That looks pretty good The neck has to be one of the toughest things to draw when you're starting out. I hope that I can help; I paint horses, and literally spend my whole workday doodling them (boring computer desk-job..)
I have found though, that with a horse head portrait, that moving one thing, often means that everything else has to be adjusted too. Alot of my horse paintings have a LOT of eraser marks underneath the paint!
I would just move the bottom neck line up more, maybe even to the point where the lower jowl area meets the underside of the head. It'd look pretty if the mane were on the other side of the neck but still visible in wisps under the neck. With the forelock blowing off to the right..