Sudden change in mares behaviour

[jules9203]

This is a long one - Sorry but really need some help!!!
I bought my mare as a 5yr old and for the first 5 yrs she was on part livery. She was turned out with a field of mares that changed on a regular basis. She had no issues with the other mares and was never particularly challanging to others. A few years ago another horse, who I'll call 'M' was introduced. She was a youngster and my mare took her under her wing and they got on well. Last January I was able to move my mare onto diy on the same yard. This meant changing paddocks and being turned out with another set of mares. There were no problems and they have all been calm through out the last 9 months. Last week 'M' was moved onto the diy yard and turned out in the same field. My mare has taken a huge dislike to her to the extent that if she sees 'M' across the field she will suddenly take off teeth barred toward her and chase her away. It is not easing off and I am at a loss as what to do. No one has been hurt but 'M' is now terrified of her and I have never seen my mare react this way. She even tries to go for 'M' when we are riding and she is near.
Any views / ideas / tips greatfully received. I cannot change paddocks and individual grazing is not an option at the yard.

 

[Black_Horse_White]

Seems to me that your mare maybe quite high in the pecking order in her group, and is keeping M away from the rest of the herd. They should settle down eventually. Or I could be talking utter tosh, if so take no notice of me 

 

[jules9203]

She has been second 'in line'. Fingers x I hope ur right

 

[Spring Feather]

I think Blackhorsewhite is not talking utter tosh I think that is exactly the problem, I've seen it lots of times, and they always settle down eventually. So long as your field is large enough that M can get away without being injured or pinned in a corner all should calm down soon.

 

[jules9203]

Thanks - there is plenty of room for the other mare to get out the way, so fingers crossed it all calms down soon !

 

[classicalfan]

Just as an add-on to the other comments. It seems to me that your mare is acting very much like some 'mums' do - driving her daughter away from the group. Once M learns to keep ehr distance everything should settle down - confusing for her , though, bless her!

By the by, geldings will do it to when they have had enough of being an uncle to a younger horse.