If he was kept stalled, on sweets &/or otherwise grainy/starchy feed, too little roughage, and fed the 'high octane' meals only once daily, I'm not surprised he's a 'hard keeper'. Has he been checked/treated for ulcers? Hind gut acidosis? Does he get a probiotic? Extra magnesium? They are some of the measures I'd be considering strongly, along with other's good advice.
Ed to add... didn't read more than 1st page before above. I see you've had some success. Re above, I'd probably work towards reducing/removing the Nutrena & building up the alfalfa. I'd also be including whatever appropriate nutritional supps will 'fill the gaps' in that diet.
While if he gets some green pick daily, his biotin levels aren't likely to be low, studies have shown that hoof growth speeds up (not nec strength or health) with high levels of biotin, even in excess of dietary requirements, and it's safe to do so. But that is but one of many 'ingredients' needed for healthy hooves, coat, skin, etc that are likely lacking/imbalanced in the diet. I'd look at providing all he needs rather than just one ingredient.
Also crappy feet may have more to do with diet than nutrition as such, &/or environment & management too.
Last edited by loosie; 11-12-2013 at 12:48 AM.