Bad behavior in Colt

I have a mare who was approx. 60 days overdue when she had a healthy well developed colt. The mare harshly rejected the colt at first and would not let him nurse without human intervention but is now allowing him to nurse. The problem is he is an absolute terror. The mare has given up on any and all disciple actions and lets the colt (now 10 days old with very sharp teeth) bite and kick her without even the slightest reaction on her part. The colt who was friendly to humans has become a target for his aggressive biting and kicking. When leading mare to arena for exercise the colt does not stay by her side but RUNS out of site or a good 300+ feet in every direction. Needless to say, I realize the hazards to the colt, mare and any humans is a real issue here, but handling him is turning into a real battle. My mare is just about the most fearless, respectful mare I have ever seen. She trusts humans without question and would almost gladly let me take the colt off to wherever without even a slight nicker...Any solutions or advice would be so helpful. Like I said it has only been 10 days since he was born, and acts like a mature stud horse with terrible manners to boot! Thanks, Allie