What is the ruling when an animal found to have a defect preventing its validity for sacrifice is designated for sacrifice?

Primary text

If a person designates a defective animal whose defect prevents its validity for the legally prescribed sacrifice (*ijza'*), he is obliged to slaughter it because the designation is like a vow (*nadhr*) to slaughter, which must be fulfilled. This slaughter, however, does not fulfill the legal obligation of the *Udhiyah* (prescribed sacrifice) because the animal does not meet the required standard, as indicated by the report concerning the four types of invalid sacrifices. He will be rewarded for the charity aspect of the slaughter, but he is not obligated to provide a replacement sacrifice because the *Udhiyah* was not originally mandatory upon him, nor did he perform an act that subsequently obligated it, unless the sacrifice was already an existing obligation upon him (e.g., a prior vow or replacement for a destroyed designated animal).