The advancement to be used, placed in world/data/advancements/custom/breed_relog.json
And the following commands to test it at will:
- Breed two animals together.
- Save and exit the world before they finish.
- Re-enter and allow them to finish, but you will not be awarded the advancement.
The animals do not save their breeder's UUID to NBT, unlike zombie villagers saving the curer's UUID for the minecraft:cured_zombie_villager trigger.