I agree with Always, that yes it is his belly button but could also be a small umbilical hernia (which occurs at the belly button). Can you push up on it and make it go away? If so it is a hernia and will need to be repaired. I assume he is a gelding but animals with umbilical hernias should not be bred as it can be passed on to their offspring.
How come so many people aren't aware of pony belly buttons? I'm not saying it to be rude, and I'm sorry if it comes across that way, but I've had a number of friends call me panicking because they finally found it. O_o Posted via Mobile Device
A lot of people don't know horses have ergots on their fetlocks either. Some people have owned horses their whole lives and never heard of an ergot. But I can see the concern over the belly button if it is an outie and you never saw it before!