I am starting with a very brief synopsis of Goubaux and Barrier’s principles of ‘zootechnics’ to make sure my readers have context. You can find a longer intro by clicking here.
Even though the Exterior of the Horse was published in 1891, it still offers a very different approach from either veterinary pathologists who look for what is wrong after an issue arises or breeders and trainers of the competitive horse industry, who produce horses that sell young rather than horses that stay sound over the long term. Zootechnics is defined through the reciprocal fitness of the all parts of a horse for the work that they are required to do.
In order to define an absolute equine beauty, zootechnics first asks what do specific parts of the horse actually do. In order to define a relative equine beauty, zootechnics then asks how specific proportions and relationships of those parts of the horse affect their ability to perform the work we humans ask of them. In order to answer those questions, Goubaux and Barrier divided the horse into three functional regions, the head and neck, the body, and the limbs.
Goubaux and Barrier define the horse’s limbs as ‘broken columns articulated from space to space, (that) support the body and, by their movements, transport the whole from place to place. The limbs may be further defined by their position, form and function into pairs of fore and hind limbs.
Goubaux and Barrier define the horse’s limbs as ‘broken columns articulated from space to space, (that) support the body and, by their movements, transport the whole from place to place. The limbs may be further defined by their position, form and function into pairs of fore and hind limbs.
- The bones of the hind limbs consist of the sacrum- including the lumbosacral and sacroiliac joints, the pelvis-including the ilium, ischium and hip joint, the femur, the stifle-including the patella, the gaskin, the hock, the cannon bones, the bones of the pastern, fetlock and hoof.
- The function of the hind limbs is to drive the horse’s mass forward horizontally
Zootechnic equine beauty is dynamic. Some beauties are absolutes, required for all horses to be healthy and sound. Other beauties are considered relative, varying depending on what sort of specialized work is demanded of a horse. That means that the beauties of the equine hindquarters vary according to their fitness for the work that the horse is required to do.
Length of croup is considered an absolute beauty with the ideal croup being equal in length to the horse’s body, from the withers thru the loins (the lumbar region). However, simply measuring the croup from the point of the hip to the point of the buttock can be misleading as it ignores the actual biomechanics of the bones. In the hind leg, the axis of movement differs from the axis of form. The axis of movement for the femur begins at the center of the hip joint and then extends to the center of the femoral-tibial articulation in the stifle. When at rest, the slope of the femur combines with the slope of the ilium to create the angle of the hip joint.
- Flexion of the hip joint allows the femur to be brought forward and upward to a horizontal position. Granted, this an extreme closing of the hip joint, such as when a horse decided to scratch their ear with a hind hoof.
- Extension of the femur is limited to its reaching the vertical. Forcing extension beyond the maximum causes injury.
- The amplitude of the horse stride is dictated by the difference between the resting position of the femur and the degrees of extension taking the femur to its vertical limit.
While the length of the croup is usually measured from the point of the hip (ilium) to the point of the buttock (ischium), there several factors that influence the relative beauties of the croup. Because the iliopsoas muscle that brings the femur forward reaches down from the sacrum and ilium, the relationship between the length and slope of the ilium and the length and slope of the femur directly dictates the power and the amplitude of a horse’s stride. The angle between the femur and the ilium varies according to the slope of the femur when the horse is standing at rest as well as the static slope of the ilium.
The vertebrae of the sacrum themselves have the least allowance for movement of the horse’s entire spine. One of their primary functions is to protect the spinal cord and the associated nerves from compression and damage. This protection is even more essential at the lumbo-sacral joint as those vertebrae are required to protect the lumbar enlargement. This enlargement is complex enough to be considered a small brain in its own right. It directly controls the activities of the hind limbs, so the nervous impulses do not have to travel all the way to the horse’s head and back.
The muscles that attach to the vertebral processes on the sacrum help to rotate and stabilize the entire hindquarters as well as extend the femur. The bony levers that define the topline of the croup develop differently as their growth responds to muscular stresses. The top line of the croup varies depending on the height of the vertebral processes as they respond to the efforts of the muscles that:
- Rotate the lumbo-sacral joint
- Stabilize the sacro-iliac joint
- Extend the femur from above the hip joint
Biomechanically, a horse’s abilities can be better ascertained by learning to discern the slope and proportions of the ilium, ischium and femur that dictate the appearance of the croup.
- The proportions of the croup are relative beauties that compare the distance from the point of the hip to the hip joint and the distance from hip joint the point of the buttock.
- The distance from the point of the hip to the hip joint is a relative beauty that depends on the slope of the ilium from the point of the hip to the hip joint. That slope varies between 30o-45o.
Since the relative beauties of the hinquarters vary according to so many different factors, it can be difficult to communicate what you see. Imagining the position of the ilium and femur as hands on an analog clock face may be dated, but I have found it to be a very useful image. Make the short or hour hand of the clock represent the ilium and the long or minute hand represent the femur. Since the hands are moving clockwise, the horse is facing left.
- The slope of the ilium may vary between a more horizontal 30o or 10 o’clock and a more sloping 45o or 11 o’clock
- The standing position of the femur when the horse is at rest may vary between a more vertical 7 o’clock and a more horizontal 8 o’clock
- 6 o’clock is the femur’s vertical limit of extension.
- 9 o’clock is the femurs horizontal limit of flexion
I have also found the way types of horses were defined by use in old cavalry manuals and Baroque texts helpful. When horses were essential, the relative beauties of the hinquarters of sound serviceable horses who stood up to the work demanded of them tended to vary in these patterns. From left to right, are the Square Horse selected for endurance and agility, the Rectangular Galloper selected for speed on the flat and the Trotter selected for work in harness:
I have done my very best to limit the number of variables, so to the best of Microsoft’s ability, the length of lines of the same color are the same in each figure. The distance from the top to the bottom of all three figures is the same. The ilium is blue, the ischium is yellow and the femur is red.
While we are told that the ideal slope for the pastern and hoof is always 45o, the angle of the hoof and pastern is actually a relative beauty that should reflect the slope of the femur if the horse is to remain sound. So the short yellow line at the base of the limb reflects that zootechnic dynamic.
The single change I had to make was to lengthen the green line of the gaskin in the Square Horse in order for their cannon and pastern to be correctly positioned. The pronounced slope of the ilium and the femur bring the stifle forward even when the horse is standing at rest.
Those who have questions about how the information in these posts can be pragmatically applied to schooling their horses can find detailed descriptions and instructions in my horse training series, Light in the Saddle. Those want to discuss the implication of these posts on work under saddle are welcome to join my Facebook group aimed at trainers and serious riders, The Isometric Rider.
sara annon 