Dog in Heat: How To Tell and What to Do

When a female dog is “in heat,” it means she is ovulating and can breed and get pregnant. Dogs can go into heat when they are as young as 6–8 months of age, which means if they go into heat and have sex with a male dog, then they can get pregnant, even if they themselves are growing still.

The first heat cycle often is missed by pet parents, which is why many veterinarians advocate for spay surgery at 6 months of age to prevent unwanted pregnancies. Heat cycles vary depending on the dog’s age, size and breed. Small dog breeds can cycle every three to four months, medium and large breeds typically cycle every six months, and giant breeds may only cycle every six to 12 months. Older female dogs may cycle less often than younger dogs. Bleeding during proestrus typically lasts around seven days.

There are four stages, or heat periods, in a dog’s heat cycle: proestrus, estrus, diestrus and anestrus.

1. Proestrus is the stage that many people recognize the signs of a dog in heat. Proestrus typically lasts around seven days. During proestrus, male dogs are attracted to a female, but she is not receptive to them. In proestrus, there is swelling of the vulva and usually bloody vulvar discharge.
2. Estrus is the next stage, and it is during this estrus phase that a female dog is fertile and accepts a male dog’s advances. Estrus typically lasts nine days. The vulva is still swollen, though maybe less so, and there is less bloody discharge.
3. Diestrus lasts around eight weeks, and the female is no longer fertile or receptive to males. During this time, the vulva returns to normal size and discharge dries up.
4. Anestrus defines the time period between diestrus and proestrus. Anestrus lasts around three to five months depending on the size and age of the dog. Your dog’s body is resting at this time and preparing for the next heat cycle.

There are behavioral clues and physical symptoms of a dog in heat, which can include:

• Swollen vulva and bloody vaginal discharge
• Increased moodiness, growling at humans or picking fights with other dogs in the household, especially other unspayed female dogs
• Decreased or increased interest in human interactions
• Increased interest in roaming or getting out of the yard (to look for male dogs to mate with)

If you have an unspayed female dog who is experiencing heat cycles, then you must prepare ahead of time to prevent unwanted pregnancies, bloody messes, escapes or aggression. Here are some best practices:

• Use your phone or a paper calendar to track your dog’s heat cycles. On your phone, record the day your dog’s heat cycle started, and then set a reminder for 6 months in the future with a one-week alert ahead of time so you know it is coming.
• If you have an indoor dog or you just don’t want her leaving a bloody mess, then keep some dog diapers on hand. As with human babies, you can get washable diapers, like Pet Parents washable dog diapers, or disposable diapers, like Simple Solution disposable female diapers. Alternatively, you can purchase human diapers and make them dog-friendly by cutting a hole for her tail.

• If your dog has a hard time getting along with other canines while in heat, or if she tries to escape during her heat, then you might want to consider separating her in a secure area until she is done. You can accomplish this simply by using a gate like Regato’s walk-through pet gate to keep her contained in another room.

What can you do when a dog is in heat to prevent pregnancy? Try these tips:

• Watch her closely. When a dog is in heat, her only thought is to breed, and she will often do whatever it takes to find a mate. It’s important to keep her supervised at all times or contained in a crate or other secure enclosure that she cannot get out of and other dogs cannot get in. There have been reports of dogs climbing fences to escape and mate, and even getting pregnant through chain link fences, so make sure that enclosure is secure!
• Keep male dogs away. If you have male dogs that have not been neutered, they need to be kept separate from the female dog. It’s best if you can board the male dogs or have them stay at another house during the heat cycle. If that’s not an option, make sure there are two barriers (doors or gates) between the dogs at all times.
• Consult your vet in emergencies. If your dog accidentally mates during her heat cycle, there is a ‘morning after’ injection that will terminate an unwanted pregnancy.
• Close the windows. Male dogs can detect female dogs in heat from over a mile away. By closing the windows, you contain her ‘perfume’ to the house.
• Take caution with walks. It’s not recommended to take dogs in heat on walks, because of the risk of attracting male dogs. If you must take her out, make sure she is on a secure leash, and bring a spray bottle filled with water to ward off any would-be wooers.

The most important thing to remember when a female dog is in heat is that if she is around an unfixed male dog, she can get pregnant. She wants to breed, and she might be grouchy. So how can you help your dog in heat? Use these tips:

• Make sure she is kept in a secure enclosure or house, separate from other dogs. Contact with unneutered male dogs can lead to unwanted pregnancy, and even contact with spayed or neutered dogs can result in hormone-related aggression.
• Use doggie diapers to keep messes to a minimum, and give her what she wants, whether it is attention or space.
• Make sure she has her own food bowl, water bowl and bedding in her space.
• If you intend to breed her, then this is the time. Talk with your veterinarian about best practices for breeding.
• If you plan to spay your dog, wait until one month after her heat cycle ends.
• Let your dog tell you how much interaction she wants with you—let her come to you, otherwise, give her space.

With proper attention and tools, your dog’s heat cycle can be easy to manage. Schedule an appointment with your veterinarian if you notice that your dog’s heat cycle is irregular, if there is extended bleeding or discharge, if you think your dog might be pregnant, or if your dog’s behavior becomes abnormal.

Heat cycles in dogs range from every three months to every 12 months, depending on the dog’s age, size and breed.

A dog is said to be in heat when they are in the proestrus and estrus stages of their reproductive cycle; proestrus and estrus last anywhere from one to three weeks in most dogs. During proestrus and estrus a dog will have bloody discharge from the vulva, and during estrus, a dog can get pregnant. 

Proestrus and estrus, the heat phases during which a dog has bloody discharge, can last between one to three weeks.

The most important thing to remember when a female dog is in heat is that if she is around an unfixed male dog, she can get pregnant. To prevent pregnancy in your dog in heat, keep her in a secure enclosure with her own food bowl, water bowl and bedding, apart from other dogs. Use doggie diapers to keep messes to a minimum, and unless she initiates interactions with you, give her space.

Typically, female dogs will have a swollen vulva and bloody vaginal discharge when they are in heat. Sometimes, these signs are not apparent even when a dog is in heat. When this happens, it is said that the dog had a silent heat cycle.

When a dog is in heat, the uterus is big, bloody and fragile due to hormones. This makes the surgery more difficult, dangerous and expensive. Unless medically necessary, do not schedule your dog to be spayed while she is in heat.

If your pup is in heat, it’s important that you take the time to make sure she’s safe and comfortable. And be sure to discuss with your veterinarian about spay surgery and how it can benefit your pet.