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Do dogs in heat get sick? (Or get Diarrhea?)

Female dogs who haven’t been spayed will naturally go into heat. This isn’t something to be concerned about, but some dogs don’t feel well when they are in heat. However, some dogs do get sick and need to visit the vet. 

Do dogs in heat get sick?

A dog in heat can feel mildly ill. However, if they are severely sick, they may have another condition causing symptoms. 

The Heat Cycle

The heat cycle begins with proestrus. This is when you’ll likely notice that your dog is in heat. It lasts from 7 to 10 days, with 9 days being the average length. 

During this time, the vulva swells. You may notice personality changes as well. Some dogs act the opposite of their normal behavior, while some are only a little different. It’s common for her to be clingy or standoffish during this time. 

You may notice appetite changes as well. Some dogs eat very little, while others seem famished. Bleeding will also begin in this stage. 

When a dog attempts to investigate her, she will sit down or put her tail between her legs. This is her way of saying she’s not ready to breed yet. 

The next stage is estrus. This is when the female is actually fertile. You’ll notice flirtatious behavior with male dogs. She may wave her tail as a way of “flagging” potential mates. This is actually a scent cue instead of a visual one. With her tail held high, the male can smell that she is ready to breed. Bleeding still occurs, but it is lighter. The vulva softens to allow penetration. 

Diestrus is the next stage of the heat cycle. Vulva swelling gradually subsides and hormone levels begin to normalize. Bleeding will once again become bright red before stopping. If she is pregnant, diestrus remains until birth. 

If she wasn’t bred, anestrus occurs. The heat cycle is over. It will be 5-11 months before a new cycle occurs. 

Hormonal Changes

Hormonal changes are responsible for many symptoms of heat, including behavioral changes and potential nausea. 

During proestrus, the female’s estrogen levels rise much higher than normal. Males will be attracted to her hormones and pheromones, but she isn’t ready to mate.  

During the estrus cycle, estrogen drops and progesterone rises. The female is receptive to males during this time. 

During diestrus, estrogen levels remain low. Progesterone reaches peak levels at 3-4 weeks after diestrus begins, and then returns to baseline at the end of the diestrus cycle. 

Nausea and Vomiting

Nausea and vomiting are common problems when a female is in heat. High hormone levels can cause gastrointestinal issues themselves. When the hormone levels begin to fall, they are processed in the liver and then sent to the gut. The gut expels them in waste. However, this can also cause stomach upset. 


Pyometra usually occurs 3 to 5 weeks after the heat cycle. It’s an infection of the female’s reproductive organs. Signs include vomitting, abdominal swelling, lethargy, and fever. 

It’s a life threatening condition that often requires emergency spay surgery. If your dog is vomiting several weeks after her heat cycle, take her to the vet for a check-up. 


A dog’s heat cycle has the potential to end with pregnancy if a male is allowed to breed her. If your dog is pregnant, she may experience morning sickness. This usually occurs during the 3rd or 4th week of pregnancy and lasts a few days to a few weeks. 

She may also be a bit tired or lethargic. Appetite changes can occur, with a period of less appetite followed by increased appetite as the puppies begin to grow inside her. 

Caring For a Dog With Vomitting During Heat

There are a few things you can do to settle your dog’s stomach when she’s in heat. Try feeding them a few crackers first thing in the morning. The carbohydrates can help soak up extra hormones in the stomach. 

You can also give peto bismal. The recommendation is one teaspoon per 10 pounds of body weight given every 6-10 hours. 

Ensure that they are staying hydrated. If they are vomitting frequently, you may need to give them pedialyte to replace lost electrolytes. 

If vomiting is frequent or continues for more than a few days, you’ll need to take them to the vet. Other illnesses, including pyometra, can cause vomiting in female dogs. Your vet can also prescribe medication for nausea if needed. 

Do dogs get weak when in heat?

Some dogs get weak or lethargic when in heat. Others get bursts of energy. This is due to the hormonal changes of the heat cycle. Many women experience fatigue during their menstrual cycle for similar reasons. 

Caring for a Dog With Fatigue During Heat

Caring for your dog’s fatigue or weakness when in heat is as simple as listening to their body. Let them get plenty of rest. Give her a quiet comfortable place to nap as needed.

Exercise is still important, but you may need to keep it to short outings instead of long walks or active play sessions. 

When to Worry

Your dog may exhibit many strange behaviors when in heat that are perfectly normal. However, if they are so weak that they barely get out of bed, this is a concern. 

If they have severe fatigue or loss of appetite, consult your vet. Some weakness or fatigue is normal, but your dog should still be able to perform her daily functions. 

Do female dogs get diarrhea when in heat?

Yes, they can get diarrhea when in heat for the same reason vomiting. However, diarrhea is also a symptom of pyometra. Other illnesses, including parasites, can also cause diarrhea. 

Is It Heat or Parasites? 

If your dog has diarrhea, you may be wondering if it’s caused by her heat cycle or parasites. Symptoms of parasites include vomiting, diarrhea, and butt scooting. Weight loss and abdominal swelling can also indicate a parasite problem. Dogs with severe parasite infection often cough as well. 

One way to confirm parasites is to check your dog’s poop. If you see what looks like white strings, these are parasites. However, your dog can have parasites that aren’t visible in poop, so a lack of spotting them doesn’t rule them out. 

When to See the Vet

If this isn’t your dog’s first heat cycle, you should be familiar with their symptoms while in heat. If you notice symptoms different than expected, take them for a check-up. 

If it’s your dog’s first heat cycle, it’s wise to get an examination as well. Your vet can update you on her status as well as check for any health conditions. 

If your dog is experiencing fever, this is a sign to take them to the vet. If diarrhea or vomiting lasts more than a few days, they will need an examination as well.