weaning and drying up mare

Question
I, too, have a 6 mo. colt and mom living during the day along with Grandmom and uncle in a large pasture. At night mom and baby are in separate paddocks from Grandmom and uncle.

Recently, I have tried a few nights with everyone together in the same larger paddock.  Uncle foundered 6 mos ago so he's managed a bit more dearly than free roaming everyone else and his hay is not as rich, therefore, he's not the ideal companion for weaning. I've never seen him nurse his grandmom, but she did  start lactating from one nipple earlier in the season after the colt was born. She doesn't appear to be lactating now, should I risk making her a weaning companion?

How long would I have to keep mom and baby separated before allowing them to pasture together again?

Are there any risks in letting mom decide when to wean him on her own as long as she doesn't need to go anywhere?

Even though I handle the colt regularly and he tolerates short breaks from mom, when they reunite he goes straight to nursing. I have cut back her ration, but he's not all that hungry for grain.  Currently he's about 380 lb. and is eating about 1 pound of a mixture of crimped oats and soaked beet pulp a day along with good quality hay. Does he need to eat more than that before attempting to wean?  

Answer
It will take a week for your mare to dry up if you keep her in a "dry lot" (no access to grass) and only give her hay for a week.  If her bags get really sore, hot and swollen the first day or two, you might use a gentle spray from the hose and use cool water to ease the pain and pressure.  
It should not be a problem to have your colt in the same pasture with the grandmom and uncle.  Both horses are used to the colt's presence and the colt will take comfort from them with his dam being taken away.  As to his nursing as soon as you return him, that is more of a security issue than need for sustinance.  You don't say what breed but I feed a 16% protein to all growing, pregnant or using stallions.  If your colt looks good and is growing well, don't make changes.  You do need to insure that the calcium/phosphorus ratio is equal for the colt.
    I don't know how long you will have to keep the colt separate from the dam but I would venture to guess at least 3 or 4 months.  We don't re-introduce our weanlings back into the main mare band until they are yearlings.  
    If your mare is not pregnant it will not harm either her or the colt to leave them together until the mare weans the foal.  Good luck.