Why Is My Female Dog’S Back End Swollen?

A swollen back end in female dogs is a common issue that dog owners may encounter. The medical term for this condition is peri-vulvar edema. There are several potential causes for this swelling, which can range from mild to quite serious. Some of the main reasons a female dog’s back end may become swollen include:

  • Heat and estrus
  • Pregnancy
  • Pyometra (uterine infection)
  • Abscess
  • Hernia
  • Trauma
  • Allergies
  • Tumors

Determining the specific cause of swelling requires an examination by a veterinarian. Some causes like pregnancy or estrus are normal, while others like pyometra can become life-threatening if left untreated. This article will provide an overview of the various reasons a female dog’s rear may become swollen and explain when veterinary care should be sought.

Heat and Estrus

Heat cycles, also known as estrus cycles, are a normal part of a female dog’s reproductive system. An estrus cycle lasts around 18-21 days and occurs roughly every 6 months once a dog reaches sexual maturity, which is usually between 6-24 months of age.

During the estrus phase, which lasts around 9 days, the dog’s ovaries release eggs and the hormones estrogen and progesterone increase in the bloodstream. These hormonal changes cause the vulva to swell as blood flow increases to the area. The vulva will become enlarged, reddened and protrude slightly. This swelling allows easier access for mating.

Other signs of estrus include bloody vaginal discharge, increased urination, nervous/agitated behavior and receptiveness to male dogs. The discharge starts off bloody and then becomes lighter in color and watery. Swollen vulvas and vaginal discharge are some of the most obvious physical indicators that a dog is in heat (WebMD).

It’s important to note that the swelling of the vulva occurs whether or not the dog is bred during her heat cycle. The swelling begins early in the cycle and persists through the full 9 days of estrus as hormones elevate in preparation for mating and ovulation.


Pregnancy can commonly cause swelling of the genital area in female dogs. As the puppies develop and the pregnant dog’s belly swells, this puts pressure on the blood vessels and lymph nodes around the rear end and vulva (external genitalia). The pressure slows blood return from the rear limbs and genital region, causing fluid accumulation and swelling (1).

Additionally, the pregnant dog’s body produces increased levels of the hormones estrogen and progesterone. These hormones cause the vulva to enlarge and swell in preparation for birth. The swelling is especially noticeable during the last 2-3 weeks of pregnancy as the hormones peak. The nipples may also enlarge. These are normal changes, as long as the swelling is not severe (2).

Excessive swelling of the abdomen during pregnancy can signal a dangerous condition called canine maternal hydrops. This is an abnormal buildup of amniotic fluid that puts pressure on the mother’s organs. Signs include swelling extending up the sides, breathing difficulty, lethargy, and vomiting. This requires prompt veterinary treatment (3).

Most swelling during a normal pregnancy will resolve after the puppies are born. If the new mother dog seems uncomfortable or the swelling persists longer than a week post-whelping, a vet visit is recommended.


Pyometra is an infection of the uterus that causes swelling of the female dog’s back end. It occurs when bacteria enter the uterus and cause inflammation and pus accumulation. Pyometra typically happens in middle-aged to older female dogs who have not been spayed. There are two types of pyometra:

Open pyometra occurs when the cervix is open, allowing discharge to exit the uterus. This results in symptoms like fever, lethargy, increased thirst, vomiting, and a purulent, smelly vaginal discharge (The vets). Closed pyometra occurs when the cervix closes, trapping infection inside the uterus. Dogs with closed pyometra may show symptoms of illness but no vaginal discharge (Wagwalking).

Both open and closed pyometra can cause dangerous toxins to enter the bloodstream. Swelling of the uterus stretches the abdomen, causing discomfort. Without treatment, pyometra can be fatal. So it is crucial to get veterinary care if pyometra is suspected.


One of the most common causes of swelling near a female dog’s anus are abscesses in the anal glands1. Anal glands are small sacs located on either side of a dog’s anus that fill with fluid that is normally expressed when they defecate. However, sometimes these glands can become blocked, infected or impacted, leading to an abscess forming in the gland.

Symptoms of an anal gland abscess typically include swelling, pain and redness near the anus. The area may feel warm or hot to the touch. Dogs with an abscess often scoot their rear along the floor due to the discomfort. In some cases, the abscess can rupture and drain pus or blood from the rectum.

Treatment involves draining the abscess by a veterinarian and flushing the area. Antibiotics may be prescribed to treat or prevent infection. Sometimes the vet may recommend removing the anal glands if abscesses are a recurring problem. Anal gland abscesses can be very painful and should be treated promptly by a vet.


A perineal hernia is a fairly common condition in intact (non-neutered) older male dogs where the muscles around the rectum weaken and the rectum bulges under the skin. This causes swelling around the dog’s anus and rectum, creating a hernia-like bump. Perineal hernias are usually diagnosed through a rectal exam where the vet can feel the hernia swelling. They are caused by the gradual weakening of the pelvic diaphragm muscle over time, which allows fat and internal organs to push out. This is more common in dogs that are not neutered.

Some key signs of a perineal hernia include the swelling around the anus, trouble defecating or sitting, constipation, straining, and blood in the stool. Surgery is often required to push the organs back into place and stitch up the muscle wall. Without treatment, a perineal hernia can become strangulated, cutting off blood flow. This is a life-threatening emergency requiring immediate veterinary care. Prompt surgery can allow dogs with perineal hernias to live comfortably.


[Perineal Hernia in Dogs – Digestive System](https://www.merckvetmanual.com/digestive-system/diseases-of-the-rectum-and-anus/perineal-hernia-in-dogs)

[Perineal Hernia in Dogs](https://www.embracepetinsurance.com/health/perineal-hernia)


Traumatic injuries like bites or accidents can cause swelling and bruising in a dog’s rear end or back legs. Blunt trauma from being hit by a car or falling can damage soft tissues like muscles, tendons, and ligaments (WagWalking, 2022). Signs of soft tissue trauma include:

  • Swelling, bruising, or inflammation around the injured area
  • Skin discoloration or redness
  • Lameness or difficulty walking
  • Visible wounds like gashes or punctures

Bite wounds are another common cause of rear leg swelling in dogs. Dog bites often target the hindquarters and can cause severe tissue damage. Deep puncture wounds are prone to infection which leads to inflammation and fluid buildup under the skin (PetMD, 2023).

Regardless of the cause, trauma causes leakage of fluid and blood into the surrounding tissues. This leads to swelling, bruising, and pain. Prompt veterinary care is crucial to treat wounds, drain fluid, prescribe antibiotics, and minimize lasting damage from trauma (GoodVet, 2022).


Allergies can also cause swelling and inflammation in a female dog’s rear end.[1] When a dog is exposed to an allergen, her immune system overreacts and releases histamine, which leads to itching, swelling, and irritation.[2] Common allergy symptoms in dogs include red, itchy skin, especially on the paws, belly, groin, armpits, head, face, and rear end.

Dogs can develop allergies to things like pollen, mold, dust mites, flea bites, certain foods, and more. These allergens can cause a dog to lick, bite, and scratch at her rear, leading to hair loss, hot spots, swelling, and rashes around the vulva, anus, and tail. Allergies should be treated through medications, anti-itch shampoos, and removing the allergen source if possible.

Severe or chronic allergies left untreated can cause significant inflammation and fluid buildup in a female dog’s rear. So allergies are one potential cause of swelling that should be evaluated by a veterinarian.


Tumors in the reproductive tract or mammary glands can sometimes cause swelling of the vulva/vagina area in female dogs. Tumors may be malignant (cancerous) or benign (non-cancerous).

Some types of tumors that can lead to swelling include:

  • Mammary gland tumors – Tumors in the mammary glands are common in unspayed older female dogs. They often appear as single or multiple lumps under the skin of the mammary tissue.
  • Vaginal/vulvar tumors – Either benign or malignant tumors of the vagina, vestibule or vulva itself can lead to enlargement of the genital region.
  • Ovarian or uterine tumors – Tumors affecting the ovaries or uterus internally can cause abdominal enlargement that is visible externally at the vulva.

Any abnormal swelling in an intact female dog should be evaluated by a veterinarian. Imaging tests like x-rays, ultrasound or an MRI may be recommended to diagnose tumors. Treatment depends on the type of tumor and may involve surgery, chemotherapy or radiation.

When to See the Vet

Swelling around a female dog’s rear end may signify a minor issue that can be treated at home. However, if the swelling persists, grows larger, or is accompanied by other symptoms, it’s essential to have your dog examined by a veterinarian.

Some signs that warrant a vet visit include:

  • Swelling that does not improve with warm compresses and over-the-counter pain medication
  • Sudden onset of significant swelling
  • Swelling that is accompanied by bleeding, pus, or a foul odor
  • Difficulty urinating or defecating
  • Lethargy, loss of appetite, vomiting, or other signs of illness
  • Scooting rear along the floor
  • Excessive licking or biting at the rear end

A veterinarian can perform an examination to determine the underlying cause and provide appropriate treatment. Delaying medical care with significant swelling could lead to rupture or abscess. It’s always better to seek veterinary advice to ensure your dog’s health and comfort.

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