In ponyplay, one can collect semen from a male pony in three main ways:
Phantom mare, also called an artificial mare, is essentially an artificial vagina which the male pony is required to hump until he ejaculates. There are few different designs, but all perform the same basic function with the pony's semen being collected at the bottom of the tube. Optional: you can have your pony test the semen himself by making him taste it! Or you could strap the tube from the phantom mare directly into his mouth.
Electroejaculation, or transrectal electroejaculation (TREE), is performed by inserting a probe up the pony's rectum until near the prostate and applying an electric current. Optional: you can attach electrodes to his penis as well (assuming he has been a good boy) and he should have a powerful orgasm
Prostate Milking might be necessary if the pony's owner/trainer/vet needs a sample of his seminal fluid but does not wish him to achieve orgasm.