I appreciate the willingness of Linden Lab to work with us on fine tuning the marketplace categories. I would say that setting up categories based on individual companies isn't the best method since companies can come and go. Neither is trying to set up groups by type of animal because you will invariably leave some animal out - or many, in this case. Right now, the listings leave out over half of the breedable pet types. There are *many* other pets besides cats, dogs, and horses.
I would suggest categories of Breedable Pets/Pets, Breedable Pets/Food and Boosters, and Breedable Pets/Accessories and Buildings. (or something similar) That way the categories are all inclusive, yet divided up enough that people can find what they are looking for quickly.