pregnant or not?

Question
My daughter has a 13yr old mare that she has had about 5 months. After about a month she was putting on a lot of weight so we had the vet check her.He examined her and said he could feel a foot and she was at least 5/6 months pregnant. She has steadily been putting on weight but yesterday she was out in the field when our riding instructor saw her lifting her tail to the geldings as if she was in season. I asked the vet to check her again and a different one came, examined her and said she could not feel a foal. She said that although she could not be 100% she didn't think that our mare was in foal. She said she may have been and the foal has died and may have been reasorbed or have mummified and is still in her. Obviously my daughter whose 14 found this quite distressing. Could you tell me if you have ever heard of this and advise me what to do next. When you look at her she is very large and when she is very still you can still see something moving in her stomach just in front of her rear leg behind her ribs in the area where the coat separates in different directions. We are completely baffled. Thank you.

Answer
Hi-I haven't heard of this before so I can't give you a definite answer on this. the 2nd vet could be right about the foal inside of her-the foal could have died and she hasn't passed it yet. I would get a thorough vet check to see what that bulge is. It sounds to me like she is going through a false pregnancy-the mares gain weight, drop their milk and appear to be pregnant for the whole time-the flagging of the mare to the geldings is what makes me think that. I hope this helps and good luck with her. Thanks