I have a dozen or so books floating around in my head that made a huge impact on me. What Worse Place Can I Beg in Your Love by Syd McGinley is one of them.
The premise of the book is that Dave is on a spacecraft, and was recently dumped by a master who called him annoyingly obedient. Dave's ex-master replaced him with someone less submissive, and Dave is still trying to figure out where that leaves him... if he'll ever find anyone who can handle the level of submission he wants to give.
The spacecraft crash-lands on an alien planet and Dave finds himself in a jail cell. He is eventually "adopted", he realizes, in much the same way someone would go to a dog pound and adopt a dog. The species on this planet is very large (seven plus feet) and they don't speak English. Dave is not allowed to try to learn their language. He is nothing more than a pet. A pet who is eventually used for sex. It's an M/m story, so if that's not your thing then beware. But if you can deal with it, the D/s is exquisite. Dave wants to submit, and he revels in being nothing more than a pet who has no say in anything at all that happens to him.
The science fiction fantasy element worked to make the pet fantasy real... not play pretend. At the time I read it, it was the first such type of story I'd read. I now know there are similar books, some that predate this one, so it's not the first written with this idea. But this was my first and it stuck with me.
I am not a pet in our home, nor have I ever been treated like one, other than short role playing scenes. But I admit the fantasy of being treated that way for an extended period of time with no way to safeword out is a huge turn on for me. I might even agree to it for real if it were for a week or less. As long as I got to eat human food.
Books with similar themes
Anneke's Owned And Owner is an M/f story that involves a female from one planet being treated as a pet on another planet. And I loved the section in Anneke's As She's Told where Maia is treated like an animal for most of a summer. Not the same animal the entire summer, but the idea is there, where there is no language allowed. Because the people in the house are speaking Danish, which she doesn't understand, she doesn't even have the ability to know what they are saying, other than basic commands they give her. I love that Anneke found a way to make it real without the science fiction element.
Not exactly the same theme, but another series where one species basically turns another into a sexual pet is the Interstellar Service & Discipline series by Morgan Hawke. This particular species has two penises, so you get it in both holes every time you have sex. The best from this series is Victorious Star, but I also enjoyed Fallen Star.
And finally, Obedience Training by Mya gives us a four armed (huge) golem who makes a very willing pet out of a werewolf. That's another M/m one though, so beware if that doesn't do it for you.
Do you have books with this theme that you've enjoyed? One that turns the whole "pet" idea into something more than just playing around? I would love to hear about them.