Not personally because if my mares were bred I knew it but it does happen, that unexpected pregnancy. In a word, yes, the important thing to do now is talk to a nutritionist or vet or even here and get the necessary info you need to bring her up to weight gently. Some mares are taken down by being in foal thus the need for good feed. Answers to questions like...how old a mare, first baby or an old timer, what do you feed now, and is she is and out or out 24/7, up to date on worming, shots, when is she due? Listen to those who choose to post for you. A picture of the mare could also help those of us with helping you with the feed necessary to bring her up.