In the Great Famine of late 22nd Century (Gregorian calendar), traditional food sources became extremely scarce. During these desperate times, many starving humans were forced to sustain themselves on low calorie diets of domesticated animals. This led to the near-extinction of most dogs, cats and small rodents (though the Chihuahua breed of dog did became extinct for unrelated reasons).
In 2251 (Robot calendar), the Council for a New Tomorrow passed legislation that enabled the manufacture of replacements for these pets, called pet-bots. While not living animals, pet-bots are programmed to emulate the creatures upon which they are modeled. In order to have the appearance of an animal sentience, a random personality processor is built into most pet-bots.
Due to the popularity of pet-bots, it is not known if or when actual canines or felines will ever be re-introduced into conventional life.