Any good slave stories? [NSFW]

(Should this be tagged NSFW?)  
I’m looking for stories where ponies are forced to work as slaves (Like in ‘A dog and pony show’ for instance.) Any stories you would recommend? (Mane 6 and/or CMC preferred.)

@Gadgetphile  
My little slave. It’s 34 chapters and involves flutters. It’s on fimfiction. Make sure you have mature turned on.

Every Spike appearance in the series lol.

@Toffee  
That’s sex slave. I’m looking for working horses.