The shoulder of the horse is a very misunderstood, yet extremely important area of conformation. The shoulder affects much of the horse's movement, it's balance, it's neck attachment, and is what makes the difference between a bouncy trot, and a wonderful smooth trot. One of the main problems I see in conversations about a horse's shoulder is what exactly the shoulder is.
The mare above is a perfect example of the confusion. Notice the dark varnish mark against the base of her neck? That is not her shoulder angle. See the shape of her shoulder blade just under the skin? Nope, that's not her shoulder angle either. The divot where her neck meets her body? you guessed, not her shoulder angle.
So what IS the shoulder angle then?
The slope of the shoulder is the "angle" that most people refer to when talking about equine conformation. This is not the "shoulder angle" exactly, but it is an important piece of conformation to understand.
Here's a good diagram of what we're going to be talking about:
The slope of the shoulder is what many people refer to as the "shoulder angle". I actually have been known to do this myself. It's easier to say, and kind of flows off the tongue. Technically though, it's not correct, but I'll get to that in a minute.
The Ideal Shoulder Slope
The shoulder slope, or slope of the shoulder (the terms are interchangeable) ideally should be a 45 degree angle, as measured between the top of the withers and the point of the shoulder. The problem is, no one ever talks about what we should measure this angle against. A line does not make an angle. Recently, I came up against this problem when doing a conformation analysis of a young colt. His shoulder looked like it should be "good" to my eye, but my measurements kept telling me that it was all wrong.
The 2 red dots in that image are the palpable points on the horse. This means the parts you can reach your hand up, and feel. The yellow dots are the points we talked about in the previous post, regarding the neck. They come into play as well. The top of the withers, the upper red dot, is often where the mane hair stops growing, but is always the center of the rounded bony wither structure. This is the same place we use to measure our horse's height. The lower red dot is the point of the chest. This is the hard bony point you can feel when you touch your horse.
How to measure Shoulder Slope
When you look at that line though, you can see that it's an imaginary line, and there's no true edge or angle on the horse in that section in real life. This is where a lot of problems come in. Google shoulder angle, and you'll see it. Horses with lines drawn where their neck meets their body, angles that have nothing to do with the shoulder slope, and other random lines placed on ponies through the use of MS Paint and other digital drawing software.
Most often, this line (the one I have depicted in red) is measured against the line of the horizon, or a perfectly horizontal line. So, does that mean that as a horse ages, the horse gets a better or worse shoulder? Well, no. Even though the horse grows, and its relation to the ground changes (hip high, level, shoulder high, and such) the horse's angles stay consistent against its own body. If you do a whole lot of complicated math, measuring and add more colored lines then there are colors to use, well, you can determine the proper angle. Now, the easy way is to measure the horse at a few stages of growth, and average out the results. Another good way is to measure the horse against its structural center of balance.
Now, "eye balling it" I look at Sweetie and tend to think she's a hair straighter then I like in the shoulder. A measurement of 50 degrees sounds just about right to me. Considering that she was at a phase of growth that had her "shoulder high" the measurement makes a bit more sense to me. Since she's only slightly gangly, this angle is only a degree different then if she is measured against the horizontal. In other words, not a big deal in her case.
But if she was at a downhill stage of growth, this measurement would stay pretty much consistent.
This is because if her front legs are short, or her hind ones are long, or her bits and pieces can't figure out where they want to be, her spine still has to run through her shoulder area, across the back, and into the hip. The spine isn't going to be shifting its path in her body, and her hips and shoulder aren't going to be suddenly changing the way they attach to the other bones in her body. Oh sure, she's an ugly mess in the picture above, but structurally, she's still pretty decent.
The actual "shoulder angle" is the angle created from the slop of the shoulder, and the slope of the humerus (upper arm bone, which is located in the chest of a horse). The top red dot is on her withers, the next lowest is at the point of her shoulder, and the lowest red dot there is at the point of her elbow. You can feel the bony part of a horse's elbow, and the range of location varies by conformation.
This angle is determined by the set of the scapula (shoulder blade) in the horse, and the length of the humerus (fore arm bone). For Sweetie, this angle is 87 degrees, and I have to keep in mind that her leg is set slightly back, which will raise the point of elbow slightly.. This angle should ideally be at least 90 degrees, and up to 120 degrees is considered good. The larger this angle is, the easier it will be for her to swing her legs forward, and raise her knees to her chest.
The longer the bone in the forearm, the lower the point of elbow will be, and the larger the angle of the shoulder. The set of the scapula (or slope of shoulder) is not nearly as important on its own, as it is in relation to this angle. A very upright shoulder with a horizontal humerus could result in an angle of 90 degrees or more, and that straight shouldered horse would still be a nice ride, AND be able to haul weight.
The Straight Shoulder
Wait, did I just say something that made it sound like there's a good reason for a straight shoulder? Yep, I sure did!
Back in the day when the horse was the only form of horse power there was, draft horses were used to pull weight. Need a tree stump removed? Just hitch up your power house, and it'll be gone in no time! For these horses, the straight shoulder is ideal.
|Photo: Carol Mitchell|
Look at this lovely hard working Belgian draft here. This is a perfect example of a horse leaning into the harness, and using his conformation to his advantage. He pushes his shoulder blade against the collar, working as a lever against the actual harness, uses his neck to adjust the balance low and forward, and his hips and hind legs are the power to move what ever he is hitched to.
A good way to envision this, is to thing of moving the horse's collar, and the weight attached to it, with a pole. You can either poke the pole in the ground, and heave on it - in which case the point of the pole closest to your hand would move more vertically, leaving the pole in a straight up and down angle when you're done, or you could try to shove the pole under the harness and lift it up, keeping the same sloped angle, but wearing out your arm and back muscles.
The green arrow is the direction of force working against the horse. It is down and back, and the motion of this picture makes it easy to see. The collar is almost perfectly perpendicular to the direction of force. This makes the horse's effort that much more efficient, even though the horse technically has a "bad" and upright shoulder slope.
The Over View
When talking about equine conformation, shoulder is always one of the most talked about things of a horse. Often the horse's shoulder slope is used as proof of the horse's quality, and yet, on its own it means very little.
The angle of the shoulder and upper arm bones is the true measure of a horse's gait. And open (90 degree or greater) angle allows the horse freedom of movement, and a gait that is a pleasure to ride. While this is most commonly found in horses with a shoulder slope between 45 and 50 degrees, it is not exclusive to the slope of the shoulder. The length of the upper arm bone is actually the more important feature.
And while we've been told that a "straight shoulder" is a horrible thing in a horse, few people truly know what that means, or why a straight shoulder even exists. The horse's conformation is not something that can be looked at in bits and pieces, but rather we need to look at a horse as a whole, and measure its form against its function.
The Sugarbush Draft Horse
The ideal Sugarbush Draft Horse is built for riding, and for pulling light carriages. These horses are not typical drafts, and are poorly suited to hauling heavy weights because of their conformation. The ideal shoulder slope is 45 to 50 degrees, with the average SDHR horse being on the high side of "ideal". Much of this is due to the ancestry of other draft breeds - breeds that were bred to pull weight.
The important thing though, is that the Sugarbush Draft has a moderately open shoulder angle. Most SDHR horses have a shoulder angle between 90 and 95 degrees, and breeding for openness between the scapular and humerus is encouraged.
The Sugarbush Draft Horse has a moderate leg action, and a lovely forward extension because of the shape of this angle. This means that the rider feels a smooth, but forward gait under them, with little jarring.