Rollestone, given these mares often drip quite a bit of milk before they actually deliver the foal, is this colostrum rich milk that is being lost or does that kick in during the actual birth of the foal. If you had a mare that was running milk for days on end would she be depleting her colostrum stock?
Spaniel - I've spoken to breeder friends and vets about this and the general consensus is that if it goes on for over 3 or 4 days then you might want to try and milk off some colostrum but a couple of days is ok...
A lot of the really good stuff isn't released until baby arrives so it's normally ok...