We have a maiden mare that is overdue (today is day 368!!), she has been developing normally, looks pregnant, we've seen and felt the foal move, has a small udder and hasn't shown any signs of heat since she was bred........until yesterday! She was squatting and peeing in front of the stallion's stall! We hand breed so our dates are definite-the last day that she took the stallion was June 28. When our vet was out last week to do teeth on some of the others, she looked at her from the doorway and said not to get too worried about not having a foal yet, and that it definitely looked like she was in foal. We've done the nail test on her all along and we are still getting the same result that she is carrying a colt (we've had the nail be wrong on the sex but have never had it be wrong on in foal or not-a few years ago on a different mare, the nail said not in foal but the blood test the vet done said in foal and it ended up that the mare wasn't in foal)! So, is it possible for a very pregnant mare to suddenly start to show heat signs?