I rode him very lightly with long walks and short trot laps. By the time we were done the swelling had gone down some, but was still there.
I talked to some friends at the barn and they said that the same thing was going on with their horses. And that they had heard that it was due to the "new" hay.
The horses have round bales out in the pastures but recently got new bales (not new hay but a new bale) after 2 days without having hay in the pastures.
What are your thoughts? What could be causing the swelling?