12 year old Thoroughbred/Quarter Horse mare bucks when mounted?

I would have the vet give her a going over to see if he finds anything unusual and have him check to make sure she is not a bit more than 6 months along they could have gotten the dates mixed up and she could be close to 9 months or more and the foal may be turned in a way it hurts her when saddled I know that is not a usual thing but I had it happen to one of my trail mares when she was about 8 months pregnant and she bucked me off so I had the vet check her and he said the foal was turning and it hurt her to have a saddle and weight on her, we thought she was going to have twins because she had before and raised both and neither was stunted but we supplemented her milk with Goats milk.

it's still a saddle pain issue.

a horse that bucks the moment you sit, is in pain. you're driving the saddle into the withers and that hurts like hell.

get a saddle fitter to figure out what the trouble is, or do enough research to do it yourself.

sorry, but sounds like you don't know enough about saddles to be sure that yours isn't the issue. because it is.

How do I know?

Easiest money I ever made as a trainer:

I was called to fix the exact same problem you have. These people bought a horse from a guy who swore that the mare never bucked.

Well, this mare bucked off the new owner's husband and his friends (they kept taking turns getting in the saddle)

And they finally stopped when the husband landed wrong and broke his wrist.

I went out there, and they had the mare saddled. She looked scared already. I just moved the saddle a bit, and she humped up. I took the saddle off, and put MY saddle on her (because my saddle has a better pitch, wider gullet) and

then I moved the mare around, wiggled the saddle, did some simple ground work so she could feel the saddle.

Then when she relaxed, I got on.

I walked, trotted, and loped her.

She never bucked and she was calm.

It took 45 minutes total for the entire lesson.

Easiest money.

Find someone who knows about saddles to find you the perfect fit.

Also, talk to a chiropractor to come out and adjust her if needed.

____

ALL THAT SAID:

if she's pregnant, it may make being saddled/ridden very uncomfortable for her. every horse is different.

you need to talk to a vet.

Three things:

1) How do you KNOW she'd been broken to saddle? Maybe the reason she was abandoned in the first place is that her previous owners also had been unable to stay on her back.

2) You need to have a veterinarian and/or chiropractor evaluate her. If it's not the saddle or a lack of training, she could be in pain. It may be a pregnancy-related issue, or something else entirely.

3) You should still be able to do ground work and basic desensitization with her if she's pregnant. I don't see how that would stress her. PAIN, however, will....see Answer 2.

She probably is reacting to the massive saddle and maybe the fit. I guarantee that she is not accustomed to all that junk on her back.

I strongly suggest that you borrow an English saddle, or at least a lighter endurance model. Make sure she does not have an injury; if her back hurts, she is not going to want weight on it.

As your different answer mentioned assess with a horse chiropractor. My daughter purchased a horse out of a meat pen he used to be alleged to be broke when she would go to get on he would buck. Turned out his hip used to be out now he's a ideal gentleman!!! Just right luck!

possible nerve damage somewhere in the back or whithers. thermal imaging photos would tell you for sure.