Page 108 - Adams and Stashak's Lameness in Horses, 7th Edition

74 Chapter 2

line, and observations made from poll to tail and down Hindlimbs
to the gaskin. The attachment of the appendicular skel­ The hindlimbs are the source of power for propulsion
VetBooks.ir should be observed with emphasis placed on limb and stopping. The hindlimb muscling should be appro­
eton (limbs) to the axial skeleton (head and trunk)
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priate for the type, breed, and use of the horse. The
angles. There is a strong relationship between long
bone lengths and wither heights at differing ages, sug­ croup and points of the hip and buttock should be sym­
gesting that horses should be proportional regardless metrical, and the limbs should be straight and angled
of their size. 1 correctly.
From the front of the horse, the limbs and hooves
are evaluated for straightness and symmetry. The depth
and length of the muscles in the forearm and chest are CONFORMATION COMPONENTS AND TRAITS
observed. Evaluation of balance, top line, and limb Balance
angles is confirmed by viewing the off (right) side of
the horse. Balance refers to the relationship between the fore­
From directly behind the tail, the straightness and hand and hindquarters, between the limbs and the
symmetry of the back, croup, point of the hip, and but­ body, and between the right and the left sides of the body
tock are evaluated along with the hindquarters and the (Figures 2.7–2.9). It is a subjective assessment based on
hindlimbs. This is also the best vantage point for evalu­ the overall conformation of the horse. A well‐balanced
ating back muscling, alignment of the vertebral column, horse is thought to move more efficiently, thereby experi­
and (provided the horse is standing square) left‐to‐right encing less stress on the musculoskeletal system. However,
symmetry. one study that measured multiple conformational traits
The observer should then make another entire circle in racehorses found that 25% of all parameters showed a
around the horse, this time stopping at each quadrant to significant difference between the left‐ and right‐sided
look diagonally across the center of the horse. From the measurements. 40
rear of the horse, the observer should look from the left The center of gravity is a theoretical point in the
hindlimb toward the right forelimb and from the right horse’s body around which the mass of the horse is
hindlimb toward the left forelimb. This angle will often equally distributed. It is located at a point of intersection
reveal abnormalities in the limbs and hooves that were of a vertical line dropped from the highest point of the
missed during the side, front, and rear examinations. withers and a line from the point of the shoulder to the
The horse is then viewed from the front in a similar point of the buttock. The center of gravity is usually just
diagonal approach. While observing the horse, it is help­ behind the xyphoid and two‐thirds the distance down
ful to obtain an overall sense of correctness of each of from the top line of the back (Figure 2.9).
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the four functional sections: head/neck, forelimbs, trunk Although the center of gravity remains relatively con­
(barrel), and hindlimbs. stant when a well‐balanced horse moves, most horses
must learn to rebalance their weight (and that of the
Head and Neck rider and tack) when ridden. To pick up a front foot to
step forward, the horse must shift its weight toward the
The size or shape of the head is often breed specific, rear. The amount of this weight shift depends on the
but does not appear to influence performance or lame­ horse’s conformation, the position of the rider, the gait,
ness. The neck acts as a lever to help regulate the horse’s the degree of collection, and the style of the performance.
balance while moving; therefore, it should be long and The higher the degree of collection, the more the horse
flexible with a slight convex curve to its top line. 9,21 must step under the center of gravity with the hindlimbs.
Jumping horses have been found to benefit from longer If the forehand is proportionately larger than the
necks, probably because they make it easier to maintain hindquarters, particularly if it is associated with a down­
balance over the fence. 21 hill top line, the center of gravity tends to shift forward.
This causes the horse to travel heavy on his front end,
setting the stage for increased concussion, stress, and
Forelimbs lameness. When the forehand and hindquarters are bal­
Kinematic/kinetic studies have confirmed that at the anced and the withers are level with or higher than the
beginning of the stance phase, the distal portion of the level of the croup, the horse’s center of gravity is located
forelimb is subjected to more stress from weight‐bearing more toward the rear. Such a horse can carry more
5,6
forces than the distal portion of the hindlimb. The weight with his hindquarters, thus moving in balance
forelimbs tend to “bounce,” whereas the hindlimbs and exhibiting a lighter, freer motion with the forehand
“slide.” The forelimbs are considered to support than the horse with withers lower than the croup.
21
approximately 60%–65% of the horse’s body weight, so However, hip height was consistently 2–3 cm greater
they should be well muscled and conformed normally. 9,36 than wither height in young growing Thoroughbreds,
suggesting that level top lines may only develop with
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Trunk (Barrel) maturity, if at all. Even with a level top line, if the fore­
hand is heavily muscled in comparison to the hindquar­
The horse should have adequate heart girth and ters, the horse may travel heavy on the forehand.
width (spring) to the ribs to house the vital organs. The A balanced horse has approximately equal lower
back should be well muscled and strong so that the limb length and depth of body. The lower limb length
horse is able to carry the weight of its internal organs (chest floor to the ground) should be equal to the dis­
and the rider and saddle. tance from the chest floor to the top of the withers