The Stages of the Dog Heat Cycle

By Deb Haines

Most dogs come into heat twice per year, or about every six months, although the interval can vary between breeds and from dog to dog. Small breed dogs may cycle three times per year, while giant breed dogs may only cycle once every 12 months. When young dogs first begin to cycle, it is normal for their cycles to be somewhat irregular. It can take up to two years for a female dog to develop regular cycles.

The canine estrous (reproductive) cycle is made up of 4 different stages. These are proestrus, estrus, diestrus, and anestrus. Each stage has differing signs related to behavior, physical or clinical changes, hormonal changes, physiologic changes, and cytologic (vaginal smear) changes. The following is a general description of the various stages and the changes associated with each stage.

The 4 stages

Proestrus is the stage that most owners start noticing changes and when we say “the dog is in heat”. This stage lasts for an average of 9 days, but can range anywhere from 0-27 days. This is when males dogs will be attracted to the female, but she will not be receptive. The estrogen levels will peak and the follicles will develop. The vulva will usually be swollen with a blood tinged discharge.

Estrus is the stage when the female is receptive to the male. This stage will last an average of 9 days based on behavioral signs, but can range from 4 to 24 days. The fertile period occurs during this time. The vulva is enlarged, but softens a little. There is a decrease in the blood in the vulvar discharge. Estrogen levels are dropping and progesterone levels are starting to increase.

Diestrus is the stage following estrus and the female is no longer receptive to the male. This stage lasts for about 2 months. Estrogen levels are low, while progesterone peaks 3 to 4 weeks after the start of diestrus and then declines to basal levels by the end of diestrus. This increase and then decrease in progesterone will occur regardless of if the dog is pregnant

Anestrus is the time between diestrus and the next proestrus. This stage will last for about 4 months, though certain breeds can be much longer. The vulva is no longer swollen, there is no vaginal discharge. The body uses this time to allow the uterus to prepare for the next possible pregnancy

When Does A Dog Experience Her First Estrus?

First estrus generally occurs when an unspayed female dog is between six and 24 months old. It tends to occur earlier for small-breed dogs nd later for large-breed dogs.

How Long Does a Dog Stay in Heat?

The time during which male dogs are attracted to a female dog is variable, approximately 18 days. However, females are receptive to males for only about half of this time.

How Can I Prevent My Dog From Going Into Heat?

It is highly recommended that you get your female dog spayed, not only to prevent estrus and accidental pregnancy, but to protect her against breast cancer and diseases of the reproductive system.

At What Age Can I Have My Dog Spayed?

Generally, a veterinarian can spay a dog when she is as young as two months old. However, it is best to consult with your veterinarian for specific recommendations regarding the best time to spay your dog.

Signs That Your Dog Is in Heat

  • Swollen vulva. This non-painful swelling typically occurs a few days before any discharge or bleeding will occur.
  • Bleeding. A bloody discharge from your dog is usually the first sign of heat you will notice.
  • Mounting behavior. Your dog may try to mount other dogs, objects, or your leg.

When your dog is in heat she gives off pheromones which a male dog can smell from miles away. Male dogs will become interested in her and may fight over her.

When in heat, many dogs become restless. The hormones may cause them to become more anxious, and they become focused on searching for a mate. Your dog may also be annoyed by the discharge.

It is not uncommon for female dogs in heat to have loose stools, see your vet if you see any worrisome signs accompanying like diarrhea or the diarrhea gets severe. Of course, the diarrhea can be due to other reasons (eating something inappropriate, sudden diet change, presence of parasites, viruses etc) which may need treatment. please communicate with your hands on veterinarian.

Some dogs do get an upset stomach the moment they go in heat. The culprit may be those hormonal changes that can mess things up in the digestive tract in sensitive dogs. These can lead to mood changes that can cause mild gastro-intestinal upset. The female dog may also lose their appetite temporarily as she is so focused in searching for a mate.

Please keep in mind why we recommend spaying your pet

Your female pet will live a longer, healthier life.
Spaying helps prevent uterine infections and breast cancer, which is fatal in about 50 percent of dogs Spaying your pet before her first heat offers the best protection from these diseases.

Your spayed female won’t go into heat.
While cycles can vary, female felines usually go into heat four to five days every three weeks during breeding season. In an effort to advertise for mates, they’ll yowl and urinate more frequently-sometimes all over the house!

Spaying will NOT make your pet fat.
Don’t use that old excuse! Lack of exercise and overfeeding will cause your pet to pack on the extra pounds-not spaying. Your pet will remain fit and trim as long as you continue to provide exercise and monitor food intake

Your pet doesn’t need to have a litter for your children to learn about the miracle of birth.
Letting your pet produce offspring you have no intention of keeping is not a good lesson for your children-especially when so many unwanted animals end up in shelters. There are tons of books and videos available to teach your children about birth in a more responsible way.

FOOD FOR THOUGHT…..Spaying and neutering helps fight pet overpopulation.
Every year, millions of cats and dogs of all ages and breeds are euthanized or suffer as strays. These high numbers are the result of unplanned litters that could have been prevented by spaying or neutering. Spaying and neutering packs a powerful punch in reducing the number of animals on the streets.


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