Excessive iron in their drinking water can be a culprit. I had mine drinking out of a dug well when I had the most trouble. I have since hooked up the barn hydrant to a cistern, which gives them rainwater. I had the water tested, and the cistern water is superior on just about every count to the well water. Linsey says nitrates inhibit thyroid activity.
Retained placenta is a common cause of laminitis.
This is a prescription drug available through vets, and has been mainly marketed for cattle. The connection between lactic acid build-up, DMG and laminitis warrants more investigation. However, this is not a substitute for mechanically restoring full hoof mechanism with a correct trim and enough movement. The letter below mentions the 4-point trim not working alone, but I have no idea if it really was an optimum trim. Further, people on the naturalhorsetrim list have been reporting getting harder hooves and faster hoof growth after adding MSM to their horses' diets.