It seems like a good thing to do, simply get all owner information and their pets (names/ID's or so) during prerun of Mod::Owner and get the Pet information and user (name/id) during the Mod::Pet prerun but...
But, what if some crazy pet owner starts breeding then and ends up having hunderds up on hunderds... you might be fetching way to much data that in the end you never use thus making your application less scallable then you might want
I would simply fetch the owner details during Mod::Owner prerun and fetch the pets information if and when the user needs this data, using a little AJAX/Web2.0 sauce you can do this even without reloading your page. This makes your application seem faster as you only load data when needed. You could even go as far as to only fetch 100 pets at a time if you suspect that those crazy pet breeders might cause you trouble in the future
From a design perspective it makes perfect sense to fetch the data that you will be modifying but be very careful that you don't over eat on data that you do not need
