Are you referring to the hole in the hoof wall, on the right side? No, that's not an abscess, it's just a part that's missing. I would bet it developed because of lack of hoof care, though. Like others have said, he needs a farrier to work on his feet like yesterday.
As others have said, can't see anything in that unclear pic that says 'abscess' and if he's not lame, I wonder what would make you suspect it anyway?
As others have said, he is long overdue for some good hoof care. For your info - & your horse's benefit, you need to know that it's important to get a farrier to attend to their feet regularly & 4-8 weeks is the average schedule that horses need trimming. I advise you learn more about hoofcare & management. Also diet is hugely important for health & ponies especially may need to be managed carefully in this regard & not left on good pasture. Horses also generally need a dentist approximately yearly to 'float' their teeth, as they keep growing & can become sharp & imbalanced. If you need any other info on care & management of horses, just ask. There are no such thing as stupid questions, it's only the ones that are unasked & lead to neglect through ignorance that fit that bill I reckon.