Several thoughts here.
First of all, some stallions are not nice (ill-mannered) to the mares and like to chase them around whether they need to be bred or not. Usually, it is the younger stallions that haven't learned their manners yet, but some older stallions do it too. Also, there is some concern that the stallions won't accept the new baby as part of the herd, and may stomp it or bite it, especially while the mare is still trying to give birth, or is still trying to get her feet back under her shortly after giving birth.
If the mare is in with a group of other mares while foaling, it can really stress her out if the area isn't big enough for her to get away and have some privacy. The other mares get all curious and hover around and the new momma feels she has to jump up and defend her baby. If you have the space, and can pull it off, it is nicer for the foaling mare, and safer for the new babe, if you can give them some privacy. They are still going to have their baby whether there is a crowd or not, it just eliminates some of the stress and danger if you can get them alone before foaling.
Secondly, maiden mares don't always read the "rulebook". I have had two or three over the years that didn't produce a drop of milk until the babe actually hit the ground. Their belly shape and size doesn't cooperate either as they have not had those tummy muscles stretched out yet. They don't always get that nice pronounced "V" profile to show the foal has dropped. The more babies they have, the easier it is to tell what stage they are in. Your little gal may just be hiding it well. Especially if she is in good shape!
Thirdly, I had a mare that went into full blown labor once. All the signs, shaking, sweating, biting and kicking sides, rolling, huge bag dripping milk. A bad storm came in and the mare slowly settled down, and everything quit. The vet said that, to some extent, a mare can shut down her delivery if she feels the situation is dangerous, and the storm must have caused this mare to do just that. Within a week the mare's bag had dried completely up, she looked thin as can be. No sign she was ever pregnant. Vet said, must have been a false pregnancy. I put her in with a stallion to get bred back, and she was bred several times. One full month after the night she went into labor she had a beautiful little filly! Figure THAT one out!
Since then I have had my stallion (a young one) show interest in mares that go ahead and foal a week or two later. I think that maybe as their hormone levels change as they get ready to foal, the stallion senses it. Just like he does when their hormones change as they go into heat. I've never had another mare that let herself get bred just before foaling like that one did, but I have had stallions get interested. Maybe that is what your mare and stallion are doing.
Finally, in my experience, mares can have a situation that sure acts like a false pregnancy. Don't know what else to call it. When it happened to us, I had two different vets come out. In this case it was a mare that had foaled for 8 years in a row. She never came into heat after foaling one year and I decided to give her the year off. She was never near a stallion from several months before she foaled that last time, until a year later. That following spring her belly swelled up (although not as big as when she really was pregnant) and she had tons of milk. We were trying to figure out how she could have gotten bred through a fence or something. The other mare that she was pastured with foaled and she tried like crazy to steal that baby. Within a week or two of that other mare foaling, she dried up and got on with her life. A few months later, she was bred, and she had a nice little foal for us the next year. Both vets told us that this can happen in situations where you have an older mare that has had lots of babies. Her body just follows its regular pattern whether she is in foal or not. I have no idea what hormones have to be out of whack to have this happen, but clearly something was off for a year, and then, just as clearly, fixed itself the next year when she had a normal pregnancy and delivery. The vets said it is more common in older horses, so it would be unlikely that your maiden mare is going through it.
Hopefully, your little gal is just not showing all the signs like a more experienced mare would. With any luck, you will have a baby on the ground soon!
