Laminitis in racehorses is quite common partly because the horses are fed high grain, low roughage diets. (There are other causes of laminitis, but in racehorses this seems to be one of the most important ones.) What happens is that the pH in the hindgut (the part of his digestive system where fermentation occurs) becomes very acidic. This kills the microorganisms that are found there and as they die, endotoxins are released which trigger the laminitis. Research seems to be showing that some Thoroughbred families seem to be more prone to laminitis, so genetics might seem to play a role too. The ingestion of sugars found in lush green pastures (called fructans) also play a role in laminitis.
Yes, cut the concentrates completely and offer the horse as much roughage (hays) as he will eat. The advice Kristene has given on the hay mix is perfect! You can also try good quality Eragrostis hays (Eragrostis curvula or Eragrostis teff). Sugar beet is fantastic because it is a low sugar, high caloric roughage source. It is a great source of calcium and not as high in calcium as lucerne with its associated problems. Vegetable Oils can be added to the beet pulp with great success to increase the calories in the diet without increasing the starch levels. A probiotic supplement is vital to support the microorganisms in the hindgut and to maintain the correct pH levels. It is essential in the laminitic case. It will also increase feed utilisation, thereby maintaining your horse's weight if he tends to lose condition easily.
Another way to keep your horse more comfortable is to consider stabling him on a bed of riversand. This relieves pressure on his hooves and will make him considerably more comfortable than shavings or being out on hard ground. Be very careful of working the horse on hard ground during his recovery, as it plays a role in the prediposing factors too.
Farriery relating to the laminitis case is very specialised. there are diffeerent schools of thought regarding this. Talk to as many farriers and vets as you can to get as much information as possible. Barefoot is definitely an option - especially in the acute stages of the disease. Some good results have been seen with pads (we are talking thick polystyrene type pads) and lifting heels etc, but this remains a specialty field and advice should be taken.