What Causes a Dog to Swell When in Heat?

When a female dog comes into heat, or estrus, she is fertile and can become pregnant. During this time, her vulva will swell due to the increased production of estrogen, which also causes a discharge of blood from the vagina. A dog in heat will lick the area, located under the tail, with frequency when she is in heat. The swollen tissues make penetration easier for the male dog when he mates with her. However, vulvar swelling can occur for other reasons, so you should learn to recognize the signs of estrus versus signs of other problems.

  1. The Heat Cycle

    • According to Webvet.com, a dog comes into heat as early as 6 months and as late as 2 years old; small dogs usually start sooner than the larger breeds. The heat cycle lasts between 18 and 24 days and starts with vulvar swelling and bloody discharge, which gradually becomes clear. During this process, a dog may become pregnant, so unless you want a litter of puppies, isolate your female dog from males until the cycle is over.

    Other Causes of Vulvar Swelling

    • A dog's vulva may swell for reasons other than estrus. According to VetInfo.com, they include allergic reaction, labor complication, infection, and forced separation during mating. Never attempt to separate dogs after the mating process has begun, because the male dog's penis swells during copulation and can damage the female if forcibly removed.

      If your dog's vulva is swollen and you suspect a problem other than estrus, take her to the veterinarian immediately.

    How to Prevent Vulvar Swelling

    • Depending on the cause, you can prevent vulvar swelling in your dog. If the cause is estrus, the easiest way to prevent swelling, and pregnancy, is to have your dog spayed, preferably before she ever goes into heat. Spaying is recommended for all dogs who will not be used for breeding purposes; WebVet.com states that spaying has many health benefits, including prevention of certain types of cancer, as well as uterine infection and wandering in search of a mate.

      If your dog is not in estrus, or has been spayed, and you notice vulvar swelling, take her to the veterinarian immediately.

    The Myth of Spaying

    • A common myth is that every dog should have at least one litter of puppies. This statement is inaccurate and has historically tragic repercussions. According to the American Humane Association, every year shelters take in approximately 8 million unwanted animals, and nearly half of those must be euthanized. If you do not plan to breed your dog, you should consider spaying her to avoid unwanted pregnancies, wandering and health problems, as well as adding to the overpopulation of unwanted dogs.