Pet records, weights, routines and the species you work with.
Animals belong to a customer, so the owner must exist first. Only the name, date of birth and species are required. Species is a dropdown fed by Settings then Animal Species — if the one you need is missing you have to add it there first, you cannot type a new one on the animal form.
An animal's record holds its details, appointment history, behaviour and general notes, custom fields and files. Edit Animal in Quick Actions changes the details; Transfer to Another Customer moves the animal and its history to a different owner. When an animal stops coming, set it to not active rather than deleting it so the history survives.
Species control what you can pick when adding a pet. Set up the ones you work with under Settings before you start adding animals, and only remove a species nothing is recorded against.
The Last Visit report under Animals sorts every animal into five bands by how long it has been since their last appointment: scheduled, recent, due soon, overdue and lapsed. Overdue is the band worth acting on — customers who used you regularly and stopped. Lapsed also contains animals that were added but never visited at all.
If you can't find the answer here, raise a ticket from inside PetDesk and it comes straight to us.