will have her first heat cycle between 6-24 months old. However, this can vary substantially between breeds.
Small dog breeds tend to go into heat more frequently, starting their first cycle as early as 4 months old. Large and giant breeds can take up to 2 years before having their first heat.
After the first heat cycle, most dogs will go into heat twice per year, or about every 6 months. Although cycles can range from 4 months to 12 months apart.
Each heat cycle lasts 2-4 weeks on average. This makes the total time a dog is in heat add up to 4-8 weeks per year.
The frequency of heat cycles tends to decline with age. Many female dogs go into heat every 6 months until around age 2-5 years when it slows down to yearly cycles. Dogs will stop going into heat completely after 8-14 years of age.
Factors Affecting Cycle Length
The length of a dog’s heat cycle can vary substantially depending on several factors:
Breed – Some breeds, like Chihuahuas, tend to have more frequent and shorter cycles, while breeds like Siberian Huskies experience them less often. Herding breeds like German Shepherds typically have cycles lasting 3-4 weeks.
Size – Larger dogs tend to start cycling later and have longer cycles. Small dogs reach sexual maturity faster and can start as early as 4 months old.
Age – A dog’s first heat usually occurs between 6-24 months old. Older dogs often have irregular cycles.
Reproductive Status – Intact dogs have normal cycles until senior years. Spaying stops the cycle unless done mid-cycle.
Health – Thyroid disorders, infections, obesity, and other health issues can disrupt normal cycles.
While averages exist for breeds, each dog is an individual. It’s ideal to understand your own dog’s unique cycle pattern over time.
Dealing with a Dog in Heat
When your dog goes into heat, it can be challenging to manage them and keep them comfortable. Here are some tips for owners on handling a dog in heat:
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Keep your dog away from male dogs. This means no visits to dog parks, walks in busy areas, or letting them loose in the backyard, where they could come into contact with an intact male. Keeping them isolated helps avoid unwanted pregnancies.
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Confine your dog when you’re away. Use crates, small rooms, or other confined areas to restrict access and keep them safe.
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Use doggy diapers and pants. These can help avoid spotting in the house during heavier discharge.
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Increase potty breaks. Take your dog outside more frequently to allow for urination and dischargeCleanup any accidents right away with enzymatic cleaners.
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Groom often. Keep the area around your dog’s tail and rear end clean by gently wiping with unscented baby wipes or a warm, wet cloth.
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Watch their diet. Feed a high-quality food and avoid giving extra treats that could cause gastrointestinal upset.
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Exercise appropriately. Take care not to overwork your dog, but provide adequate exercise for behavioral outlet.
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Give them space. Your dog may seem more easily agitated or aggressive, so give them space and supervise interactions.
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Talk to your vet about medication. There are some medications that can help shorten heat cycles or suppress signs of heat.
Keep a close eye on your dog and contact your vet if you have any concerns about their behaviors or health while in heat. With proper management, you can get through this time smoothly.
Health Considerations
A dog’s heat cycle can impact her health in several ways. Here are some things to look out for:
Pyometra – This is a bacterial infection of the uterus that typically occurs during diestrus. Symptoms include lethargy, vomiting, excessive thirst, and discharge from the vulva. Pyometra can be life-threatening if left untreated, so dogs showing these signs during diestrus should see a vet right away.
Mammary cancer – Dogs who aren’t spayed have a significantly higher risk of developing mammary tumors. The risk increases with each heat cycle. Spaying dogs before their first heat virtually eliminates this risk.
Pseudopregnancy – Some dogs experience false pregnancies after heat. They show mothering behaviors like swollen teats, nesting, and appetite changes. This isn’t harmful but can persist for up to a month if not addressed. Consulting a vet can help.
Urinary incontinence – Hormonal changes during heat can temporary impact sphincter control and cause some urine leakage. This usually resolves after the heat cycle ends. Seek vet advice if it persists.
Vaginitis – The swollen vulva during proestrus and estrus can be prone to infection. Signs include bloody, mucus-like, or smelly discharge. Antibiotics may be needed to clear up the infection.
When to See the Vet
While heat cycles are a natural part of a healthy dog’s life, there are times when you should consult your veterinarian. If your dog is experiencing her first heat unusually early or late according to her breed standards, you’ll want to have your vet examine her to check for underlying health issues. Dogs typically go into heat for the first time between 6-24 months. Smaller breeds reach sexual maturity sooner than larger breeds.
You should also contact your vet if your spayed female dog shows signs of heat, as this could indicate issues with the spay surgery or retained ovarian tissue. Other reasons to seek veterinary attention include:
- Extreme lethargy or lack of appetite
- Vaginal discharge that’s bloody, purulent, or has a foul odor
- Abnormal heat cycles occurring too frequently or too infrequently
- No interest from male dogs during the heat cycle
An irregular or abnormal heat cycle can sometimes be a symptom of more serious medical conditions like thyroid disorders, infections, or reproductive cancer. Your vet can run tests to determine if there’s an underlying issue causing the changes in your dog’s cycle. It’s always better to be safe than sorry when your furry friend’s health is on the line.