A female dog bleeding from her vulva is either going through her normal heat cycle or showing signs of a medical problem that needs veterinary attention. The most common cause in unspayed dogs is the proestrus stage of heat, which produces bloody vaginal discharge lasting six to eleven days on average. But if your dog is spayed, past breeding age, showing other symptoms like lethargy or excessive thirst, or the discharge looks unusual, something else is going on.
The Heat Cycle: The Most Common Cause
If your dog hasn’t been spayed, the most likely explanation is that she’s in heat. The canine reproductive cycle has four stages, and bleeding happens during the first one, called proestrus. During this phase, the ovaries produce estrogen, which causes bloody vaginal discharge and visible swelling of the vulva. This stage lasts roughly six to eleven days. You’ll also notice male dogs showing intense interest in her, though she won’t be receptive to mating yet during this phase.
Most dogs go into heat for the first time between six and twelve months of age, though larger breeds can start later. Cycles typically repeat every six to eight months. The blood is usually bright red at first, then gradually lightens to a pinkish or straw-colored discharge as she moves into the next stage. If you know your dog is unspayed and the timing lines up with her normal cycle, this is likely what you’re seeing. The bleeding should stop on its own within about two weeks.
Uterine Infection (Pyometra)
Pyometra is a serious, potentially life-threatening infection of the uterus that most commonly develops in unspayed middle-aged and older dogs, usually within a few weeks after a heat cycle. There are two forms. In “open” pyometra, the cervix stays open and the infection drains out, so you’ll see vaginal discharge ranging from pus-like and yellowish to bloody. In “closed” pyometra, nothing drains, the abdomen may swell visibly, and the dog becomes much sicker because the infected material is trapped inside. Dogs with closed pyometra face a higher risk of sepsis.
Beyond the discharge, watch for increased thirst, decreased appetite, vomiting, lethargy, and fever. Pyometra requires urgent veterinary treatment, almost always surgery to remove the infected uterus. Left untreated, it can be fatal within days.
Urinary Tract Infections and Bladder Stones
Sometimes what looks like vaginal bleeding is actually blood in the urine. Urinary tract infections are common in female dogs and cause blood-tinged urine, straining to urinate, frequent small urinations, accidents in the house, foul-smelling urine, and excessive licking of the genital area. You might notice pink or red spots where your dog has been lying or small drops of bloody fluid when she squats to pee.
Bladder stones can cause similar symptoms. Mineral deposits form in the bladder and physically irritate its lining, producing visible blood in the urine along with straining and discomfort. Your vet can distinguish between vaginal bleeding and urinary bleeding with a urine sample and often an ultrasound. Both conditions are treatable, but bladder stones sometimes require surgical removal if they’re too large to dissolve with a dietary change.
Tumors and Growths
Transmissible venereal tumors are a concern in dogs that have had contact with strays or unfamiliar dogs. These growths typically appear on or around the genitalia, starting as small reddish bumps that can grow into large, cauliflower-like masses up to 15 centimeters across. They bleed easily and often produce a foul-smelling, blood-tinged discharge, especially if they become secondarily infected. These tumors spread through direct contact during mating, sniffing, or licking of an affected dog’s genitalia.
Other types of vaginal or vulvar tumors can also develop, particularly in older dogs. Any visible mass, persistent bloody discharge, or foul odor warrants a veterinary exam. The good news is that transmissible venereal tumors respond well to treatment, and many other reproductive tumors in dogs are benign.
Rodenticide Poisoning
If your dog has access to garages, sheds, barns, or areas where rat poison might be stored, this is a cause worth knowing about. Anticoagulant rodenticides, the most common type of rat and mouse poison, work by preventing blood from clotting. A dog that ingests even a small amount can develop internal bleeding that shows up as vaginal hemorrhage, bloody urine, nosebleeds, bruising, or blood in the stool. In one documented case, an otherwise healthy dog presented with significant vaginal bleeding as the only sign of rodenticide poisoning, with the uterus found full of coagulated blood. If there’s any chance your dog got into rat poison, this is an emergency.
Bleeding in Spayed Dogs
If your dog has been spayed and you’re seeing vaginal bleeding, that narrows the possibilities and makes a vet visit more urgent. Spayed dogs don’t go through heat cycles, so the bleeding is coming from somewhere it shouldn’t be.
One possibility is ovarian remnant syndrome, where a small piece of ovarian tissue was left behind during the spay surgery. That tissue can still produce hormones and cause heat-like symptoms, including bloody discharge. Another is stump pyometra, where the small remaining portion of uterine tissue left after spaying develops an infection. Urinary tract infections, bladder stones, vaginal tumors, trauma, and clotting disorders are all possibilities in spayed dogs as well. Rarely, a foreign body lodged in the vaginal canal can cause chronic bloody or pus-like discharge. In one case, a retained fragment from a previous pregnancy was discovered years later as the source of ongoing vaginal discharge in a spayed bulldog.
What Your Vet Will Do
Your vet will start by figuring out where the blood is coming from: the vagina, the uterus, or the urinary tract. This typically involves a physical exam of the external genitalia, looking for evidence of blood, trauma, or visible growths. A vaginal swab can help determine whether your dog is in heat or dealing with an infection. The appearance of the vaginal lining itself gives useful clues about the stage of the cycle or the presence of inflammation.
Beyond the physical exam, expect a urinalysis to check for infection or blood in the urine, and possibly an abdominal ultrasound to look at the uterus, bladder, and kidneys. If a clotting disorder is suspected, blood work will check how well your dog’s blood is coagulating. Cultures from vaginal swabs can identify specific bacteria if infection is involved.
Signs That This Is Urgent
Some causes of vaginal bleeding can wait for a regular vet appointment. Others can’t. Seek same-day or emergency veterinary care if your dog is showing any of these alongside the bleeding:
- Lethargy or weakness: she seems unusually tired, reluctant to move, or unsteady
- Pale gums: lift her lip and check; gums should be pink, not white or grayish
- Swollen abdomen: especially in an unspayed dog, this could indicate closed pyometra
- Excessive thirst and urination: a hallmark of uterine infection
- Heavy or continuous bleeding: more than light spotting that soaks bedding or leaves large puddles
- Vomiting, refusal to eat, or fever: signs of systemic illness
- Known or possible exposure to rat poison: treat this as an emergency regardless of other symptoms
A young, unspayed dog with mild spotting and a swollen vulva who is otherwise acting normal is most likely in heat. A spayed dog with bloody discharge, an older dog with foul-smelling drainage, or any dog bleeding heavily with changes in behavior needs prompt professional evaluation.