The Shih Tzu is a Chinese dog believed to be descended from the crossing of a Pekingese and a Lhasa Apso or Tibetan mountain dog. It is a small dog with long and dense hair. The breed's lively, friendly and loyal personality has contributed to their popularity as house pets. According to the American Kennel Club registration statistics, the Shih Tzu was the 10th most popular dog breed in the United States in 2010.
A female dog goes through numerous reproductive cycles -- called the estrous cycle -- throughout its lifetime. When a female dog is going through its estrous cycle, it is commonly referred to as being "in heat." A Shih Tzu's first cycle can come anytime from 6 to 15 months of age. A female that has not had its first cycle after 15 months of age should be checked by a veterinarian. It will go through a cycle, which lasts for two to four weeks, about every seven months.
When a Shih Tzu dog is in heat, its temperature rises and there will be a red or pink colored discharge from her swollen vulva. Other signs of being in heat include fatigue, restlessness, increased urination and mood changes. Since the Shih Tzu is ready to mate, it will obviously attract more interest from male dogs and in turn be more attentive to them.
While a female Shih Tzu goes through estrous cycles, a male Shih Tzu is ready to mate any time after it reaches sexual maturity. A large dog breed can take as long as 18 months to reach sexual maturity; but a Shih Tzu reaches sexual maturity around 8 to 9 months of age. A male Shih Tzu can smell a female dog in heat from as far away as three miles and may become very aggressive in trying to reach and mate with her.
A female Shih Tzu will be receptive to a male's advances when it wants to mate. Signs that point to it being pregnant are behavioral changes, swelling of the vulva without bleeding, increased nipple size and a swollen stomach. The gestational period lasts between 56 to 63 days. A typical litter size is four puppies. Veterinarians recommend spaying the Shih Tzu, once it has been bred -- as it will continue to go through its estrous cycles until the end of its life -- which puts more stress on the body, if not spayed.