Page 1049 - Adams and Stashak's Lameness in Horses, 7th Edition

Occupational‐Related Lameness Conditions 1015

GAITED HORSES

VetBooks.ir david a. Wilson and Kevin G. KeeGan

EVALUATING GAITED HORSES FOR LAMENESS and hindlimb footfall synchrony. However, in gaited
breeds at speeds a little faster than a standard walk, they
Most horses in the United States move in four specific disassociate forelimb and hindlimb footfall. In gaited
gaits; walk, trot, canter, and gallop. The walk and trot breeds this faster disassociated gait may be faster than a
are symmetric gaits, and the canter and gallop are con­ trot in a non‐gaited horse. These faster than walking
sidered asymmetric gaits. Symmetric gaits are the easiest gaits have many different names, the flat walk, the run­
gaits to analyze for lameness because the earliest sign of ning walk, the rack, saddle gait … the list goes on and on.
lameness is gait asymmetry.
Lameness evaluation is more difficult in horses that
typically use a gait that is not a walk or trot. There are CLASSIFICATION OF GAITS
many other gaits used by horses, either naturally or
artificially by training, and these other gaits can be dif­ There are many ways to classify the various gaits of
ficult to evaluate without sufficient knowledge or expe­ the domestic horse. Gaits may be classified as:
rience. The trot is by far the most common symmetrical Stepping (walking) vs. leaping
gait, and the majority of horses in the United States are
evaluated for lameness at the trot. Therefore, most vet­ Symmetrical vs. asymmetrical
Two beat vs. four beat
erinarians are very comfortable evaluating horses at the
trot. There are both practical, meaning it is easier, and Lateral vs. diagonal sequence
Regular vs. lateral vs. diagonal couplet gaits
principled, meaning it is more accurate, reasons for
doing so. The trot has a large vertical suspension phase
that occurs twice during each stride, and that vertical Stepping (Walking) vs. Leaping Gaits
suspension phase exacerbates a weight‐bearing lame­ Stepping (walking) gaits lack an airborne (suspen­
ness because of the resulting effects on vertical ground
reaction force, which is the kinetic measure most highly sion) phase in the stride. Each limb is on the ground
4,10,17
Stance phases of
>50% of the total stride duration.
correlated with pain on weight bearing. The trot is
also a symmetric gait not only by side (left vs. right) the forelimb and hindlimb pairs overlap, with no period
of suspension and no high vertical displacement of the
but also by forelimb vs. hindlimb, which allows more
predictable effects on determination of compensatory body and no aerial phases of the stride. These are typi­
cally four‐beat gaits that have a lateral footfall sequence
lameness. All of these reasons make the trot easier and 20
better to evaluate for most veterinarians. of LH, LF, RH, RF.
By contrast, leaping gaits have at least one or usually
two aerial phases during each stride, when none of the
WHAT IS A GAITED HORSE? limbs are in contact with the ground. With leaping gaits,
primarily the trot and the pace, the concussion or ground
Technically all horses are gaited horses. A walk, trot, reaction forces on the limbs are usually greater than
and canter are “gaits.” However, horses are considered those horses using a stepping gait at equivalent speeds.
to be “gaited” if they perform a gait that is not a typical Therefore, this increased concussion in the leaping gaits
walk, trot, canter, or gallop. tends to exacerbate the differences in weight bearing
Gaited horses typically perform one of the many between limbs with pain and those without.
intermediate speed four‐beat gaits, which are collec­
tively referred to as ambling gaits. These horses are Symmetrical vs. Asymmetrical Gaits
selectively bred for their natural gaited tendencies and
8
are generally smooth to ride (Table 9.3). In most The rhythm or cadence of the right and left footfalls
“gaited” breeds, the ambling gait is a hereditary trait. defines gait symmetry. In symmetric gaits, the footfalls
The gene DMRT3 controls the spinal neurological cir­ of a pair of feet (forelimb pair or hindlimb pair) are
cuits related to limb movement and motion. 1,2,22 Even evenly spaced in time. 10,17 The forelimbs and hindlimbs
one copy of a premature stop codon mutation in the move symmetrically, but the left and right sides are 180°
DMRT3 gene (DMRT3:Ser301STOP), which diverged out of phase. 9,12 The movement of each pair of feet (fore
from a common ancestral sequence within the last or hind) is evenly spaced in time. The symmetric gaits
10,000 years, will produce gaitedness. However, some are distinguished from each other by the coordination
2
members of these breeds may not always gait, and some between the fore­ and hind limbs, the speed of progres­
naturally trotting breeds not listed in Table 9.3 may sion, the relative duration of stance and swing phases,
have ambling or “gaited” ability. and the presence/absence of aerial phases. 10
A gaited horse moves at a walk, similar to non‐gaited The trot and pace are at opposite ends of the spec­
horses. They place all four feet down independently. The trum considering symmetrical gaits, but they are the
change in foot placement occurs as the speed increases. closest to total symmetry such that the right and left and
Most horses begin to trot at faster speeds, with forelimb fore‐ and hindlimbs move in virtual symmetry. In other