This story is a Patreon commission by theian, and contains themes like public exhibitionism, public use, loss of reproductive agency (not able to choose who he impregnates), cock milking, artificial insemination, and impregnation. Also, the cover page is the cropped part of an impressive piece made by dimwitdog on Derpibooru.

Sweet Apple Acres may have been a successful business in Ponyville, but it still had a hefty amount of debt that was hard to ignore. As deadlines draw near, and options begin to run out, Applejack and Starlight Glimmer compose a rather... unconventional idea. Since Big Macintosh was a highly saught-after stallion (even with a marefriend), and had undoubtedly amazing genes, the two suggested that he should be the theme for a fund-raiser.

More specifically, his sperm.

Even though the idea of being milked as breeding stock for a public auction sounded downright insane, Big Mac understood the farm's dire finances enough to agree to the plan. He may have had no idea if his marefriend would be able to win, but would he still regret the auction by the time it was over?