Leviticus 27:9-13

9If he vows an animal that may be brought as an offering to the LORD, any such animal given to the LORD shall be holy. 10He must not replace it or exchange it, either good for bad or bad for good. But if he does substitute one animal for another, both that animal and its substitute will be holy.

11But if the vow involves any of the unclean animals that may not be brought as an offering to the LORD, the animal must be presented before the priest. 12The priest shall set its value, whether high or low; as the priest values it, the price will be set. 13If, however, the owner decides to redeem the animal, he must add a fifth to its value.