From what I remember the story was a gender bender, with not a lot of chapters, was definitely mature.

Basically theeres two male roommates with one turning into a mare and then it follows those two struggling to deal with the whole pony thing, and I believe there's a race track/stable involved but not hundred percent sure.

Story found by https://www.fimfiction.net/user/78584/dferbrt

https://fimfetch.net/story/144541/call-of-the-wild#:~:text=Call%20of%20the,Rustle%20my%20Jimmies

7867605

Yup that's it thanks!

7867605
Oh man, I remember this now. This was hot. Unfortunate that it was never finished.