hey, well last summer my horse went lame for 8 weeks due to stone bruises, he has been barefoot all of his life and for the first time last summer we had to put shoes on him. We figured that it was the on and off rain, just like what you described. If he doesnt get any better in a few weeks I would reccomend putting shoes on him.. that is what worked for my boy :)
~He knows when you're happy
He knows when you're comfortable
He knows when you're confident
And he always knows when you have carrots.