We took my Nation Show Horse gelding, 14 years old, 'fluffy' at about 1300lbs and my daughter's two year old Arab, lightly 'fluffy' at about 650 lbs and turned them out in the arena before asking them to have any brains. They did thier normal GALLOP and BUCK and PLAY for about 45 mintues. During that time, one zigged while the other zagged and they crashed into each other at a full gallop. We didn't think anything about it at the time and they kept playing.
Not too long after that, the filly, who is really starting to bond with my daughter comes up for loves and we halter both horses. She then took the filly into the round pen to see if they could get a join-up. About three mintues in, no go. My daughter sends her around again and the filly stops dead. Thunk. Won't move.
My daughter (20 so not a kid) see that the filly is not going to push, and works on trust instead. (I had showed her the video from the hog trying thread) She asked her filly to be relaxed about using a rope to lift her front legs. In less than five minutes, the filly was completely relaxed, following her around, and allowing both front legs to be held up with the rope.
Great day training. How about the back feet? She gets the rope down on the right rear and the filly flat refuses to take any weight off of it. Odd... Ask for the left rear and though she will pick it up, the filly is now in a full body sweat and shaking!
I get called in and start at the top of the hip, and work slowly down looking for any 'ouchie' spots. I found none. I picked up the back foot (only her fourth time ever having her back foot picked up) and the whole horse is shaking but not giving me any pinpoint ouchie spots. With a halter on, we asked her to walk for us, but she would not put any weight on the left rear.
About the time, the stable owner and manager wander over. Everyone takes a look but other than a slightly odd stance where she is standing with her back end tucked up under her a bit, she is in a full lather at this point, and shaking, we can't find anythign wrong with her.
I ran my fingers down either side of her spine with a LOT of pressure and got no reaction. However, when asked to move, she wanted to, but simply would not use her back legs. After about half an hour, she would shift what back leg she had weight on, but would not even try to take a step.
We put a blanket on her to keep her from getting cold and fed her a half gram of bute - temporarily just leaving her in the round pen. It was two hours later before we convinced her to slowly walk the 60 feet or so to her stall. Once in her stall, she just sort of got 'stuck' again. Willing to pace back and forth with the front end, but not moving either back foot.
In 40 years of horses, I have never seen a horse just refuse to use both back legs like that. I am going to head out in the morning to see if we can hand walk her. She is only 2 1/2.