Decreased sensory nerve input that occurs in some cases of neurologic disease.
As you might imagine, a horse that cannot accurately perceive the location or movement of one or more limbs is destined to trip on occasion.
Instigator: Unwillingness to achieve maximum stride height—the horse voluntarily avoids normal flexion of the limb.
Possible Underlying Circumstance(s)
Comments
Joint pain, especially when associated with the carpus, elbow, shoulder, stifle, and/or fetlocks.
Some joints undergo considerable flexion during protraction of the limb. Since joint pain is usually exacerbated upon increased flexion, most horses will resist bending the respective limb(s) as much as possible when one or more of these joints is affected. This, in turn, makes them much less likely to clear the ground surface and more likely to trip.
Muscle pain, especially when associated with the brachiocephalicus, biceps brachii, quadriceps femoris, and extensor musculature.
Certain muscles function to raise and/or protract the horse’s limb, either through direct or indirect means. Most animals will choose to disengage these muscles when they’re sore, thus inhibiting their ability to clear the ground surface and/or complete a full stride with the affected limb(s).
Instigator: Inability to achieve maximum stride height—the horse is not able to achieve normal flexion of the limb.
Possible Underlying Circumstance(s)
Comments
Muscle fibrosis (scarring), especially when associated with the brachioce-phalicus, biceps brachii, quadriceps femoris, and extensor musculature.
When scar tissue replaces normal muscle fibers, some functionality of the structure is relinquished. Horses will be more likely to trip if certain muscles cannot be adequately employed to raise or protract the horse’s limb.
Inadequate muscle strength, especially when associated with the brachiocephalicus, biceps brachii, quadriceps femoris, and extensor musculature.
Horses will sometimes encounter a loss of muscle strength and function when they are debilitated due to metabolic issues such as chronic infection, pneumonia, myopathy, and malnutrition. These horses may be forced to exert increased effort in order to avoid stumbling.
Physical interference associated with structures that comprise the horse’s stay mechanism(s) can sometimes precipitate stumbling. This is more prevalent in the hind limb (see chapter 18, p. 114).
Referred gait abnormalities.
An obligation to maintain diagonal synchrony and/or accommodate a dramatic shift in weight can cause the horse’s secondary limb to trip on occasion.
The act of faltering usually occurs due to an event that transpires at the time of foot breakover (fig. 12.2) and/or during limb flight. Horses that experience excessive tension or pain during maximum limb extension (just before breakover) and/or pain-mediated or biomechanical restriction during flexion (limb protraction) will be predisposed to stumbling. Both of these issues are accentuated by circumstances that delay breakover of the foot and/or increase the length of the stride (an excessively long toe, for example).
12.2 Foot Breakover
During ambulation, the horse’s hoof works like a lever with the toe acting as the pivot point. The term breakover refers to the action of the hoof as it pivots over the toe to lift and move the limb forward.
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