Animal bios that are used to populate kennel cards, your website's adoptable animals page, and aggregators (Petfinder and Adopt a Pet) can be added as a Kennel Card / Website memo on an animal's record.
This is a field that can be found on intake forms (unless it is configured to be hidden) and also on an animal record's Memos tab.
If there are multiple Kennel Card / Web Site memos on an animal's record, only the most recent one will be used.