Sounds like a diet issue.  You would see additional symptoms if the animal was in pain or had a medical condition.

I would be very cautious about rich hays with lots of clover and alfalfa, and all the many high density pellets, prepared feed mixes and 'ration balancers'.  My old fellow turns into a raving lunatic on most of the very popular new horse feeds and ration balancers.

Solaris:

Also, if you can put this horse on 24/7 turnout it will be a BIG help to arthritis.

There is the post I was looking for.  I have had problems with arthritis in my knees and even sitting for too long can make them hurt like crazy when I first start moving again.  It is a possibility that with all the issues your mare has had that being kept in even half the day could be making her get too stiff.

I rode a mule for someone the other day that was a sixteen year old that had been trail rode in the mountains since he was 4.  Just watching him I could tell he had some arthritis in his back hip.  When I lunged him he was great, moved without a problem and flexed well.  However when I got on him he was rushy in the trot, wouldn't neck rein or flex and had his head up in the air bracing his back.  So I got off and put my friends 6 yr old granddaughter up there and he neckreined, trotted off and was a much different mule.  It was my weight which caused his arthritic hips to hurt so he was reacting to the pain.  If the mule was mine I would put him on Cetyl M and just do short trail rides on him.

ponypower24:

The massage therapist is coming out on Saturday (hopefully!) or Tuesday

Well?  And?  So?  What happened? 

 The massage therapist's car broke down Saturday (of course), so Piper has yet to get her massage. Sigh. I'm so frustrated.

 I've just been lunging her for the past week, but I decided to get on a bit today. We probably walked for 10 minutes and trotted for five ... and she was good! Not super relaxed, but not fighting me at all or trying to take off. So I got off  and ended on a good note.

 I used a different half pad that I used to always use on her. It's one of those black Miller foam pads. I had switched over to a fleece half pad and thought maybe that was causing the saddle to pinch her, so maybe she was feeling better with her old pad back?

 At this point I'm anxiously awaiting her vet appointment next Wednesday, Oct. 7. She will be getting her teeth done, eyes checked and an overall soundness exam. She's been sore on her left front, which is the leg with the old tendon injury.

In the meantime, I'm stuck waiting until the massage therapist can start making appointments again.

Also, because someone asked, she gets about four pounds of Purina Equine Senior both AM and PM and free choice grass hay, plus her grazing time. It's specially formulated to keep weight on seniors without making them crazy, so I don't think that's the problem. I actually did try cutting her grain in half awhile ago to see if that helped, and it only made her start losing weight.

Someone else mentioned it might be me being tense, which I think is a definite possibility. However, I ride other horses at the farm, including a very nervous and spooky 5yo, and she doesn't react negatively to me. But it's possible I get on her expecting her to be bad, so she is. I've tried to really be "zen" before I get on and not stressed or rushed. 

 I do really wish I could move her to a place with 24/7 turnout. I love the farm where she is, but she can't get that kind of turnout there. Maybe that's what this will come down to ...

 Well, rats.  I was hoping you would have some more information by now. 

Sounds like what you are doing is good for both of you, until you can get her fully checked out by the vet.  The different pad may have helped, but there still is some underlying problem.  

So, I'll have to wait until October 7 for an update.  I'll try to be patient....

She is very cute - thanks for sharing the photo!

 I think you might want to add a selenium/vit E supplement.  I have several horses that just get nervy without it. One tends to jig on the trail. become ewe necked and and bit of a run oof.  My vet suggested trying the selenium and E and he is a much better horse and it is not expensive.  His blood test was OK but slightly low.

I have three questions:

1. Did she have a close companion that she is now separated from?

2. Does she seem to get along with the other horses in the barn or has her pecking order changed for the worse?

3. Are the barn staff and owners professional and do they treat the horses well?

I have seen all three of these affect horses.

Your horse looks happy and relaxed in the picture and so do you. I hope you find a good resolution.

 Its pain... go to a vet, horse chiropractor, etc. and find the source of the problem.  Or it may be that her body has just reached the point where being ridden causes too much discomfort, but either way your story screams I HURT!