It is a time consuming process & then they have to like it.
My vet used to carry Royal Canin in her office & prescribe it.
Bailey was fed RC by her breeder so I fed her that also. Then she started to get sick a lot. My vet tested her for a few common allergies.
Corn is a biggie for her, but after that my vet switched to another brand of food to carry in her office. She said too many other animals were also having reactions.