- Unspayed female dogs can have their first heat cycle anywhere between 6 and 15 months of age.
- During heat, which happens every six months or so and lasts a few weeks, your dog can get pregnant.
- Spaying your dog prevents pregnancy, lowers her cancer risk, and may even lengthen her lifespan.
If you got your female dog from a pet store or breeder, or adopted her from a shelter or rescue at a very young age, chances are she probably isn't spayed. At some point, then, your pup will inevitably be in "heat" — the part of her reproductive cycle when she's open to mating and can get pregnant.
Heat is sometimes referred to as a "dog period" because of the bloody vaginal discharge, but it's important to note that dogs don't menstruate in the same way human females do. They do, however, have cycles during which they experience a surge and then decline in estrogen, and their ovaries release the eggs. Heat is the stage of this process when your dog ovulates.
Male dogs can only impregnate female dogs who are in heat, says Dr. Megan McCarthy, a staff veterinarian at Best Friends Animal Society. That's why it's essential to pay attention to signs that suggest your dog is in heat.
Here's everything to know about dogs in heat — when and how often it happens, how long it lasts, and how to tell it's happening.
How often does it happen?
Most dogs will have their first heat cycle between six and 15 months of age. This can vary depending on the dog's size and breed.
According to Dr. Ole Alcumbrac, veterinarian and owner of White Mountain Animal Hospital, dogs typically go into their first heat when they've reached about 70%-80% of their maximum body weight. Larger breeds tend to start their heat cycles much later than smaller breeds, McCarthy says.
Dogs usually go into heat twice a year, or every 6 months or so, McCarthy says, and small dogs tend to go into heat more frequently than large dogs. Smaller breeds may cycle three times a year, but very large breeds may only cycle once a year.
Heat cycles tend to be pretty consistent, so if your dog has two heat cycles 6 months apart, you can expect that to continue. However, it can take up to two years for your dog to experience regular cycles. Additionally, keep in mind that the length of time between heat cycles can increase as a dog gets older.
What are the signs?
Identifying the signs of your dog's heat cycle can help you avoid puppies, for one thing, but it can also help you care for your dog properly.
These signs can indicate your dog is in heat.
Early signs
The first signs of heat appear during "proestrus," when your dog's reproductive tract prepares for ovulation. During proestrus, male dogs may seem more attracted to your dog, but she likely won't be receptive to mating. Even if she does mate with a male dog, she can't become pregnant during this stage.
You may notice the following during proestrus:
- Swelling of the vulva
- Bloody vaginal discharge
- Holding or tucking her tail closer to her body
- Increased clinginess
- Changes in appetite
- Aggression toward male dogs
Alcumbrac says vulva swelling is usually the first symptom, followed by blood-tinged discharge.
Active heat signs
The "estrus" stage is when your dog is in active heat and able to be impregnated. You may notice the following signs during estrus, according to Dr. Amy Attas, a veterinarian and founder of City Pets:
- Less discharge that's lighter/pinkish in color
- Less swollen vulva
- More receptiveness and friendliness toward male dogs
- Increased vocalizing, especially moaning, whining, yowling, and crying
- More aggression toward female dogs
- Restless or nervous behavior
- Peeing more frequently than normal
- Increased attraction and attention from male dogs
- "Flagging" — lifting her rear toward male dogs or moving her tail to the side
Attas says it's also not uncommon for female dogs to urinate small amounts on various objects in the home or outside while in heat. That's because during estrus, their urine contains pheromones and hormones that signal their reproductive state to male dogs.
How long does heat last?
The heat cycle lasts for about 18-21 days.
According to Alcumbrac, proestrus averages about 2-11 days, and estrus usually lasts 3-5 days but can be as long as 11 days.
The length can vary based on your dog's breed, size, and age, but once your dog begins to have regular cycles, you can expect them to stay in heat for roughly the same amount of time.
What should I do?
Your dog may require a little extra TLC during heat. Fluctuating hormone levels can have a big impact on her physically and behaviorally, which is why McCarthy advises giving her plenty of attention and comfort.
To care for your dog during heat, you can:
- Take her on frequent short walks. She may need to pee more often while she's in heat, and light exercise can also help her release pent-up nervous or aggressive energy. Consider taking walks earlier in the morning or later in the evening, when there's less dog traffic in your neighborhood. Never force your dog to take a walk if she seems tired — instead, let her rest.
- Offer chew-resistant toys to distract her and help relieve stress.
- Avoid scolding or shaming your dog for any messes due to bloody discharge. Speak in a gentle, reassuring voice.
- Make sure your dog drinks plenty of water and eats well.
- If you have multiple dogs, make sure she has her own food bowl, water bowl, and bed to avoid fights.
- Make time to pet her, massage her, and brush her coat, all of which can be soothing and calming.
- Give her plenty of space and allow her to initiate cuddles and interactions.
If you use doggy diapers, McCarthy says it's important to change them often — at least every three to four hours — to prevent skin irritation and urinary tract infections.
Keeping your pup away from unneutered male dogs is crucial if you're trying to prevent pregnancy, says Attas. McCarthy suggests avoiding dog parks, group training events, and other events involving other dogs while yours is in heat.
Never leave your dog alone outside, and always keep her on a leash when going for walks. You may even want to keep windows closed to prevent male dog visitors from showing up at your house.
When to get your dog spayed
Getting your dog spayed as soon as possible is the best way to prevent your dog from getting pregnant, especially if they spend a lot of time around other dogs, McCarthy says.
The American Animal Hospital Association recommends spaying before your dog's first heat cycle:
- Between five to six months of age for breeds that weigh less than 45 pounds when fully grown
- Between 5-15 months for breeds that weigh more than 45 pounds when fully grown
"We usually want to allow the larger breeds to grow more before spaying because this procedure can alter the way their bones develop," Alcumbrac says.
If you're not sure about the appropriate time to spay your dog, consult your veterinarian.
Benefits of spaying
Each year, approximately 3.1 million dogs enter U.S. animal shelters. Due to overcrowding, approximately 390,000 are euthanized. So unless you have a specific plan for puppies, spaying your dog is the best way to prevent further unnecessary premature dog deaths.
Experts also say spaying can have multiple health benefits for your dog. In fact, a 2013 study found that the life expectancy of spayed female dogs was 26.3% longer than that of unspayed dogs.
One reason being that spaying reduces your dog's risk of breast cancer and pyometra (a potentially fatal uterine infection that occurs as a result of hormonal changes in the reproductive tract).
Breast cancer is the most common type of tumor in unspayed female dogs. In fact, about half of mammary gland tumors in dogs are cancerous.
But spaying your dog reduces the production of hormones that can contribute to the growth of these mammary gland tumors. That's why dogs spayed before their first heat have only a 0.5% risk of developing mammary cancer.
This risk increases to 8% if they're spayed between the first and second heat cycles and jumps to 25% if they're spayed any time after their second heat.
Lastly, spaying your dog can reduce certain behavioral problems, including:
- Aggression
- Roaming
- Excessive vocalizing
- Urine marking
Insider's takeaway
All unspayed female dogs go into heat — a stage in their reproductive cycle when they're open to mating and able to get pregnant. If you can recognize the early signs, you have a better chance of preventing your dog from getting pregnant.
When you notice signs of heat, you can reduce the chances of unwanted pregnancy by always using a leash when taking them outdoors and keeping them away from dog parks or other areas that may have unneutered dogs.
In addition to protecting your dog from getting pregnant, you'll also want to make it a point to provide her with plenty of comfort.
Remember: While spaying is a personal decision that only you as the owner can make, it can offer a range of benefits for both you and your beloved pup.