How Should I Go About Gaining Trust From My Yearling Colt?

I recently rescued a paint horse from a farm where there were fourty other extremely malnourished horses. All of the horses had no human contact what so ever, and they wer all extremely timid and showed severe signs of fear (bucking, running a loud noises, snorting, ears laid back, ect.). The horse I rescued is a yearly stud. We have only been able to get a halter and short lead rope on him so far, while he was in a stall. I