Firstly, yes, of course you're welcome to continue picking our brains - that's what we're here for! If you can send some hoof pics and the xrays, that would help us give you more specific answers.
Sounds like he's probably on a good wicket diet-wise & now being on f/t turnout.
Especially as it was a spring thing, I would suspect laminitis may have at least a part to play. Abscesses are one of the symptoms of IR type probs. I'm no kind of nutritional expert in the least & I use a fantastic service/program called feedxl.com which also has resident nutritionists & takes the headache & confusion out of balancing diets, especially for those with ailments. There are also heaps of great articles on the site relating to feeding & feedstuff. Eg. sugars in pasture - there's less in early morn, so afternoon would be more appropriate for grazing muzzles. There is also a good website safergrass.org which has a lot of info on feeding lami-prone beasties.
It is very common for domestic horses to have weak, sensitive heels. This can start a whole field of balls rolling, such as horse tippy-toeing, losing natural shock absorbtion, foundering, heels growing longer &/or underslung, frogs getting thrushy & wasting away, or prolapsing in an attempt at ground pressure.... Abscesses can be one of many symptoms of heel weakness. I believe boots &/or pads are generally the best thing for getting a horse to *comfortably* use & therefore strengthen his heels and subsequently the rest of his feet.
Anyway, just some more food for thought. Hope it helps!