When you offer a sacrifice to ask my blessing, there must be nothing wrong with the animal. This is true, whether the sacrifice is part of a promise or something you do voluntarily.
Bulls or rams or goats are the animals that you may burn on the altar as sacrifices to please me. You may also offer sacrifices voluntarily or because you made a promise, or because they are part of your regular religious ceremonies. The smell of the smoke from these sacrifices is pleasing to me.