Pet careers were introduced with The Sims 2: Pets. These careers are specially employed by pets only. Sims can find jobs for their pets by reading the newspaper or looking on the computer. Pets can get promotions in a career by learning the required commands. Each promotion unlocks a fur color or collar to use in-game. Kittens and puppies cannot get jobs, and elder pets can only continue the career they have held since adult, and cannot find another job. Once an adult pet becomes an elder, the Sim can let them retire. If pets are in bad mood, they will not go to work.
Cats are paid more than dogs in all three of the pet careers. According to the Prima official game guide, it is because cats learn behaviors and commands harder than dogs, making them worth more than dogs. This is also true when selling a cat and a dog with the same learned behaviors and commands.