I thought I had my saddle fitting woes finally solved... sigh.

After last year's frustrations, I finally found a saddle that fit my difficult Arab. He has high withers and a swayback, but also a reasonably well-sprung ribcage and large shoulder. I ended up with a Thorowgood endurance saddle, which has an adjustable gullet, and had it professionally fitted. I'm using a thinline pad with bridging inserts to help with the swayback, and the saddle has great wither clearance even with the medium/wide gullet.

He's been going spectacularly in it for about 5 weeks -- no more sore back and no more spooky beast. We did a brisk 8 miles on Saturday, and it was the first time I've ever been able to trot/canter in a group on a loose rein.

And then there was yesterday. He was spectacularly awful! Spooking, sucking back, crooked, etc. I rode on my usual trails, only 10 miles at a very relaxed pace. When I took the saddle off, he was really sore, with a big dry spot right behind his withers on the left, and sweaty ridged hair behind that.

Here's my theory...

I've been racking my brain to figure out what I did differently yesterday. The only thing I can think of is that I took a shortcut that I hardly ever take, which goes down a very steep hill within the first few hundred yards of leaving the barn. In fact, I haven't gone that way since I got the new saddle (and now I think I may be an idiot for not realizing this last year, when I used this shortcut all the time). So I'm wondering if going down this hill at the very beginning of my ride caused the saddle to slip forward and stay there for the rest of the ride, pinching his withers. It's not any steeper than other hills that I do later in the ride, but by then he's warmed up, and the pad is a little sweaty and sticking in place.

Does this make sense? Has anyone else noticed anything similar, or can you think of anything else I missed?