My foals NEVER call when they are separated for a while- the mares call more than the foals!!! The foals have one another and the feed, so they play and eat, and never worry. I build it up- to start with the mares come in with the foals and stand tied, then the mares get taken out when the foals are settled, but stand outside the round pen trying to steal the feed (!) Then the mares are moved to the field next door where they have better grazing so they hang around the gate then wander off and graze. Some of my foals are near weaning, the first two will come off this week or next, I think, I do not expect any calling- the mares are milked out before the foals return so the mares are comfy and the foals get no "hot" milk, this helps weaning to seem more natural.