I disagree, the reason being that humans do not tolerate such nonsense.
Heroes would rise, speeches would be made, epic battles would follow, and the enslaved humans would triumph in most awesome fashion, eventually.
Pets, however...
Well, it's hard to be mad about being a pet. You want to be upset, but there's yummy food and a cozy bed and head-rubbies and no one expects anything from you, you don't have to work, and your responsibilities number: 1. Cheer master up when you can and 2. Indulge all creature comforts.
In summation: Human slaves result in chain-breaking and big battles. Human pets? We'd strap the collars on ourselves.