Mare, 10 yo, excellent health, out of shape due to almost 2 years of pasture puff-dom. Moved 3 weeks ago to new barn. I'm now riding 4-5 days a week, 90% trail and hill work, 10% arena. Mare is always happy to go, easy to bridle, ready to run.
About 30 minutes out, mare starts head shaking and it continues for balance of ride. Mostly at the walk, but she'll do it at trot and canter as well. I've been off roughly 1,000 times now (okay, maybe not THAT many, but plenty) checking bridle, ears, bugs, bit, etc etc etc. Riding buddy has ridden alongside at all gaits and does not see anything bothering.
Bridle or bit does not matter. We've been through several combos. No bit (bosal) does not matter. She shakes her head, sometimes to the point that she'll stumble because she's not paying attention.
I have looked at eyes, ears (she always loves to have her ears itched, but that's not new), throat, yada yada yada.
Saddle is all purpose, has been her saddle for past 3 years, no new pad, girth, or breast collar. No soreness that I can find after riding anywhere. She has always wanted the sides of her face rubbed when the bridle comes off, but that's not new nor does which bridle matter.
No change in shoeing. Tack is kept reasonably clean; I wipe it down with a damp towel regularly.
All I can come up with is 1) something in her ears, but I can't find it; 2) some kind of allergy -- although she does not do the head shaking in the day pasture or night paddock, or 3) po'd at being ridden much more now, although she's always happy to stride on out.
I do have a call into the vet, but figure you guys will have some input that I haven't thought of.
When you've been falling/bailing off horses for 40 years, you're really good at it!
I have one with headshaking syndrome, but he generally does it the whole time. So fingers crossed for you that it's not that! Mine acts like he has something disgusting on his face and can't possibly go on without rubbing his nose on his legs, but some of them do act like they have a bug up their nose. Could it be partly fitness related? If she's been off for several years, three weeks is not a very long time to be riding for more than half an hour.
My gelding is a fly drama queen...he can't stand them. For him the worst seems to be gnats/flies on his nose. I use the Cashel lightweight riding fly mask on him when I ride, the one with the full face coverage. He's a big warmblood and I use the draft size to get the longer nose coverage. Tadaa! No head shaking.
It got annoying, he'd be so busy shaking his head he'd stumble. There were times he'd walk and have his nose on the ground rubbing off whatever flying varmint was bothering him.
Try a full face mask...Cashel also makes a nose only mask that goes on the noseband of the bridle. Some horses are just very sensitive.
Could you describe exactly how he "shakes"? Genuine headshakers who are "shaking" because of inflammation of the trigeminal nerve in the face have a rather distinct up and down "bob" which is very sudden and quick, and very similar to someone startling when they're stung by a bug.