http://standardbredhorses.yuku.com/topic/460
I thought I'd summarize this in one place and then just point to it.
The shoulder slope is determined by drawing a line from the point of wither to the point of shoulder and then measuring that line against the horizon. "Slope" is always measured against the horizon and involves only one bone. The range of shoulder slope in the horse is 40 - 60 degrees, with the majority of horses falling between 45-55 degrees.
45 degrees is a "laidback" shoulder, 55 degrees is an "upright" shoulder.
A laidback shoulder MAY indicate a lower, more rounded action.
An upright shoulder MAY indicate higher knee action, more concussive stride, more choppy stride.
The shoulder angle is determined by measuring the angle of the joint created at the point of the shoulder between the wither-to-shoulder line (the scapula) and the shoulder-to-elbow line (the humerus). "Angles" are created at joints.
90 degrees is an "adequate" shoulder angle.
Less than 90 degrees is a 'closed' shoulder
More than 90 degrees is an 'open' shoulder.
An open shoulder angle MAY indicate freer action.
A closed shoulder angle is least desirable when it comes with an upright shoulder. It is not as serious a fault when the shoulder is laid back.
The length of the humerus is calculated in relation to the shoulder blade reported in percent. The longer the humerus the more scope to the horses' gait. That is, greater reach, arc and lateral movement. The shorter the humerus the more choppy the stride. A humerus is considered long, when it is greater than 50% of the length of the shoulder blade, longer is even better.
Shoulder summary for example:
Laidback shoulder + Open shoulder angle + long humerus= desirable in dressage-type activities
Laidback shoulder + closed shoulder angle + long humerus = ok for most low level disciplines
Upright shoulder + Open shoulder angle + long humerus = desirable in jumping-type activities
Uprght shoulder + closed shoulder angle + short humerus = not desirable for anything, high potential for choppy stride.
In request for a photo illustration. You are looking at only 2 lines for this.
This horse has a 55 degree shoulder slope (line goes from point of withers to point of shoulder measured against the horizon) - upright shoulder
A 78 degree shoulder angle (use the first line, plus the line that goes from the point of shoulder to the elbow) - closed shoulder angle.
Humerus length is 61% the length of the shoulder blade - good length.
