The higher the breeding power, the more the creature will breed. Breeding power depends on NPC race and level. Those listed are at the level the NPC is spawned at. Not all NPCs are obtainable as pets. The more creatures there are already on a ranch, the less a chance for the next one to breed. Breed power formula: BP = RaceBreedPower * 100 / (100 + [Level * 5]) For example, rabbit race has breeding power of 800, so level 1 rabbit will have 800 * 100 / 105 = 761 breed power.