ITA with walkinthewalk. Hoof health is more than just biotin (which is just a B vitamin); copper, zinc, iron, etc. are all important to hoof quality as well. The first thing you should look at when you have a problem like poor hoof quality is whether or not you have a solid nutrition plan in place. Mane 10
doesn't look like a particularly high quality feed. They don't list the NSC (starch & sugar content) but with corn as the 2nd ingredient you can bet it's very high. The oats and molasses don't help either. It also seems very low in the vitamins it lists. For example, it has 4,000 IU per lb of Vitamin A. For my horse, a ~1050 lb 15hh gelding in light to moderate work, the daily recommended intake of Vit A is ~32,000 IU. So, to get enough Vit A, he'd have to eat 8 lbs of Mane 10. I don't know about your horse, but mine would get pretty pudgy from 8 lbs of feed a day. And vitamin A is important- deficiencies leave horses much more prone to fungal infections like rain rot, among other things. Not to mention that even with 8 lbs, my horse would still fall just shy of the RDI for copper.
Not sure what the other pelleted feed you're mixing it with, but there really shouldn't be any need to mix feeds unless you're transitioning from one to the other. FeedXL.com
is a great online resource for determining your horse's nutritional needs. You can enter in the amounts and which brands of feed you're using (it has most feeds already in their database; if you happen to run into one they don't already have, they'll add it for you) and it will show you how that diet is doing as far as fulfilling nutritional requirements.
If you're interested, the people on this forum could probably help you figure out a diet that's good for your horse- though we won't be able to give you as detailed an analysis as FeedXL.