The female dog heat cycle signals when a dog is ready to become pregnant. How frequently the cycles occur and how early depends on many factors. If you want to prevent your dog from becoming pregnant, you need to stop the heat cycle.
How Do Heat Cycles Work in Dogs
A heat cycle -- also known as estrus cycle -- refers to the period in which a female dog is fertile and can become pregnant. Dogs usually have two heat cycles a year, although this can vary among breeds and individual dogs with some dogs having cycles only once a year or less. The first heat cycle can happen anywhere between 6 and 24 months of age, also depending on each dog. The most obvious sign of estrus is vaginal bleeding, although dogs also experience swelling of the external vulva.
Medications to Temporarily Stop the Heat Cycle
If you are not ready to sterilize your dog, there are drugs a veterinarian can prescribe to suppress a dog's heat cycle. These drugs are known as Gonadotropin-Releasing Hormone or GnRH and are available as subcutaneous implants or injections. Although highly effective, the drug does have side effects, including mammary enlargement, changes in personality and weight gain.
Stopping the Heat Cycle Permanently
If a dog is not intended to be used for breeding, she should be spayed before her first heat cycle to prevent heat cycles altogether. Because it's hard to predict when the first cycle will be -- and to avoid accidental pregnancies -- it's best to spay a dog by the time she's 6 months of age. Spaying also provides some health benefits. For example, dogs who have been spayed have a lower risk of developing mammary tumors. Spaying removes the uterus so spayed dogs can't develop pyometra, a rather common and life-threatening infection of the uterus.
Benefits of Stopping Heat Cycles
Aside from helping prevent pyometra, stopping the heat cycle has other benefits. For example, spayed dogs have lower risk of developing cervical and mammary tumors. They also are less likely to develop perineal fistulas, which are common during delivery.