Do Dogs in Heat Get Sick? (4 Stages of Heat + How to Care?)

If you are the owner of an unspayed female dog, you probably have questions about how to care for your dog during her heat cycle. You might wonder if your dog will get sick during her heat cycle.

A dog goes into heat twice a year, for 2-3 weeks. During this time, you will notice physical and behavioral changes. Some changes might make your dog appear sick, but they are a natural part of the heat cycle. Your dog can still get sick while in heat, but being in heat will not make it sick.

Your dog is more sensitive when in heat and can exhibit unpredictable behaviors, so it’s essential to take special care of your dog during this time. Read on to find out!

What Is the Heat Cycle?

The scientific name for the heat cycle is the estrus cycle. There are four stages of the estrus cycle:

  • Proestrus
  • Estrus
  • Diestrus
  • Anestrus

The fertile part of the heat cycle is estimated to last about 21 days, but every dog is different. Some dogs’ heats are much longer, while others are much shorter.

Let’s look at the four stages of the heat cycle to understand what to expect during each.

The Proestrus Stage

This is the first stage of the cycle. The dog is not fertile during this stage, but her body prepares to become fertile. You may notice behavioral changes during this stage. You will also see a swelling of the vulva. During this phase, your dog will start to bleed.

The proestrus cycle can last between 3 – 17 days, but the average length is nine days.

Behavioral Changes

Behavioral changes will be different for every dog. Some dogs become very grumpy during the proestrus phase. Some want to hide or will tuck their tail and run away from you. Others become very clingy or affectionate.

Other Changes

Your dog may experience appetite changes. Again, these changes will be different depending on the dog. Some dogs lose their appetite while others become more hungry. Keep an eye on your dog and monitor her closely to ensure she is eating and drinking enough.

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Monitor your dog closely at this time to prevent fights with other dogs.

The Estrus Stage

During this stage, your dog is fertile. You will notice some discharge from her vagina and softening of the vulva. You will detect more behavioral changes during this time. The estrus phase lasts 3 – 21 days, with an average of 9 days.

Behavioral Changes

Your dog might start to “flirt” with male dogs during this time. During the proestrus phase, a female dog will tuck her tail to protect and hide the vulva. Now, however, she will begin to turn her rear toward male dogs and hold her tail up and out of the way to signal that she is ready to mate.

Monitor your dog closely during the estrus phase of the cycle to prevent unwanted pregnancy.

The Diestrus Stage

At this time, the part of the cycle where your dog is fertile ends. This stage lasts between 60 and 90 days. By the end of this stage, the dog is no longer fertile. If the dog is pregnant, you will start to notice pregnancy symptoms.

Behavioral Changes

Your dog will stop flirting with other dogs and may become stand-offish or even aggressive and will no longer be receptive to male attention. If the dog is pregnant, it may become less active, and its appetite may increase.

Other Changes

You will notice a reduction in the swelling of the vulva. If the dog is pregnant, you will notice that the nipples become enlarged. You may also see some weight gain and an enlarged abdomen.

The Anestrus Stage

The anestrus stage is the final stage of the heat cycle. It lasts anywhere from 100 – 150 days. At the end of this stage, the cycle begins again at proestrus.

Behavior Changes

At this point, your dog should return to “normal” behavior and eat and act as expected. If you notice any strange behavior in your dog during this time, it could indicate that your dog is sick.

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What Should I Watch Out For?

Your dog can become sick during heat if you do not watch her closely. If your dog loses her appetite, she may stop eating or drinking, leading to dehydration or severe weight loss. If anxious, she may become self-destructive and damage her coat, claws, or other body parts.

Your dog’s heat cycle doesn’t just affect your dog. It affects all the unneutered male dogs in the nearby area. Male dogs can become so obsessed with your female that they stop eating or drinking. They can also injure themselves trying to get past fences or other barriers.


Pyometra is the primary concern for dog owners whose dogs are in heat. Pyometra is a uterine infection, and it can become severe or even fatal if not treated. Symptoms of Pyometra include vomiting, loss of appetite, lethargy, and fever.

Talk to your vet if your dog is in heat and begins vomiting or displaying any other symptoms of Pyometra. If you do not plan to breed your dog, it’s a good idea to spay her to eliminate the chance of her contracting Pyometra in the future.

How Do I Care for My Dog in Heat?

Although being in heat won’t necessarily make your dog sick, some of the behavioral changes she experiences could put her at risk of becoming sick through dehydration, inactivity, or loss of appetite. Provide plenty of water, feed her regularly, and ensure she has a safe, comfortable place to hide if she needs to.

If you do not want your dog to become pregnant, never leave her unattended during her heat cycle. Even if your dog is well trained, no amount of training can overcome instinct.

Every dog reacts differently to her cycle. Watch your dog closely and talk to your veterinarian about the best way to care for your dog during heat.

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Susan Dorling

I am a pet expert with years of experience working with a variety of animals. From dogs and cats to birds and exotics, I have a deep understanding of their unique needs and behaviors. I am dedicated to helping pet owners provide the best care for their furry friend.