Many pet owners first notice their female dog’s teats or nipples becoming enlarged and wonder if she is pregnant. However, there are several other reasons besides pregnancy that may cause a dog’s nipples to enlarge. This article outlines the key questions around enlarged canine nipples:
- What causes dog nipples to become enlarged?
- How can you tell if nipple enlargement is sign of pregnancy?
- What other conditions may lead to enlarged nipples in dogs?
- When should you take your dog to the vet for nipple enlargement?
- What treatments are available for non-pregnancy related nipple enlargement?
Read on to learn more about the various causes of nipple enlargement in dogs.
Female Dog Heat Cycles
Female dogs go through heat cycles approximately every 6 months once reaching sexual maturity. This occurs around 6-12 months of age. The heat cycle has four distinct stages:
Proestrus – This stage lasts around 9 days. The vulva will swell and bleed. Female dogs will attract male dogs but will not allow mating. Hormone changes cause enlargement of the vulva, uterus and mammary glands which can lead to nipple enlargement.
Estrus – Also known as being “in heat”, this stage lasts around 9 days as well. The vulva remains swollen and bleeding slows down. The female will now allow mating. Ovulation occurs towards the end of this stage, with the peak fertility window being days 10-14 of the cycle.
Diestrus – This stage lasts 60-90 days. If mating did not occur, the heat cycle ends. If pregnancy occurred, this stage continues until birth. The vulva returns to normal size but mammary glands and nipples remain enlarged to prepare for potential nursing.
Anestrus – The resting stage where the reproductive system is inactive. This lasts around 120-150 days until the next cycle begins. Mammary glands and nipples return to normal size if no pregnancy occurred.
Pseudopregnancy
Pseudopregnancy, also known as false pregnancy, is a common condition that occurs in intact female dogs after an estrus or heat cycle. During this time, the dog’s body behaves as if she is pregnant even though conception did not occur. The exact causes are not fully understood but it’s thought to be related to hormonal fluctuations after estrus (see VCAAnimal Hospitals).
Some of the most noticeable symptoms of pseudopregnancy in dogs include physical changes in the mammary glands and nipples. According to PetMD, the dog’s nipples will enlarge evenly during pseudopregnancy, similar to a real pregnancy. The mammary glands will also enlarge and swell, which can be uncomfortable for the dog. In some cases, the dog may even start producing milk from the mammary glands (see PetMD). WagWalking states that you may notice milk leaking from the nipples or be able to express it when gently squeezing the mammary glands.
These nipple and mammary gland changes are caused by the hormones progesterone and prolactin. The physical enlargement occurs as the dog’s body prepares for nursing puppies, even though she is not actually pregnant. Typically, the changes resolve on their own within 2-4 weeks after the start of pseudopregnancy (see WagWalking). However, if the enlargement persists or causes discomfort, veterinary attention may be needed.
Mammary Gland Hyperplasia
Mammary gland hyperplasia is a benign condition where the mammary glands become enlarged or develop lumps, typically around the time of heat in intact female dogs. It’s caused by an increase in circulating hormones like estrogen and progesterone during the heat cycle, which stimulates proliferation of normal mammary gland tissue.
With mammary gland hyperplasia, the nipples may become enlarged and swollen. The skin around the nipples also appears thickened. These changes are not necessarily an indication of pregnancy and can occur in both intact and spayed dogs, though it’s more common in intact females.
According to the BluePearl Specialty and Emergency Pet Hospital, up to 75% of intact female dogs develop mammary gland hyperplasia during their lifetimes. The abnormal tissue growth is usually reversible once hormones return to normal levels after heat. However, frequent or prolonged hormone stimulation can cause hyperplastic tissue to become neoplastic over time.
Mastitis
Mastitis is the inflammation of the mammary glands and nipples (known as the mammary chain). It is most commonly caused by a bacterial infection, usually occurring during lactation. The bacteria, most often Staphylococcus or Streptococcus, enter through openings in the skin or damaged tissue like cracks or wounds. Other causes include trauma to the mammary tissue, milk accumulation, and some systemic diseases. With mastitis, the mammary glands become red, swollen, hard, and painful. The nipples may also become enlarged. According to the VCA Animal Hospitals, the infected glands will become increasingly swollen, inflamed, discolored (frequently red or purple), and painful as mastitis progresses.1
Some common symptoms of mastitis and nipple enlargement in dogs include:
- Swollen, firm mammary glands
- Warm and painful mammary glands
- Enlarged or discolored nipples
- Nipple discharge – may be opaque, bloody, or purulent
- Lethargy, fever, and loss of appetite
- Visible wound on nipple or mammary tissue
Treatment usually involves antibiotics, anti-inflammatories, and warm compresses. In severe cases, the affected mammary glands may need to be surgically removed. Left untreated, mastitis can lead to abscess formation and sepsis.
Mammary Tumors
Mammary tumors (or mammary gland tumors) are common in intact older female dogs that have not been spayed. A veterinarian can typically detect mammary tumors as solid masses or lumps in one or more mammary glands (1). Benign and malignant variants exist, with malignant mammary tumors being the most common type of canine mammary cancer. Dogs with malignant mammary tumors often develop swollen or ulcerated nipples (2).
The most common symptoms of mammary tumors in dogs are (3):
- Solid lump(s) or swelling in the mammary glands
- Enlarged or ulcerated nipples
- Discharge or bleeding from the nipples
- Redness, inflammation, or skin irritation around the nipple
Mammary tumors typically form under the skin of the abdomen or lower chest area. They can range from small, slow growing masses to large, ulcerated tumors. Benign mammary tumors are usually enclosed in a fibrous capsule and don’t spread to other sites. Malignant variants invade surrounding tissue and have potential to metastasize to other areas of the body (1).
While some mammary tumors are benign, any abnormality or change to the mammary glands should be evaluated by a veterinarian. Early detection and treatment provide the best prognosis.
Other Causes
Besides pregnancy, there are some other potential causes that could lead to nipple enlargement in female dogs:
Pseudopregnancy – Also known as false pregnancy, this is a condition where female dogs exhibit pregnancy symptoms like enlarged nipples even though they are not actually pregnant. It is caused by hormonal changes after heat cycles and usually resolves on its own after 2-3 weeks.[1]
Mammary gland hyperplasia – This is a non-cancerous overgrowth of mammary tissue that can occur during heat cycles or due to hormonal imbalances. It leads to swollen and enlarged nipples.[2]
Mastitis – This is an infection of the mammary glands usually caused by bacteria. It results in inflamed, enlarged, and painful nipples with abnormal discharge.[2]
Mammary tumors – Both cancerous and benign mammary tumors can also lead to swollen nipples in female dogs.
Other less common causes include trauma, allergic reactions, blocked milk ducts, and abscesses.
When to See the Vet
It’s important to have any significant nipple changes checked by a vet, even if your dog is not spayed and you think it may be a normal heat cycle effect. According to PawSafe.com, you should take your dog to the vet if her nipples are enlarged after a heat cycle and:
- The swelling lasts longer than 3 weeks
- The nipples feel warm, painful, or oozing
- Your dog seems sick or is acting lethargic
- Your dog’s nipples haven’t gone down after 2 months
Seeing the vet promptly can help diagnose and treat conditions like mastitis, tumors, pseudo-pregnancy, or other illnesses causing the changes. Even if it ends up being a false alarm, it’s better to err on the side of caution when it comes to significant nipple enlargement in dogs. Let your vet examine your dog and determine if any testing or treatment is needed.
Treatment
If a non-pregnant dog has enlarged nipples, the vet will first determine the underlying cause. Treatment will depend on the diagnosis.
For mastitis, aggressive antibiotic therapy is typically recommended along with warm compresses applied to the affected nipple to promote drainage and healing. The infected mammary gland may need to be surgically drained. Pain medications like NSAIDs are often prescribed as well. The dog will need to wear an Elizabethan collar to prevent licking and biting at the inflamed nipple. Severe or recurrent cases of mastitis may warrant surgical removal of the affected mammary gland(s).
For mammary gland hyperplasia, the treatment is surgical removal of the abnormal mammary tissue. This eliminates the risk of infection or future tumor development. If the condition is mild, the vet may recommend just monitoring it closely.
If the enlarged nipples are caused by a mammary tumor, treatment will depend on the type, size, location and staging of the tumor. Surgical removal is common, and may be followed by chemotherapy or anti-estrogen therapy. Benign masses can simply be monitored if small.
Regardless of the cause, keeping the dog’s mammary glands clean and dry can help prevent secondary infections. Gentle warm compresses may help reduce swelling and discomfort until the underlying cause is resolved.
Conclusion
In summary, while there are several possible causes for enlarged or swollen nipples in a female dog that is not pregnant, the most common is a false pregnancy. This happens when hormonal changes fool the dog’s body into thinking she is pregnant after her heat cycle ends. Other potential causes include mammary gland disorders like hyperplasia or mastitis, trauma to the nipple area, or mammary tumors. If the nipple enlargement is accompanied by other symptoms like lethargy, lack of appetite, or nipple discharge, it’s a good idea to visit the vet for an examination. They can help determine the underlying cause and recommend appropriate treatment if needed. In most cases of false pregnancy, the dog’s enlarged nipples will return to normal size after a few weeks. Keep an eye on any changes and comfort your pooch until her hormone levels stabilize. With the proper care and vet monitoring, dogs with enlarged nipples can make a full recovery.
