Mare gestation lengths vary considerably. So, although she may be due in 10 days, she may be five to 10 days early or late depending on the sex of the foal (colts are carried five days longer than fillies), temperature, and season. Mares also have a natural variation in gestation length, time of bagging up, etc. Additionally, it is not uncommon for a maiden mare not to have udder development prior to foaling. She may not have much udder development until the time of foaling or shortly thereafter. As a precautionary measure, you might locate a source of frozen colostrum just in case the mare doesn't produce much milk early on. However, if the mare has been grazing fescue, this might prevent her from having normal udder development. If she is still on pasture, you might remove her and feed her a grain mix and hay. It is always a good idea with maiden mares to be present when they foal in case some assistance is needed.