Lame behind at walk but not trot - experiences/ideas?

[JillA]

I don't usually post for lameness problems, as I reckon it is a job for a vet. But a veteran mare (25yrs) here will have a vet visit before long, so just looking for experiences.
She is lame behind at walk, in that she goes with a very short stride on her off hind. She seems to bear almost the same weight as the near hind, and no head nodding, it's just stride length - at trot it is barely noticable but at walk the stride is only half the length of the other. She has been out of work all winter, so rest doesn't help, and just bringing back into light work - it is worse after being ridden for 10 minutes yesterday.
Bone spavin? Not typical but could be, or some other degenerative joint disease, and maybe support with Danilon will be the best we can acheive at her age.
Anyone else had a similar experience, and did the horse come sound enough for light work?

 

[LittleBlackMule]

If she were mine I'd get a physio out to check her pelvis.

 

[TheMule]

Is her trot step normal length?
Normally this eould suggest bilaterl lameness to me

 

[Mongoose11]

I will be watching this with interest. My mare has a very slightly shorter stride on her off hind in walk, but perfect in all other gaits. Others can't see it. No issue with work whatsoever and doesn't get worse, shows no 'lameness' other than this very fractionally shorter stride..... Back is perfect..

Keep threatening a full work up, but people think I am mad.

 

[Tiffany]

Does her stride in walk improve when she's been walking for a few minutes? At 25 she's likely to have a little arthritis and stiffness so could just be an age thing which means she takes longer to loosen up.