Puppies and dogs don't have periods, or menstruate, the way women do. However, they do have heat, or estrous, cycles. Generally, a smaller breed dog will experience her first heat at a younger age than large or giant breed dogs. The average age of sexual maturity in dogs is between 9 and 12 months.
People think of puberty and conjure up acne and cracking voices, but your little pup doesn't show her maturity quite so clearly. When Dixie reaches puberty, she'll experience her first estrous cycle and go into heat. If she's like most dogs, she'll go into heat twice a year, though that's not a hard and fast rule. Some dogs may experience three cycles during a year, while other dogs may go 12 or 18 months between cycles. It can take a couple of years for her cycle to become established.
On average, a dog's heat cycle will last two to three weeks, though it can be quicker or longer, depending on the dog. The first sign your girl's in heat is the swelling of her external vulva, but that's not always obvious. Often, people notice that the dog's experiencing her "period," or a bloody discharge, usually a few days after the actual cycle has begun. The discharge varies according to the dog -- some dogs have very light amounts of bleeding while others experience heavy bleeding. If Dixie's a girl with a long, dark coat, you may not see any sign of bleeding. This is the first part of her estrous cycle, proestrus.
The discharge will change in appearance during the course of the heat cycle. In the beginning it will be more intense in color. As she progresses through her cycle, it will change to a pinkish, watery discharge, about seven to 10 days into her cycle. This is the point where she begins to ovulate and is most fertile -- as well as being the most receptive to mating. She's in the estrus phase of her estrous cycle.
Whether Dixie successfully mates or not, she'll enter a phase in her cycle known as diestrus, which averages about 60 days. If she's pregnant, her pups will develop and she'll eventually give birth. If she's not pregnant, she may enter a false pregnancy because her body acts like it's pregnant. She may be very motherly towards other animals or toys and she won't be interested in entertaining gentleman callers. After this phase, she'll go through the final stage of the estrous cycle, anestrus, which is a resting phase. She'll stay in anestrus until she goes into heat again.
Unless you're planning to breed Dixie, consider spaying her so she doesn't present you with a surprise -- or several of them. According to VCA Animal Hospitals, most vets recommend spaying a puppy before she's 7 months old. They note there is no behavioral benefit to allowing a dog to have a litter of puppies -- it won't make her a better companion or more social and it contributes to animal overpopulation. As well, you'll have many gentleman callers loitering about your house when she's in season.
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