Page 112 - Adams and Stashak's Lameness in Horses, 7th Edition

78 Chapter 2

substance is described by the type, thickness, and length
of the muscle and the position of attachment. Other sub­
VetBooks.ir horse, size of the hoofs, depth of the heart girth and
stance factors include weight of the horse, height of the
flank, and spring of rib.
“Spring of rib,” which is best viewed from the rear,
refers to the curvature of the ribs. In addition to provid­
ing room for the heart, lungs, and digestive tract, a well‐
sprung rib cage provides a natural, comfortable place
for a rider’s legs. A slab‐sided horse with a shallow heart
girth is difficult to sit upon properly; an extremely wide‐
barreled horse can be stressful to the rider’s legs.
“Substance of bone” refers to adequacy of the bone
to the horse’s weight ratio. Traditionally, the circumfer­
ence around the cannon bone just below the carpus
serves as the measurement for substance of bone. For
riding horses, an adequate ratio is approximately 0.7
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inches of bone for every 100 lbs of body weight. Using
this rule, a 1,200‐lb. horse should have an 8.4‐inch can­
non bone circumference.

Correctness of Angles and Structures
A B
The correct alignment of the skeletal components
provides the framework for muscular attachments. The Figure 2.11. Cranial and lateral views of normal forelimbs. (A) A
length and slope to the shoulder, arm, forearm, croup, line dropped from the point of the shoulder joint should bisect the
hip, stifle, and pasterns should be appropriate and work limb. (B) A line dropped from the tuber spinae of the scapula should
bisect the limb down to the fetlock and end at the heel bulbs.
well together. There should be a straight alignment of
bones when viewed from the front and rear, large clean
joints, high‐quality hoof horn, adequate height and the forearm muscles help a horse to move its limbs later­
width of heel, concave sole, and adequate hoof size. ally and medially and to elevate the forelimb. It is
believed by some horseman that long forearms and
short cannon bones are conducive to speed, but this
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Forelimbs has not been documented. 29
The carpal joints should be balanced and should not
Cranial View
deviate toward, or away from, one another. The cannon
Both forelimbs should be of equal length and size and bone should be centered under the carpus and not to the
should appear to bear equal weight when the horse is lateral side (bench knees). Deviations from a straight
standing squarely. A line dropped from the point of the limb may cause strain on the collateral support struc­
shoulder (middle of the scapulohumeral joint) to the tures and asymmetrical loading (compression) of the
ground should bisect the limb. The manner in which the hinge joints in the forelimb.
shoulder blade and arm (humerus) are conformed and
attach to the chest often dictates the alignment of the lower
limb. Whether the toes point in or out is often related to lateral View
upper limb structures, which is why it may be counterpro­ When viewed from the side, limbs should exhibit a
ductive to alter a limb’s alignment through radical hoof composite of moderate angles so that shock absorption
adjustments. The toes should point forward, and the width is efficient (Figure 2.12). The shoulder angle is meas­
of the feet on the ground should be the same as the width ured along the spine of the scapula, from the point of
at the origin of the limbs in the chest (Figure 2.11). the shoulder to the point of the withers. The angle of
The medial/lateral (ML) slope of the humerus is eval­ the scapula and shoulder tend to increase (become more
1
uated by finding the point of the shoulder and a spot in upright) as horses mature from foals to adults. The
front of the point of the elbow on each side. The four shorter and straighter the shoulder, the shorter and
points are then connected visually. If the resulting box is quicker the stride, and the more stress and concussion
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square, the humerus lies in an ideal position for straight that is transmitted to the limb. Studies in dressage
lower limbs. If the bottom of the box is wider, the horse horses and show jumpers have found that a more hori­
may toe in and travel with loose elbows and paddle. If zontal scapula was related to a higher level of perfor­
the bottom of the box is narrower, the horse will prob­ mance. 22,27 Also important is the angle the shoulder
ably toe out, have tight elbows, and wing in. makes with the arm, which should be at least 90°.
The muscles of the forearm (antebrachium) should Horses with a more horizontally positioned scapula or
extend to the knee, tapering gradually rather than end­ a more flexed shoulder joint show more maximal exten­
ing abruptly a few inches above the knee. This is believed sion of the elbow joint relative to the angle at initial
to allow the horse to use its front limbs in a smooth, ground contact. This prolongs the stance phase. A long
5
sweeping, forward motion. The pectoral muscles should sloping scapula is ergonomically efficient and is thought
also extend far down onto the limb. The pectoral and to place the rider more to the rear of the horse, resulting