The use of commercial HBs to protect the hooves of barefoot horses during trail riding and endurance riding has gained popularity in North America.1 Although various materials are used to manufacture HBs, most commercially available boots have a polyurethane sole, a silicone wedge pad, and an outer upper covering of woven fabric.a,b Hoof boots provide cushioning and protection of the sole. The main drawback of HBs is that the distance between the toe and heels (sole length) in contact with the ground is not adjustable; consequently, horses fitted with HBs have to adapt to the manufacturer's design.1 However, the effect of this enforced adaptation has not been critically evaluated, to our knowledge. The length of the hoof or shoe may impact the breakover time, which is defined as the period of rotation of the heels around the toe in the terminal part of the stance phase. The breakover time starts when the heels lift and the hoof begins to pivot at the toe and ends when the toe leaves the ground.2,3
Shoes with a toe extension can be used to treat flexural deformity of the distal interphalangeal joint in young horses or to prevent knuckling of the metacarpophalangeal joint during advancement of the limb in horses with loss of extension function due to extensor tendon lacerations.4–6 In young horses with flexural deformity of the distal interphalangeal joint, the goal is to increase the length of the deep digital flexor tendon to correct the distal interphalangeal joint deformity.7 The proposed mechanism of action of the shoes with a toe extension in horses with distal interphalangeal joint flexural deformity is through provision of increased length of the resistance arm from the distal interphalangeal joint, thereby requiring greater strain on the deep digital flexor tendon to initiate the breakover period.4 It is speculated that greater strain on the deep digital flexor tendon results in tendon elongation and correction of the deformity.7 This proposed mechanism is based on research findings that leaving the toes long and increasing the sole length in contact with the ground prolong the stance phase of the stride and increase the duration of the breakover period of the foot, thereby resulting in strain on the deep digital flexor tendon.2,8 However, the kinetic effects of shoes with a toe extension in healthy horses have not been investigated, to our knowledge.
In recent years, there has been an increased demand for horseshoes and protective devices for feet to allow horses to remain free of lameness.1 Horse owners and trainers have used HBs to maintain their horses’ bare feet and protect the hooves and soles during daily exercise.1 Also, some clinicians recommend the use of HBs for horses with hoof wall defects, signs of foot pain, solar puncture wound, or laminitis because the HBs provide sole support and shock absorption when the feet contact the ground, as well as the capability to elevate the heels, thereby relieving static tension on the deep digital flexor tendon during weight bearing.9,10 It is our clinical impression that HBs provide cushion support to the foot and decrease the vertical ground forces on the feet, which allow horses with acute or chronic signs of foot pain to be more comfortable while wearing the HBs. However, to our knowledge, the kinetic effects of the HBs in healthy, nonlame horses have not been investigated. We speculated that the use of HBs may alter the GRFs in nonlame horses during walking; therefore, investigating the locomotor forces during the stride may provide objective data to determine whether HBs have any effects on the GRFs of normal horses.
Force plate gait analysis is an objective method for measuring the reaction forces between the hoof and ground (ie, GRFs) and stance duration in nonlame and lame horses moving at different gaits.11–14 Furthermore, force plate data can also be used to determine the time at which peak GRF occurs, the impulses expressed as area under the force-time curve, and the point of application of the force (center of pressure) underneath each hoof.14 Force plate gait analysis is a reliable and repeatable means of assessing limb function, lameness, and the effect of different shoeing regimens in horses.15,16 The gait in horses can be affected by shoeing and by different types of shoe or hoof protective devices applied.4,17 The purpose of the present study was to investigate and compare the effects of popular commercially available HBs and shoes with a toe extension on the stance duration, GRF, and sole length in contact with the ground in nonlame horses during walking. It was hypothesized that in healthy horses during walking, application of HBs or toe-extension shoes would increase sole length in contact with the ground but would not modify the vertical or longitudinal (braking and propulsive) peak forces, compared with findings derived when the horses were barefoot.
Materials and Methods
Animals
Six Standardbreds (age range, 11 to 14 months; body mass range, 340 to 375 kg) were included in the study. There were 3 females and 3 males (all stallions), each of which was determined to be free of lameness (lameness grade 0 [on a 5-point scale]18) and to have symmetric hooves on the basis of findings of clinical lameness examinations performed by 2 equine clinicians. Lameness evaluations consisted of walking and trotting the horses on hard and soft ground in a straight line and in circles in both directions. Yearling Standardbreds were chosen for inclusion in the study because of their similar body conformation and tractable temperament. The study was reviewed and approved by the University of Illinois Institutional Animal Care Committee.
Experimental design
Seventy-two hours prior to the beginning of the study, the horses were walked daily for 30 minutes in both directions on a runway covered with a commercially available rubber (heavy-duty polyvinyl chloride closed cell foam; thickness, 1 cm) matc to accustom them to walking with an even rhythm and at a consistent speed (1.3 to 1.8 m/s) over the trial surface. Speed was measured by use of 5 infrared sensorsd placed 0.5 m apart; the sensors were connected to a computer. At the beginning of the study (day 0), horses had their 4 hooves trimmed and balanced by an experienced farrier so that, for each limb, the dorsal hoof wall was parallel with the proximal interphalangeal joint. Lateromedial radiographic views of both forelimb feet were obtained. The horses remained barefoot during a 48-hour adaptation period. After this period (day 2), the first force plate gait analysis session was performed with the horses barefoot. Immediately after data collection, the horses’ forelimbs were fitted with commercially available No. 7 HBsa (Figure 1) following the manufacturer's instructions. Hoof boots were made of urethane HB with a silicone padded wedged bottom. For each horse, lateromedial radiographic views of both forelimb feet with the applied HBs were obtained. The horses wore the HBs during a 48-hour adaptation period. After this period (day 4), a second force plate gait analysis session was performed with the horses fitted with the HBs. Immediately after data collection, the HBs were removed and the horses’ forelimbs were shod with an 8-mm-thick steel flat shoe and a 5-cm-long toe extension. For each horse, lateromedial radiographic views of both forelimb feet with the applied toe-extension shoes were obtained. The toe-extension shoes were composed of an 8-mm-diameter regular steel horseshoe with an iron extension (5 cm in length and 8 cm in width) welded to the dorsal aspect of the shoe.
Representative photographs of the forelimb of a young nonlame Standardbred that was fitted with a commercially available urethane HB with a silicone padded wedged bottom (A) and another forelimb fitted with a shoe that had a toe extension (B). The toe-extension shoe was created with an 8-mm-diameter regular steel horseshoe that had an iron extension (5 cm in length and 8 cm in width) welded to the dorsal aspect of the shoe.
Citation: American Journal of Veterinary Research 77, 5; 10.2460/ajvr.77.5.527
Representative photographs of the forelimb of a young nonlame Standardbred that was fitted with a commercially available urethane HB with a silicone padded wedged bottom (A) and another forelimb fitted with a shoe that had a toe extension (B). The toe-extension shoe was created with an 8-mm-diameter regular steel horseshoe that had an iron extension (5 cm in length and 8 cm in width) welded to the dorsal aspect of the shoe.
Citation: American Journal of Veterinary Research 77, 5; 10.2460/ajvr.77.5.527
Representative photographs of the forelimb of a young nonlame Standardbred that was fitted with a commercially available urethane HB with a silicone padded wedged bottom (A) and another forelimb fitted with a shoe that had a toe extension (B). The toe-extension shoe was created with an 8-mm-diameter regular steel horseshoe that had an iron extension (5 cm in length and 8 cm in width) welded to the dorsal aspect of the shoe.
Citation: American Journal of Veterinary Research 77, 5; 10.2460/ajvr.77.5.527
The horses remained shod with the toe-extension shoes during a 48-hour adaptation period. After this period (day 6), a third force plate gait analysis session was performed with the horses fitted with the toe-extension shoes. Immediately after data collection, the shoes were removed. The horses remained barefoot during a 48-hour adaptation period. After this period (day 8), a fourth force plate gait analysis session was performed with the horses barefoot (as in the first session). This fourth session was used as a control to verify that the HBs and the toe extension shoes had no secondary effects on the walking gait of horses.
Force plate gait analysis
The testing area was a 25-m-long runway covered with a rubber matc and a 60 × 120-cm force platee embedded in the center of the runway. One experienced handler walked all horses and allowed each horse to choose its own comfortable speed. Each data collection trial was considered valid when a walking speed (1.3 to 1.8 m/s) and acceleration or deceleration (0.15 m/s2) were achieved and only when the ipsilateral forelimbs and hind limbs fully contacted the force plate; walking speed was measured with the infrared sensors.d For each trial, the GRF data were sampled at 500 Hz and recorded with specialized softwaref that calculated the speed (m/s), stance time (seconds), vertical force to peak (N/kg), vertical impulse (N•s/kg), time of vertical force to peak (% stance), braking force peak (N/kg), braking force impulse (N•s/kg), time of braking force to peak (% stance), propulsive peak force (N/kg), propulsive force impulse (N•s/kg), and time of propulsive force to peak (% stance).
Only the kinetic variables from 5 valid trials were analyzed; for each set of 5 trials, the means of the variables for the left and right forelimbs were calculated as representative data for that limb of each horse. Asymmetry indices for stance time, vertical force to peak, and vertical impulse were calculated as the difference between the stance time, vertical force to peak, or vertical impulse of the left and right limbs divided by the sum of the stance time, vertical force to peak, or vertical impulse of the left and right limbs, respectively, and the results were expressed as a percentage as described by Weishaupt et al.19 These kinematic variables were selected because they are very sensitive indicators of forelimb lameness in horses.19 The transverse forces were also investigated in the present study but not reported because the values differed minimally between sessions and are generally negligible in lame horses.14
Symmetric stance time, vertical force to peak, or vertical impulse yields an asymmetry index equal to zero, whereas a higher peak force (or impulse or time) in either the left or right forelimb yields a positive or negative asymmetry index. In horses without lameness and symmetric interlimb timing, the stance time, vertical force to peak, and vertical impulse asymmetry indices have been reported to be < 3%.19
Subsequently, data for kinetic variables obtained from 5 valid trials generated by each pair of forelimbs were combined together and then averaged, and the mean values were used to compare the force plate gait analysis sessions. The GRF data were resolved into vertical and longitudinal (braking or propulsive) components, then normalized by the horse's body mass and reported as Newtons per kilogram. Impulse values of vertical and longitudinal forces (area under the force-to-time curves) were calculated by time integration of the curves, then normalized by the horse's body mass and reported as Newton-seconds per kilogram. In addition, total stance time (time elapsed from initial ground contact to liftoff) was expressed as seconds, and the individual time at which the reaction force peak amplitudes occurred (peak-time position) was expressed as a percentage of the stance phase duration.
Radiographic evaluation
Lateromedial radiographic views were obtained from both forelimb feet that were placed on wooden positioning blocks while each horse was bearing weight evenly on all 4 limbs at the following time points: when each horse was initially barefoot (day 0), fitted with the HBs (day 2), and shod with toe-extension shoes (day 4). The radiographic beam was always centered midway between the dorsal and palmar aspects of the coronary band at the same distance (0.75 m) from the foot. The sole length of each forelimb hoof (distance between the toe and heels of each hoof in contact with the wooden positioning block), sole length of the HB (distance between the toe and heels of each HB in contact with the wooden positioning block), and sole length of the toe-extended shoes (distance between the toe and heels of each shoe in contact with the wooden positioning block) were determined by measurement of the horizontal distance of the sole in contact with the wooden positioning block (Figure 2). These distances were measured 5 times for each limb by the same investigator (FNA), and the mean value was calculated. All measurements were obtained by use of the freehand line measurement tool of a DICOM (Digital Imaging and Communications in Medicine) workstation.g
Lateromedial radiographic views of the same forelimb of a horse without (A) and fitted with (B) an HB. The measurement obtained to determine the length of sole surface in contact with the ground or wooden positioning block is illustrated by the long dashed line in each image.
Citation: American Journal of Veterinary Research 77, 5; 10.2460/ajvr.77.5.527
Lateromedial radiographic views of the same forelimb of a horse without (A) and fitted with (B) an HB. The measurement obtained to determine the length of sole surface in contact with the ground or wooden positioning block is illustrated by the long dashed line in each image.
Citation: American Journal of Veterinary Research 77, 5; 10.2460/ajvr.77.5.527
Lateromedial radiographic views of the same forelimb of a horse without (A) and fitted with (B) an HB. The measurement obtained to determine the length of sole surface in contact with the ground or wooden positioning block is illustrated by the long dashed line in each image.
Citation: American Journal of Veterinary Research 77, 5; 10.2460/ajvr.77.5.527
Statistical analysis
The data were tested for normal distribution with a Shapiro-Wilk test. The data obtained from the force plate analyses had normal distributions; therefore, mean ± SD values of each variable and percentage duration of stance phase were determined by calculating the mean value of 5 trials of each forelimb. Statistical analysis used a mixed-model ANOVA for repeated measures accounting for the random effects of horse and fixed effects of session, time, and their interaction. Initial analyses included limb within horse as a random effect. For each variable of interest, an asymmetry index was calculated. The limb effect term and the aforementioned asymmetry indices were not significant, and the values for both forelimbs were averaged for the analyses. Statistical differences in stance time, vertical force to peak, vertical impulse, time of vertical force peak, braking force peak, braking force impulse, time of braking force peak, propulsive peak force, propulsive force impulse, and time of propulsive force peak among the 4 sessions were determined. Treatments were compared with a Tukey post hoc test of pairwise differences. Radiographic measurements had nonnormal distributions and were logarithmically transformed for analysis by means of a mixed-model ANOVA. For all analyses, statistical softwareh was used, and values of P ≤ 0.05 were considered significant.
Results
All horses remained free of lameness, completed all 4 force plate gait analysis sessions, and had a high degree of symmetry in stance time, vertical force to peak, and vertical impulse (Table 1). All the kinetic gait analysis results for both forelimbs were combined (Table 2). Although the walking speed achieved in each session was tightly controlled (1.3 to 1.8 m/s), the walking speed was slower for horses fitted with the HBs or shod with the toe-extension shoes than that for barefoot horses. The stance time was significantly (P < 0.01) increased when the horses were fitted with the HBs (7%) or shod with the toe-extension shoes (5%), compared with findings when horses were barefoot. Peak values of the GRF in the limbs were similar among sessions (Figure 3); however, the time of the braking force peak was significantly (P < 0.001) higher during the stance phase of the stride when horses were fitted with the HBs, compared with the time of the braking force peak during the other sessions. The values recorded when horses were barefoot before and after the use of HBs and toe-extension shoes were not significantly different. Radiographically, the sole length in contact with the ground when horses wore HBs or toe-extension shoes (14.3 and 17.6 cm, respectively) was significantly (P < 0.001) longer than the sole length in contact with the ground when horses were barefoot (12.7 cm).
Representative vertical (A) and longitudinal (B) forelimb force-stance time curves obtained from 1 of the 6 nonlame horses used to determine and compare the effect of HBs and shoes with a toe extension on forelimb stance duration, GRF, and sole length in contact with the ground during walking. Force plate analysis for each horse was performed on a 25-m-long runway covered with a rubber mat and a 60 × 120-cm force platee embedded in the center of the runway. Walking speed (1.3 to 1.8 m/s) was measured by use of 5 infrared sensorsd placed 0.5 m apart; the sensors were connected to a computer. The force plate analysis data were generated when the horse was barefoot (blue line), fitted with HBs (yellow line), or shod with toe-extension shoes (red line). The forces are expressed in Newtons per kilogram of body mass. For this horse and all others, the vertical forces had 2 peaks; the second peak was always consistently higher than the first. Notice that when the horse was fitted with the HBs or shod with toe-extension shoes, there was less decelerative effort (negative portion of the curve) and more accelerative effort (positive portion of the curve), compared with the more evenly distributed findings when the horse was barefoot.
Citation: American Journal of Veterinary Research 77, 5; 10.2460/ajvr.77.5.527
Representative vertical (A) and longitudinal (B) forelimb force-stance time curves obtained from 1 of the 6 nonlame horses used to determine and compare the effect of HBs and shoes with a toe extension on forelimb stance duration, GRF, and sole length in contact with the ground during walking. Force plate analysis for each horse was performed on a 25-m-long runway covered with a rubber mat and a 60 × 120-cm force platee embedded in the center of the runway. Walking speed (1.3 to 1.8 m/s) was measured by use of 5 infrared sensorsd placed 0.5 m apart; the sensors were connected to a computer. The force plate analysis data were generated when the horse was barefoot (blue line), fitted with HBs (yellow line), or shod with toe-extension shoes (red line). The forces are expressed in Newtons per kilogram of body mass. For this horse and all others, the vertical forces had 2 peaks; the second peak was always consistently higher than the first. Notice that when the horse was fitted with the HBs or shod with toe-extension shoes, there was less decelerative effort (negative portion of the curve) and more accelerative effort (positive portion of the curve), compared with the more evenly distributed findings when the horse was barefoot.
Citation: American Journal of Veterinary Research 77, 5; 10.2460/ajvr.77.5.527
Representative vertical (A) and longitudinal (B) forelimb force-stance time curves obtained from 1 of the 6 nonlame horses used to determine and compare the effect of HBs and shoes with a toe extension on forelimb stance duration, GRF, and sole length in contact with the ground during walking. Force plate analysis for each horse was performed on a 25-m-long runway covered with a rubber mat and a 60 × 120-cm force platee embedded in the center of the runway. Walking speed (1.3 to 1.8 m/s) was measured by use of 5 infrared sensorsd placed 0.5 m apart; the sensors were connected to a computer. The force plate analysis data were generated when the horse was barefoot (blue line), fitted with HBs (yellow line), or shod with toe-extension shoes (red line). The forces are expressed in Newtons per kilogram of body mass. For this horse and all others, the vertical forces had 2 peaks; the second peak was always consistently higher than the first. Notice that when the horse was fitted with the HBs or shod with toe-extension shoes, there was less decelerative effort (negative portion of the curve) and more accelerative effort (positive portion of the curve), compared with the more evenly distributed findings when the horse was barefoot.
Citation: American Journal of Veterinary Research 77, 5; 10.2460/ajvr.77.5.527
Mean ± SD left and right forelimb kinetic gait variables during walking derived from force plate analysis data obtained from 6 young nonlame horses during 180 force plate trials (30 trials/horse) performed when the horses were barefoot, fitted with commercially available HBs, or shod with toe-extension shoes (10 trials/condition).
| Condition | Variable | Left forelimb | Right forelimb | Asymmetry index (%) |
|---|---|---|---|---|
| Barefoot | Stance (s) | 0.74 ± 0.08 | 0.72 ± 0.09 | 1.85 ± 0.10 |
| Vertical force peak (N/kg) | 6.74 ± 0.48 | 6.75 ± 0.58 | −0.68 ± 0.53 | |
| Vertical impulse (N•s/kg) | 3.31 ± 0.39 | 3.33 ± 0.32 | −1.38 ± 0.78 | |
| HBs | Stance (s) | 0.78 ± 0.06 | 0.79 ± 0.07 | −2.02 ± 0.6 |
| Vertical force peak (N/kg) | 6.48 ± 0.46 | 6.54 ± 0.49 | −0.86 ± 0.84 | |
| Vertical impulse (N•s/kg) | 3.41 ± 0.36 | 3.42 ± 0.27 | −1.02 ± 0.56 | |
| Toe-extension shoes | Stance (s) | 0.77 ± 0.06 | 0.77 ± 0.02 | 1.05 ± 0.08 |
| Vertical force peak (N/kg) | 6.65 ± 0.24 | 6.62 ± 0.30 | 0.17 ± 0.4 | |
| Vertical impulse (N•s/kg) | 3.36 ± 0.32 | 3.40 ± 0.52 | −1.33 ± 0.88 |
At the beginning of the study (day 0), horses had their 4 hooves trimmed and balanced so that, for each limb, the dorsal hoof wall was parallel with the proximal interphalangeal joint. The horses remained barefoot during a 48-hour adaptation period. After this period (on day 2), the first force plate gait analysis session was performed with the horses barefoot. Immediately after data collection, the horses’ forelimbs were fitted with commercially available HBs following the manufacturer's instructions. Hoof boots were made of urethane with a silicone padded wedged bottom. The horses wore the HBs during a 48-hour adaptation period. After this period (on day 4), a second force plate gait analysis session was performed with the horses fitted with the HBs. Immediately after data collection, the HBs were removed and the horses’ forelimbs were shod with a toe-extension shoe. The toe-extension shoes were composed of an 8-mm-diameter regular steel horseshoe with an iron extension (5 cm in length and 8 cm in width) welded to the dorsal aspect of the shoe. The horses remained shod with the toe-extension shoes during a 48-hour adaptation period. After this period (on day 6), a third force plate gait analysis session was performed with the horses fitted with the toe-extension shoes. Immediately after data collection, the shoes were removed. The horses remained barefoot during a 48-hour adaptation period. After this period (on day 8), a fourth force plate gait analysis session was performed with the horses barefoot (as in the first session). Force plate analysis for each horse was performed on a 25-m-long runway covered with a rubber mat and a 60 × 120-cm force platee embedded in the center of the runway. Walking speed (1.3 to 1.8 m/s) was measured by use of 5 infrared sensorsd placed 0.5 m apart; the sensors were connected to a computer. Kinetic gait analysis was performed at a walk for 5 valid trials at various time points, and the data obtained from each forelimb were analyzed and reported separately. An asymmetry index was calculated as the difference between the stance time, vertical force to peak, or vertical impulse of the left and right limbs divided by the sum of the stance time, vertical force to peak, or vertical impulse of the left and right limbs, respectively, and the results were expressed as a percentage. Symmetric stance time, vertical force to peak, or vertical impulse yields an asymmetry index equal to zero, whereas a higher peak force (or impulse or time) in either the left or right forelimb yields a positive or negative asymmetry index. Barefoot data shown are from the first force plate analyses.
Mean ± SD combined forelimb kinetic gait variables during walking derived from force plate analysis data obtained from 6 young nonlame horses during 180 force plate trials (30 trials/horse) performed when the horses were barefoot, fitted with commercially available HBs, or shod with toe-extension shoes (10 trials/condition).
| Variable | Barefoot (baseline) | HBs | Toe-extension shoes |
|---|---|---|---|
| Speed (m/s) | 1.62 ± 0.22 | 1.46 ± 0.31 | 1.50 ± 0.10 |
| Stance time (s) | 0.73 ± 0.08a,b | 0.78 ± 0.07a | 0.77 ± 0.08b |
| Vertical force peak (N/kg) | 6.74 ± 0.66 | 6.51 ± 0.65 | 6.63 ± 0.34 |
| Vertical impulse (N•s/kg) | 3.31 ± 0.46 | 3.42 ± 0.34 | 3.38 ± 0.34 |
| Time of vertical force peak (% stance) | 62.00 ± 4.20 | 63.00 ± 4.10 | 60.00 ± 4.40 |
| Braking force peak (N/kg) | −0.95 ± 0.18 | −0.91 ± 0.18 | −0.93 ± 0.20 |
| Braking force impulse (N•s/kg) | −0.17 ± 0.05 | −0.17 ± 0.04 | −0.17 ± 0.05 |
| Time of braking force peak (% stance) | 13.0 ± 3.5a | 16.0 ± 4.1a,b | 13.0 ± 3.9b |
| Propulsive peak force (N/kg) | 0.95 ± 0.20 | 1.02 ± 0.20 | 0.95 ± 0.17 |
| Propulsive force impulse (N•s/kg) | 0.18 ± 0.05 | 0.21 ± 0.05 | 0.20 ± 0.05 |
| Time of propulsive force peak (% stance) | 74.0 ± 4.9 | 75.0 ± 4.0 | 73.0 ± 4.7 |
The values for horses when they were barefoot before and after the application of HBs and subsequently toe-extension shoes were not significantly different; thus, data obtained when the horses were barefoot after the use of toe-extension shoes are not shown.
Within a row, values with the same superscript letters are significantly (P < 0.05) different.
See Table 1 for key.
Discussion
The study of this report was carried out to investigate the effect of a popular brand of HB (available at the time) on GRF and sole length of the HB in contact with the ground in young Standardbreds. Most commercially available HBs are used for hoof protection, although some horse trainers and owners currently use them for barefoot horses to protect the hooves and soles from wear during routine training or trail rides. In our hospital, the HBs are commonly used for horses with sore feet while they are kept in stalls or being walked; thus, the present study was restricted to the analysis of locomotion forces during walking. The results of this study indicated that there was no significant modification of the vertical and longitudinal (braking and propulsive) forces when young healthy horses were fitted with HBs. The transverse forces were also investigated in the present study but not reported because the values differed minimally between sessions and are generally negligible in lame horses.14 It is possible that vertical and longitudinal forces in the forelimbs when horses were fitted with HBs would be different at a gait faster than a walk because the peak vertical GFR is smaller during walking than during faster gaits.11–13 However, additional work is required to determine whether larger modifications of the GRF in horses fitted with HBs exist at a faster gait.
In the present study, when the horses were fitted with HBs or shod with shoes with a toe extension, the stance durations were prolonged (compared with findings when horses were barefoot), which was likely a result of a decreased speed recorded during those sessions because the stance duration is negatively correlated with walking speed.20,21 We speculate that when fitted with HBs or shod with toe-extension shoes, the horses had a longer stance phase and walked at a lower speed because of increased locomotion action secondary to shoeing and increased weight on the distal portion of the limb, given that these horses were not adapted to wearing horseshoes or HBs.4,22 Unfortunately, the kinematic (temporal, linear, and angular characteristics of the stride) effect of HBs or toe-extension shoes, including breakover time, could not be investigated because this type of analysis was not available during the study period. Therefore, data from future investigations on the kinematic effect of the HBs or shoes with a toe extension may complement the results of the present study.
On first contact of a foot with the ground, impact energy is generated and dissipated through the foot and the remainder of the limb as the foot interacts with the surface.15 This energy is affected by several factors including gait, speed, surface, and the use of horseshoes.4 During contact of the hoof with the force plate, the recorded longitudinal (braking and propulsive) forces represent deceleration and acceleration during the stance phase of the stride.14 The time for braking force to peak was prolonged only when horses were fitted with the HBs, which is consistent with a slower deceleration phase during the initial impact of the limb with the ground.14
The present study had some limitations. First, the study included 6 young horses; therefore, the study results may not apply to adult horses that are more routinely fitted with HBs; however, our clinical experience regarding the use of HBs in adult horses suggests that the results of the present study are relevant to adult horses. Additional work is required to determine whether larger modifications of the GRF in adult horses fitted with HBs exist. Second, the present study was conducted with a prospective, observational, single crossover study design. The conditions were not randomized; nonetheless, the kinetic gait analysis results at the beginning and end of the study were similar. The experimental approach was chosen to facilitate execution of the study and determine whether a carry over effect existed. The study findings indicated the use of HBs and shoes with a toe extension similarly prolonged the stance time of nonlame horses during walking, although the locomotor forces during walking did not change significantly. Also, the use of HBs prolonged the deceleration phase of the stride and increased the length of sole in contact with the ground in the study horses.
Acknowledgments
Supported by the Department of Clinical Veterinary Medicine, College of Veterinary Medicine, University of Illinois.
ABBREVIATIONS
| GRF | Ground reaction force |
| HB | Hoof boot |
Footnotes
Soft-Ride Equine Comfort Boots, Soft-Ride Corp, Vermilion, Ohio.
Easyboot Rx, EasyCare, Tucson, Ariz.
Anti-Fatigue Mat, 9RHZ4, Grainger, Palatine, Ill.
Infrared photoelectric sensor, MEK-92-PAD, Mekontrol Inc, Northborough, Mass.
Force plate, EQ6001200–4000, AMTI Inc, Watertown, Mass.
Acquire, version 7.33, Sharon Software Inc, Owosoo, Mich.
Kodak Carestream Pacs, version 11.3, Carestream Health, Rochester, NY.
PROC MIXED, SAS, version 9.3 for Windows, SAS Institute Inc, Cary, NC.
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