Picture belongs to NolyCS

As the mares of Ponyville goes into heat, they either have to find a stallion, or wait it out. Unfortunately, Applejack and Rainbow Dash decide to wait it out, but out of all the mares, theirs is the worst. After not being able to take any more, the two go to see Twilight Sparkle to see if she knows any spells that can rid them of their heat. Twilight doesn't know a spell, but gives them a book with a potion that can help them.

Rainbow drinks the potion, but it turns out that it changes her, while it wouldn't be so bad, her new body becomes aroused at the site of Applejack, and now she has two choices. Help Applejack, or get out.

I am in the Popular Story section, yay.

Contains: Mare to Stallion, and consensual sex.