It Takes Two to Tango!

Do geldings ever mount mares? Yes, particularly if the mare is receptive and there's a strong emotional attachment. This type of behavior is actually not that uncommon, especially for stallions who were gelded a bit later in life and/or who had the previous experience of breeding mares prior to being gelded. Shiloh is an 8 year old mustang who was rounded up and gelded at approximately age 5. This video footage shows the first time Shiloh attempted to mount his favorite domesticated mare, Tempo (who had never been mounted, before). They are both willing partners and consenting adults who had been flirting for months. That said, and as you can see, Tempo was having a hard time understanding what Shiloh was attempting to do. It was a frustrating situation for both of them initially, but together they did eventually figure it out, and after that things became much less animated.
This is all perfectly natural behavior for horses. I'm posting this video for educational purposes because many horse owners are either not aware that geldings can/do mount mares, or believe it is inappropriate behavior that should be punished or feel the horses should be separated. Not necessarily! Male horses are hard-wired to become aroused by mares in season and even fully castrated geldings can still have a fair amount of testosterone in their systems. As long as flirting/mating behavior is not dangerous to either horse, it can be an excellent outlet for physical, emotional and relational expression.
NOTE: No baby horses will be created when these two horses mate because Shiloh is a gelding, not a stallion.