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Why Are My Dog’s Nipples Enlarged After Heat? Asked & Answered

Why Are My Dogs Nipples Enlarged After Heat

Having your dog go through heat can leave you with many questions, including “why are my dog’s nipples enlarged after heat?” Whether it’s your dogs first heat before you spay, or you are interested in breeding, changes in her body are inevitable. And, it’s essential to know what’s normal and what to expect.

Of course, physical changes can include swelling of the mammary glands and increased blood flow to the area, resulting in enlarged nipples. These changes are often uncomfortable and possibly painful to some dogs. Ensuring your dog has a comforting bed in a quiet resting space is vital.

To answer your question, we have consulted our expert source, Canine Reproduction: The Breeder’s Guide by Phyllis Holst. Let’s take a closer look at the topic to understand why it happens.

However, they can also be a sign of other underlying conditions. So, it’s important to know when to see a vet.

9 Common Causes of Enlarged Nipples in Dogs After Heat 

8 Common Causes of Enlarged Nipples in Dogs After Heat 

It is natural for a dog’s nipples to stay enlarged for a couple of weeks after heat. However, if the enlargement persists, there are other possible causes. 

Several factors can contribute to a dog having enlarged nipples after heat. These are the following most common causes:

1. Hormonal changes

During the heat cycle, a dog’s levels of estrogen and progesterone fluctuate. This plays a significant role in preparing the mammary glands for potential pregnancy and milk production. 

These hormonal changes can increase the size and number of milk-producing cells within the mammary glands, resulting in nipple enlargement.

In our article on how many litters a dog can have, we discuss some of the risks that come with a dog that is heat. The main one is that a heat without pregnancy means her system is flooded with progesterone for much longer. Progesterone is inflammatory to the uterus, potentially leading to deadly uterine infections called pyometra. These hormones also increase the risk of cancer. So, we encourage you to spay your as soon as she reaches a suitable age.

2. Pregnancy

Perhaps the most obvious reason that a female dog’s nipples grow bigger after being in heat is just that she is pregnant. About 3 weeks after conception, a dog’s nipples will start to become larger and they may also change color. The nipples at the back, in particular, may become distended and become a lighter pink or reddish color.

Even if you did not breed your dog, remember that dogs can be phenomenal about climbing fences to get to female dogs in heat. A male dog that wants to mate is a constant risk. To avoid an unplanned pregnancy in a young female, one needs to take many steps to keep her isolated from potential suitors. Once she is old enough, it’s best to spay her as soon as possible.

Remember, part of responsible dog ownership is avoiding bringing unplanned puppies into the world that may contribute to the shelter population later on. Is you suspect your dog is pregnant, you can see the video below for how to examine your dog at home.

3. Pseudopregnancy 

Pseudopregnancy, also referred to as false pregnancy or pseudocyesis (also called a phantom pregnancy), is a condition that can occur in female dogs. It occurs when a dog’s body goes through physiological changes that mimic an actual pregnancy, despite the dog not being pregnant.

During pseudopregnancy, a dog’s hormonal levels, particularly progesterone and prolactin, can become imbalanced, leading to symptoms that resemble those seen in pregnant dogs. One of the noticeable changes is the enlargement of the nipples. Other signs of a false pregnancy in dogs include:

  • Fluid retention (making her midriff look swollen as if she is pregnant)
  • Changes in nipple color
  • Vomiting
  • Lethargy
  • Lack of appetite

4. Mastitis

Mastitis is a condition characterized by inflammation or infection of the mammary glands in female dogs. While it can occur at any time, the hormonal changes during and after the heat cycle can increase the risk of developing mastitis.

5. Mammary tumors

While less common, mammary tumors can cause enlarged nipples in dogs. Mammary tumors are abnormal growths that develop within the mammary gland tissue. They can occur in intact and spayed female dogs, although intact females have a higher risk. Spaying your dog is the best way to reduce her risk of breast cancer.

6. Mammary gland hyperplasia

Mammary gland hyperplasia refers to the excessive growth of mammary gland tissue in female dogs. Hormonal imbalances or responses within the body are typically the cause. 

Mammary gland hyperplasia can result in enlarged nipples and can occasionally be mistaken for tumors as it can look pretty similar.

7. Infections or abscesses

Infections in the mammary glands, particularly bacterial infections, can result in inflammation, swelling, and enlargement of the nipples in dogs. These infections can cause discomfort and require veterinary attention for appropriate diagnosis and treatment.

8. Trauma or injury

Any trauma or injury to the mammary glands or the surrounding tissues in dogs can result in localized inflammation and subsequent nipple enlargement. 

9. Medications or side effects

Certain medications used on dogs, including hormone therapies and certain contraceptives, can impact hormone levels, which in turn can cause changes in the mammary glands, including nipple enlargement.

Natural Causes of Nipple Enlargement In Dogs

Natural Causes of Nipple Enlargement In Dogs

The Canine Heat Cycle

A canine heat cycle directly impacts the size and appearance of a female dog’s nipples. This cycle consists of various stages, and knowing what is considered normal is essential. After the heat cycle, the nipples may not only get bigger, but they may also change color, becoming a light pink or even reddish hue.

What Are the Stages of the Canine Reproductive Cycle?

The female dog’s reproductive cycle, or the estrous or heat cycle, involves hormonal changes that impact her reproductive organs and nipples. The cycle consists of four main stages: proestrus, estrus, diestrus, and anestrus. If your dog is in heat, also be sure to read about what to do to help relieve her cramps.

What Should My Dog’s Nipples Look Like During Each Stage Of Her Reproductive Cycle?

  • Proestrus: During proestrus, the nipples may become slightly enlarged or swollen. They may also appear more prominent than usual. 
  • Estrus: In estrus, the nipples typically remain enlarged and may continue to be sensitive. They may appear more engorged due to increased blood flow to the mammary glands. This is when the dog is fertile. We address this further in our article on if dogs can fall pregnant when she is not in heat.
  • Diestrus: During diestrus, the nipples may gradually return to average size and sensitivity. The color of the nipples tends to fade back to pale pink or a color similar to the dog’s normal pigmentation. 
  • Anestrus: In anestrus, the nipples should appear normal, similar to their pre-heat cycle state. They should be neither enlarged nor sensitive. 

Note: It’s important to remember that individual variations exist, and the appearance of a dog’s nipples can differ depending on factors such as breed, age, and overall health.

What Should I Do If My Dog’s Nipples Stay Enlarged Well After Heat?

If your dog’s nipples remain enlarged well after the estrus stage, it is advisable to consult a veterinarian. Prolonged or persistent enlargement of the nipples can indicate an underlying health issue that requires attention.

  • Schedule a veterinary appointment: Contact your veterinarian and explain the situation. They will be able to guide the next steps. 
  • Veterinary examination: During the appointment, the veterinarian will thoroughly examine your dog, focusing on the mammary glands and nipples. 
  • Diagnostic tests: Depending on the findings during the examination, the veterinarian may recommend additional tests such as blood work, imaging (such as ultrasound or X-rays), or further sampling of the nipple tissue. 
  • Follow veterinary recommendations: Once you have a diagnosis, your veterinarian will provide appropriate treatment options or further recommendations based on the specific condition. 

Note: It’s essential to take prompt action and seek veterinary attention if you notice persistent enlargement of your dog’s nipples. Early detection and proper treatment can improve outcomes and help ensure the well-being of your dog.

Frequently Asked Questions

Why are there lumps in my dog’s nipples after her first heat?

Enlarged nipples and small lumps in a dog’s nipples after her first heat are typically a normal response to hormonal changes during the heat cycle. If the lumps do not subside along with the size of the nipple, you should seek a veterinary diagnosis.

How long do dogs’ nipples stay enlarged after heat?

The duration a dog’s nipples stay enlarged after heat can vary. In most cases, the nipples may remain enlarged for a few weeks following the heat cycle. However, it’s important to note that individual dogs can exhibit different timelines. If a dog has been pregnant, and particularly if she has nursed, her nipples will likely never go back to their original size.

Is it normal for a dog’s nipples to swell after heat?

It is very normal for a dog’s nipples to swell after heat as her body adjusts to fluctuating hormones. However, it is also the most common sign of a pregnancy or phantom pregnancy. So, if you notice swollen nipples and other suspicious changes, it’s best to see a vet to rule out underlying problems.

Can a dog’s nipple swell if not pregnant?

After heat, the progesterone levels in a female dog’s body drops; after they were in heat, the hormone prolactin rises naturally, causing the mammary glands and nipples to swell. This natural rise of prolactin causes the nipples to swell even if she is not pregnant.

Final Thoughts

It is normal for a dog’s nipples to remain enlarged for a couple of weeks following the heat cycle. It is a result of hormonal changes that occur during the cycle. The increased levels of estrogen and progesterone can cause the mammary glands to remain enlarged during this period.

The cause is often increased blood flow to the area and natural localized swelling. However, it’s essential to know that nipple enlargement after heat can also indicate other underlying conditions. The most obvious reason for enlarged nipples is a pregnancy, planned or unplanned.

Pseudopregnancy, mastitis, mammary tumors, mammary gland hyperplasia, infections, trauma, or certain medications can all contribute to nipple enlargement in female dogs.

It is essential to monitor your dog’s condition closely and seek veterinary attention if the nipple enlargement persists beyond the expected timeframe.


Tamsin De La Harpe


Tamsin de la Harpe has nearly two decades of experience with dogs in rescue, training, and behavior modification with fearful and aggressive dogs. She has worked closely with veterinarians and various kennels, building up extensive medical knowledge and an understanding of canine health and physiology. She also spent two years in the animal sciences as a canine nutrition researcher, focusing on longevity and holistic healthcare for our four-legged companions.

Tamsin currently keeps a busy homestead with an assortment of rescue dogs and three Bullmastiffs.

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