As Smarts were to uplifts, Zeroes were to bouncers. While Smarts were bred for intelligence, Zeroes were bred for health in zero and micro gravity environments. Zeroes were some of the first animals bred/engineered for off-Earth environments, as well as some of the first testbeds for early medichines.
Zeroes were at first broad mixes of dog breeds, combined for maximum diversity. All Zeroes were inoculated with medichines, providing a constant stream of information on the health of their hosts. They were prone to the usual health problems that come with zero/micro-gravity, but were kept healthy by the intervention of their medichines. The less medichine intervention any dog required, the larger their genetic contribution to the next generation. In this way, the dogs were slowly adapted to zero gravity, minute medichine-sourced records of their development were made, and the dogs maintained excellent health.
The descendants of Zeroes can still be found as pets throughout the system, popular mostly among wealthy Lunar citizens in micro-gravity habs. The unusual flexibility and dexterity of the breed makes them keen competitors in agility competitions.