Have you had your hay analyzed, for sugar,starch and especially for nitrates? EquiAnalytical does hay analysis. I have two mini's, one of them having been diagnosed in 2011 as insulin resistant. Since then I had both on a low sugar/low starch diet of orchard or timothy hay, depending on availability, and timothy pellets, and they were doing great until last year when my mare became laminitic.
Long story short, after much struggle, MANY vets bills, and so much pain on my mares part, we were able to track down high nitrates in their hay. I had only been having a regular analysis done, which does NOT include nitrates, so we were unaware of how high the nitrates actually were, which turned out to be 2200 PPM, which is toxic. This is toxic to any animal and can kill a cow. Horses are much less sensitive to nitrates than cows or goats, so my minis were able to tolerate it, but with consequences that I then had to deal with. I can't tell you how stupid I felt when I got that analysis result back.
I read that nitrates fluctuate in the hay, depending on the weather when it is cut, whether it is irrigated, what it is fertilized with; so many variables. My timothy and orchard hays had been coming from the western part of the US and I was told that the severe weather they have been having the past few years had affected the hay crops. I now feed coastal grass hay and test every new load for nitrates before feeding it. You can soak it in water to reduce nitrates, but that is very difficult in winter weather for many people.
Anyway, if the blood tests for insulin resistance have not been done ( glucose, insulin and leptin ) I would consider having them done. It's much less expensive and easier than dealing with a colic. Also make sure that the blood samples are handled correctly in order to get accurate results; I'm pretty sure they need to be frozen and shipped on ice. I think Cornell U is the only place to get a leptin run.
Sorry this has been so long, but if I can help keep someone from going through what my mare had to go through, it is a good thing. She's much better now, but it's been a long six months journey. Good luck with your boy. He's beautiful!