Lee Ziegler, author of Easy Gaited Horses, tells us that ewe neck is when a horse has high head carriage, overdeveloped lower side of neck (often bowing
out) underdeveloped topside of neck, hollow or dip in front of the withers
(pronounced). The exeternal appearance can be from muscle misuse -- but it often
also reflects the curve in the underlying vertebrae of the neck.
neck has a shallow S shape, light bend in the upper part, very slightly more
curve to the lower part of the S.
A ewe neck always has a more pronounced curve
in the lower part of the S (the part closer to the shoulders) and may have a
shallow or slightly more pronounced curve to the upper part, as well.
Interestingly enough, a ewe neck while it may appear to be set "high" and results in
a horse that carries a relatively high head, actually attaches to the body
lower than a "normal" neck.
Q: Is it a conformation point only?
A: Both -- you can only do so much with a neck that is conformed as a ewe neck
by riding, because the underlying bone structure limits how much muscle
development can be done.
Q: or is it the set of the neck by the rider?
A: Can be -- you can take a nice, well conformed neck, and hollow it out by
riding technique. not something I recommend, however!
Q: or both?
A: Definitely both, but the bone structure under it makes it a
difficult job to "unewe" a neck -- can be done.