Originally Posted by riccil0ve
I imagine they are just establishing hierarchy, but I would also take the halters off. It is too easy to get stuck on fences, trees, etc. I've heard of a horse get it's hoof stuck in it halter from bringing it's hind leg up to scratch their face like a dog does. She broke her neck. I don't mean to scare you, I just want you to see that it is a serious matter to leave halters on. The mare I mentioned was in her stall.
ETA: Mares also establish hierarchy, usandpets. You forget that wild herds do have an alpha mare.
I caution stepping in, though. There is no reason to get hurt. Maybe feed them further away from each, but unless these horses have superb respect for you, I wouldn't get in the middle of a horse fight any sooner than I'd get in the middle if a dog fight. O_o
No I didn't forget that there's an alpha mare, but mares usually don't play. If it's establishing a hierarchy, they wouldn't be nipping at the halters. They would be biting at the neck, legs or sides but more likely kicking. They would likely leave serious marks. When playing, they may make contact but not really bad marks.
As for the stepping in, maybe I misunderstood what she meant. When we feed ours they are next to each other but in seperate stalls but close enough to make contact, such as biting. If she is feeding them in the pasture then I wouldn't step in. I would let them settle it on their own or seperate them at feeding time. I have fed our in the pasture by spreading out their bowls but I would have to 'protect' our youngest mare. The others would make her move away from her bowl and take her food. They learned that it's best not to challenge me though.