A simple level/upgrade system for pets such as wolves and cats

Pets are something everybody loves in minecraft, but unfortunately they're often a burden to carry with you on adventures. That, and they feel more like disposable soldiers. What if there's a simple leveling system similar to villager badges (stone > iron > gold > emerald > diamond), but on their collars? As you spend time with them, they'll eventually grow, increasing its health and damage by a little bit per rank. This'll create more attachment with said pet.