We've only had one horse in the past who had been mistreated pretty bad as well, and wouldn't let us touch him either. The way we finally got through to him, was at feeding time. We fed him in a bucket in the pasture. We would take his food to him, and before putting it down rub him on the face...
The OP is just going to have to build up trust by handing a little every day. Everything you do with a horse, regardless of how much or how often is a training session. It's going to take some time and patience it sounds like.
It depends on how the horse progresses as an individual, and the trainers method as well. They tend to be different. One of our two Belgian draft horses was 14 when we got him, never saddled in his life. Once he understood how to lunge, and was responding on the lunge line, and accepted the...
I agree with dainerra, and I wouldn't do that either. That's going to result in nutritional deficiancies. If you feed a real raw diet, it has no sugar. Fed in variety a raw diet supplies all you need. meat/bone/organ. Everything is there, with maybe the exception of fish oil for omegas. JUst...
I pre package mine for several weeks worth at a time. Some that I buy is already packaged in the right sized amounts, so I don't even have to fool with those.
Why not just look into a raw diet? That way, you need no supplements, including the egg shells. Calcium comes from bone.(as well as other much needed nutrients in the form of minerals). In raw form, and if you feed a variety of proteins, then meat/bones/organs supply all a dog needs...
I personally have always prefered geldings. They tend to stay more even temperd, where mares go through their cycles and can become moody and have some bad attitudes. Not all are that way, but the majority are.