Equine hoof mechanics and function have been investigated for many years. One of the most reliable methods with which to assess hoof wall distortion is extensometry, a technique that uses electrical resistance strain gauges to identify changes in length of a given material (ie, a measurement of its deformation). In such circumstances, the forces acting on the surface of the material are translated into compressive (negative) or tensile (positive) strains.
Investigation of forelimb hoof wall strains in equids has led to the description of a pattern of deformation that is widely accepted. During stance, the front hoof wall is predominantly under compression. There is a palmar movement and flattening of the dorsal wall and flaring of the quarters, and the combination of these movements causes biaxial compression at the toe.1,a Compressive strains increase following impact and reach a peak close to midstance, before decreasing to the initial values. However, most of the information collected to date relates to horses that were walking and trotting at low speeds or, rarely, cantering slowly. There is little information as to how the front hoof responds to loading at high speeds,2 to our knowledge.
The relationship between equine hoof strains and shape has also been investigated and is not a simple issue. Various studies3–6 have revealed conflicting findings concerning the effect of TA on front hoof wall strains. Although results of a study3 indicated that strains decreased dorsally and increased laterally and medially with increasing TA, other investigations4,5 have provided data indicative of different effects. More recently, the redistribution of strains with unloading of the medial side at the expense of the lateral side of the front hoof with increasing TA at the trot has been proposed.6
Toe angle has been shown to decrease over time in exercising racehorses7 and warmbloods.8 In a study9 involving Standardbreds, TA increased following a period of mild trotting exercise, but that effect could not be related to exercise, given that similar changes were observed in nonexercised horses in the control group. These studies7–9 involved primarily the forelimb hooves of hoof-trimmed and shod horses, implying some degree of human-induced hoof changes. Toe angle changes in untrimmed unshod horses that undergo exercise have not been reported, to our knowledge. A decrease in the PHC of the forelimb hooves of racehorses in training has also been observed,10 but a pilot studyb investigating the same variable in the forelimb hooves of unshod horses exercised at various gaits on a treadmill failed to produce conclusive results.
The purpose of the study reported here was to investigate forelimb hoof wall strains and shape changes in unshod horses undergoing regular moderate exercise on a treadmill at selected speeds and gaits. The intent was to test the hypothesis that the pattern of deformation of the forelimb hoof wall during high-speed exercise would be the same as that found during low-speed exercise. Second, variation in TA and PHC in untrimmed unshod horses in response to a regular exercise regimen that included medium-rate galloping was investigated. Third, the effect of forelimb hoof shape changes on hoof wall strains was assessed to determine whether strains remained consistent in an individual horse despite a change in hoof shape.
Materials and Methods
Horses—Six horses of various body types were used in the study. The horses were between 3 and 17 years of age, and their weights ranged from 425 to 518 kg. There were 4 Thoroughbred geldings (height measured at the highest point of the shoulders [ie, withers], 150 to 179 cm), one 7-year-old Anglo-Arab gelding, and one 5-year-old Clydesdale-pony cross mare. The variation in body type, size, age, and breed was a deliberate measure to improve reproducibility,11 and hence reliability, of any outcome. Horses were housed in 7 × 15-m gravel yards throughout the experimental period and fed hay and pellets. Each horse was not shod, and the extent of hoof trimming was minimal (for removal of small pieces of broken hoof wall as necessary). All procedures used in the study were approved by the Faculty of Veterinary Science Animal Ethics Committee of the University of Melbourne.
Experimental procedures—For each horse, the hair around the coronet of each forelimb was clipped with a No. 40 blade prior to the beginning of the experiment. Taking the point of the frog as a reference, a line was drawn on the dorsal hoof wall with permanent ink to mark the toe and this line was maintained throughout the experiment.
Each horse underwent 12 exercise sessions on a treadmill during a period of 4 weeks; 3 exercise sessions were performed each week. Each exercise session comprised walking at 6 km/h (1.66 m/s) for 2 minutes, trotting at 15 km/h (4.16 m/s) for 4 minutes, and cantering at 30 km/h (8.33 m/s) for 4 (sessions 1 through 8) or 6 minutes (sessions 9 through 12); galloping at a medium rate (45 km/h [12.5 m/s]) for 2 minutes was included in sessions 1, 3, 6, 9, and 12 only.
Hoof strain measurements—For each horse, hoof strains for each forelimb were measured immediately before the first and immediately after the last exercise session. The 3 triaxial rosette strain gaugesc were attached midway down the left and the right forelimb hoof wall of each horse: 1 at the toe, 1 at the medial quarter, and 1 at the lateral quarter. The reference for the toe was the frontal axis of the limb, and the reference for the quarters was the widest point of the hoof.
The hoof wall surface where each gauge was placed was prepared by fine sanding and application of 70% alcohol. Gauges were attached with cyanoacrylate adhesive and kept in place by firm digital pressure and tape. The central element of each gauge was aligned with the long axis of the hoof wall tubules. To verify gauge alignment, close-up photographs of each gauge were obtained. Deviation from the tubular axis was estimated by image processing and analysis softwared as required.
Gauge strains were sampled with a portable signal conditionere strapped to the metacarpus and connected to the strain gauges. Care was taken to leave sufficient wire for free joint movement. Gauges were zeroed when each horse was standing square on the treadmill. The exercise session was started, and strains were sampled simultaneously in all channels at 40 Hz when the horse reached the desired speed at each gait; the duration of sample collection was the interval required to record a minimum of 7 strides. Digitally sampled analogue signals were sent to a portable computer with custom-made software.f The raw data of 7 strides at each gait were extracted from the recordings. Intervals containing 7 consecutive strides with consistent tracings were manually selected. Gauge strain values were corrected for zero, and the magnitude and angle of the principal strains were calculated. Angles were calculated with respect to the central element of the gauges and corrected for deviation from the tubular axis where necessary.
Hoof shape measurements—The left and the right forelimb PHC and TA were measured immediately before commencement of exercise sessions 1, 3, 6, 9, and 12 (sessions that included medium-rate galloping for 2 minutes). A flexible measuring tape placed around the coronet of each limb was used to assess PHC when the horse was standing as square as possible,10,b and measurements were read to the nearest 1.0 mm. The TA was measured with a hoof gauge7,g to the nearest 0.5° by use of the previously drawn line as a reference. Each measurement was obtained 3 times by the same operator (MCRB), with the tape or gauge removed and repositioned after each measurement and the horse repositioned as necessary. Mean values were calculated and used in the analysis.
Strain analysis—The boundaries for the stance phase of the stride12 were estimated from the tracings of the toe gauge on the basis of information published elsewhere.13,14 Delayed responses of the strains to loading were assumed. The beginning of the stance phase was standardized as the point at which strains began to increase, and the end of the stance phase was standardized as the point at which strains decreased to initial values; midstance was defined as the intermediate point. Seven strides at each gait were characterized according to the stance-phase components and aligned manually. Mean midstance and peak principal strains were calculated for the 7 strides and used in the analysis.
Statistical analysis—The shape measurement data were analyzed with software.h Paired t tests were performed to compare initial (exercise session 1) and final (exercise session 12) PHC and TA values for left and right forelimbs. The level of significance was set at 5% (P < 0.05) for this and all subsequent statistical analyses.
The strain data were analyzedi with a restricted maximum likelihood model with horse, limb, and site as random effects. The outcomes considered were ϵ2pk and ϵ2mid. The explanatory variables considered were limb, site, gait (implying different speeds), and week. All 2-way interactions were considered, but only the site-by-gait interaction was significant and was therefore the only one included in the final model. The overall tests for the explanatory variables were Wald tests, on the basis of the assumption of an underlying χ2 distribution. Comparisons of predicted means were performed. Of 288 observations, 60 were unavailable as a result of connection problems or gauge loss. This analysis assumes that the missing data were missing at random; therefore, no bias was expected to be introduced by the omission.
Results
Response to exercise—All horses tolerated the 4-week exercise protocol well. One horse developed slight lameness during week 3 and could not be galloped during exercise session 9. However, recovery was rapid; the horse was nonlame and complied with the remaining exercise sessions (sessions 10 through 12).
Hoof strain measurements—Minimum principal strain, corresponding to maximal compression, had the largest magnitude at all sites evaluated on the hoof wall at midstance. Minimum principal strain was also the peak strain observed during the stance phase of the stride. Therefore, the minimum principal strain component was the only strain considered for statistical analysis. A repetitive pattern was identified; compressive strains increased progressively after impact and reached peak values during the propulsive stage of the stance phase, either at midstance or closer to the end of the stance phase (Figure 1). Biaxial compression, in which maximum and minimum principal strains were both negative, was observed at the toe in 60% of the observations and was considered as an outcome.
Representative hoof strain profile at the toe for 1 stride of a forelimb of a horse during walking (A), trotting (B), cantering (C), and galloping at a medium rate (D) on a treadmill. Three triaxial rosette strain gauges were attached midway down the left and right forelimb hoof wall: 1 at the toe, 1 at the medial quarter, and 1 at the lateral quarter. Notice that the stance phase (represented by the portion of the tracing not equal to 0) is progressively shorter from the walk to the medium-rate gallop. Tracings obtained from the lateral and medial quarter gauges were similar.
Citation: American Journal of Veterinary Research 73, 11; 10.2460/ajvr.73.11.1735
Representative hoof strain profile at the toe for 1 stride of a forelimb of a horse during walking (A), trotting (B), cantering (C), and galloping at a medium rate (D) on a treadmill. Three triaxial rosette strain gauges were attached midway down the left and right forelimb hoof wall: 1 at the toe, 1 at the medial quarter, and 1 at the lateral quarter. Notice that the stance phase (represented by the portion of the tracing not equal to 0) is progressively shorter from the walk to the medium-rate gallop. Tracings obtained from the lateral and medial quarter gauges were similar.
Citation: American Journal of Veterinary Research 73, 11; 10.2460/ajvr.73.11.1735
Representative hoof strain profile at the toe for 1 stride of a forelimb of a horse during walking (A), trotting (B), cantering (C), and galloping at a medium rate (D) on a treadmill. Three triaxial rosette strain gauges were attached midway down the left and right forelimb hoof wall: 1 at the toe, 1 at the medial quarter, and 1 at the lateral quarter. Notice that the stance phase (represented by the portion of the tracing not equal to 0) is progressively shorter from the walk to the medium-rate gallop. Tracings obtained from the lateral and medial quarter gauges were similar.
Citation: American Journal of Veterinary Research 73, 11; 10.2460/ajvr.73.11.1735
The only significant interaction was site by gait, and this interaction was significant when either ϵ2mid (P < 0.001) or ϵ2pk (P < 0.001) was the outcome considered, except at the toe. There was no effect of week or limb on ϵ2mid or ϵ2pk (Table 1). Horses were allowed to canter and gallop on their preferred lead limb in the study, and equal numbers of lead and nonlead stances were captured at the canter and medium-rate gallop. In the few instances where we could compare lead limb versus nonlead limb canter and lead limb versus nonlead limb medium-rate gallop data in the same horse, no consistent trends were observed; hence, the effect of lead limb was not considered.
Mean ± SD ϵ2mid and ϵ2pk for the left and right forelimb hooves of 6 unshod horses before the first (baseline) and after the last (final) of 12 exercise sessions (involving walking, cantering, trotting, and galloping at a medium rate on a treadmill) during a 4-week period (3 exercise sessions/wk).
| Variable | ϵ2mid (μϵ) | P value | ϵ2pk(μϵ) | P value |
|---|---|---|---|---|
| Left limb | −1,708 ± 386.0 | 0.43 | −2,218 ± 433.3 | 0.54 |
| Right limb | −1,550 ± 385.8 | −2,085 ± 433.6 | ||
| Baseline | −1,624 ± 333.9 | 0.89 | −2,152 ± 377.2 | > 0.99 |
| Final | −1,635 ± 323.8 | −2,151 ± 368.2 |
Each horse underwent 12 exercise sessions on a treadmill during a period of 4 weeks; 3 exercise sessions were performed each week. Each exercise session comprised walking at 6 km/h (1.66 m/s) for 2 minutes, trotting at 15 km/h (4.16 m/s) for 4 minutes, and cantering at 30 km/h (8.33 m/s) for 4 (sessions 1 through 8) or 6 minutes (sessions 9 through 12); galloping at a medium rate (45 km/h [12.5 m/s]) for 2 minutes was included in sessions 1, 3, 6, 9, and 12 only. Data were collected by use of 3 triaxial rosette strain gauges that were attached midway down the left and right forelimb hoof wall: 1 at the toe, 1 at the medial quarter, and 1 at the lateral quarter. Data represent the mean of the baseline and final values for the right or left forelimb and the mean baseline and mean final values for both limbs. Some data were missing as a result of connection problems or gauge loss (left limb, n = 32; right limb, 28; baseline, 43; and final, 17).
μϵ = Microstrain.
Gait did not affect the midstance or peak strains at the toe (Tables 2 and 3). At the lateral quarter, both ϵ2mid and ϵ2pk increased significantly at the transition from a walk to a trot and at the transition from a canter to a medium-rate gallop but did not differ at the transition from a trot to a canter. At the medial quarter, midstance strains increased significantly from the walk to the trot and from the trot to the medium-rate gallop, but differences at the intermediate transitions from the trot to the canter or canter to the medium-rate gallop were not significant. A similar increase in peak strains between the walk and the medium-rate gallop occurred, with significant increases at the transitions up to the canter.
Mean ± SD ϵ2mid (μϵ) for the left and right forelimb hooves combined of 6 unshod horses recorded during walking, trotting, cantering, and galloping at a medium rate on a treadmill at each of 12 exercise sessions during a 4-week period (3 exercise sessions/wk).
| Gauge site | Gait | |||
|---|---|---|---|---|
| Walk | Trot | Canter | Medium-rate gallop | |
| Toe | −1,152 ± 490.9a,A | −1,350 ± 490.9a,A | −1,313 ± 505.6a,A | −1,285 ± 520.3a,A |
| Medial quarter | −893 ± 490.9a,A | −1,458 ± 490.9b,A | −1,710 ± 505.6b,c,A,B | −2,070 ± 520.3c,B |
| Lateral quarter | −1,141 ± 506.2a,A | −2,251 ± 506.2b,B | −2,071 ± 522.8b,B | −2,858 ± 536.4c,C |
The 3 triaxial rosette strain gauges used for data collection were attached midway down the left and the right forelimb hoof wall: 1 at the toe, 1 at the medial quarter, and 1 at the lateral quarter. Gauge strains were sampled with a portable signal conditioner strapped to the metacarpus and connected to the strain gauges. After gauges were zeroed when each horse was standing square on the treadmill, each exercise session was started, and strains were sampled simultaneously in all channels at 40 Hz when the horse reached the desired speed at each gait. The duration of sample collection was the interval required to record a minimum of 7 strides; intervals containing 7 consecutive strides with consistent tracings were selected for analysis.
Within each gait, site values with different capital superscript letters are significantly (P < 0.05) different.
Within each site, gait values with different lowercase superscript letters are significantly (P < 0.05) different. Some data were missing as a result of connection problems or gauge loss (toe–walk, n = 2; toe-trot, 2; toe–canter, 5; toe–gallop, 7; medial quarter–walk, 2; medial quarter–trot, 2; medial quarter–canter, 5; medial quarter–gallop, 7; lateral quarter–walk, 5; lateral quarter–trot, 5; lateral quarter–canter, 8; and lateral quarter–gallop, 10).
Mean ± SD ϵ2pk (μϵ) for the left and right forelimb hooves combined of 6 unshod horses recorded during walking, trotting, cantering, and galloping at a medium rate on a treadmill at each of 12 exercise sessions during a 4-week period (3 exercise sessions/wk).
| Gauge site | ||||
|---|---|---|---|---|
| Walk | Trot | Canter | Medium-rate gallop | |
| Toe | −1,842 ± 517.8a,B | −1,896 ± 517.8a,A | −2,053 ± 531.8a,A | −2,157 ± 546.0a,A |
| Medial quarter | −1,112 ± 517.8a,A | −1,807 ± 517.8b,A | −2,382 ± 531.8c,A | −2,606 ± 546.0c,A |
| Lateral quarter | −1,608 ± 554.6a,A,B | −2,561 ± 554.6b,B | −2,503 ± 572.7b,A | −3,292 ± 546.0c,B |
See Table 2 for key.
As the horses progressed from a walk to a medium-rate gallop, midstance strain differences between sites generally increased (Table 2). The greatest midstance strains were evident at the lateral quarter during the medium-rate gallop. Peak strains were less affected by site (Table 3).
Hoof shape measurements—The repeatability coefficients for left and right forelimb PHC and TA measurements were as follows: left PHC, 1.7 mm (95% CI, 1.3 to 2.7 mm); right PHC, 1.8 mm (95% CI, 1.3 to 2.7 mm); left TA, 1.4° (95% CI, 1.1° to 2.2°); and right TA, 1.0° (95% CI, 0.7° to 1.5°). There was a significant increase in TA during the 4-week exercise period (Table 4), but TA was not associated with midstance strains (P = 0.9) or peak strains (P = 0.75) when included as an explanatory variable in the statistical model. Proximal hoof circumference did not change from the initial to the final time period.
Mean ± SE values of PHC and TA for the left and right forelimb hooves of 6 unshod horses before the first (baseline) and after the last (final) of 12 exercise sessions (involving walking, cantering, trotting, and galloping at a medium rate on a treadmill) during a 4-week period (3 exercise sessions/wk).
| Variable | Left hoof | Right hoof | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Baseline | Final | Difference (final − baseline) | 95% CI | P value | Baseline | Final | Difference (final − baseline) | 95% CI | P value | |
| PHC (mm) | 366.2 ± 7.4 | 366.7 ± 6.8 | 0.5 ± 1.2 | −2.5 to 3.5 | 0.69 | 369.2 ± 6.4 | 369.8 ± (5.8) | 0.6 ± 1.1 | −2.1 to 3.3 | 0.59 |
| TA(°) | 53.2 ± 0.6 | 55.7 ± 0.7 | 2.5 + 0.5 | 1.2 to 3.8 | 0.004 | 52.8 ± 0.6 | 55.1 ± 0.8 | 2.5 ± 0.5 | 1.0 to 3.4 | 0.005 |
Forelimb PHCs and TAs were measured immediately before commencement of the exercise sessions that included galloping at a medium rate. A flexible measuring tape placed around the coronet of each limb was used to assess PHC when the horse was standing as square as possible. The TA of each limb was measured with a hoof gaugea to the nearest 0.5° (a line drawn on each dorsal hoof wall at the point of the frog was used as a reference). Each measurement was obtained 3 times by the same operator, and mean values calculated for inclusion in the analysis. For the comparison of baseline and final values for each variable, a value of P < 0.05 was considered significant.
Discussion
Results of the present study have confirmed that the previously described pattern of deformation of the equine forelimb hoof is maintained at higher speeds of locomotion. For the horses of the present study, the pattern of deformation was consistent among gaits, with strains increasing following impact and peaking in the propulsive stage of the stance phase. We had expected peak strains to occur at midstance,1,4 but in most instances, strains generally peaked slightly later in the stride, which might reflect differences in the boundaries set for the stance phase. A consistent spike indicating break over at the toe region has been described1,4 and should facilitate identification of the end of the stance phase. A similar spike was seldom identified in the data obtained in the study reported here, possibly because of different sampling rates among studies. However, despite possible differences in stride temporal characteristics, the pattern of deformation detected in the present study was in agreement with published data. As the stance phase progressed and more weight was imposed on the hoof wall, compression of the hoof material increased.
The predominance of compressive strains at all sites, with some evidence of biaxial compression at the toe and higher strains at the lateral quarter, in horses of the present study was in agreement with results of other studies and strongly suggests that the front hoof wall responds to loading in a similar manner, regardless of speed or differences in hoof shape, conformation, or body weight among horses. The horses used in the present study were deliberately selected to provide a nonhomogeneous group, particularly with regard to body type, yet hoof behavior was similar.
In the present study, the lack of a significant increase in strain at the forelimb toe associated with increasing speed was perhaps surprising. Ground reaction forces reflect loading and have been shown to relate to strain on the hoof wall.15 During locomotion, limb loading increases with increasing speed16 and an inverse relationship exists between duty factor and peak vertical force.17,18 It would then be reasonable to expect higher peak strain at least when cantering, compared with findings when trotting, not only because of the inferred greater speed, but also because of the characteristics of the gait, where 1 limb at a time is in contact with the ground. A horse's forelimb hooves typically land laterally19 and then load toward the toe and medial side; thus, the lack of a difference in the strain at the toe may reflect a redistribution of the load toward the quarters at the faster speeds. This was evidenced by the greater strain at the faster speeds in both the medial and lateral quarters of the forelimb hooves of the horses in the present study. However, compared with findings during cantering, the peak strain in the lateral quarter was significantly greater during medium-rate galloping but did not differ during trotting; conversely, the peak strain in the medial quarter was significantly greater during cantering than it was during trotting, but there was no difference between findings during medium-rate galloping and cantering. If the peak strain is a reflection of the limb loading and is affected by the pattern of hoof landing, with the highest strain presumably occurring at the time of greatest limb loading, then it appears that there is a difference in the pattern of hoof landing during cantering and galloping. Unfortunately, no independent data concerning hoof landing were collected in the present study.
Among the horses of the present study, the effect of gait was significant; however, the fact that the increase in strain was not always coincident with the increase in speed supports the idea of redistribution, rather than intensification, of strains with speed.6 This may also reflect the ability of the hoof material to become more stiff with loading, resulting in increased resistance to deformation during high-speed gaits.20
Strains were not significantly different between the left and the right forelimbs of the horses in the present study, suggesting that horses distribute loading evenly between the left and the right side of the body. This has in fact been demonstrated in horses trotting at different speeds.21 However, load distribution within the same hoof seems to be less even as indicated by the significant effect of site on midstance and peak strains, with higher strains on the lateral side of the hoof, detected in the study reported here. Asymmetric biomechanical behavior with higher strains on the lateral aspect of the hoof has been documented.22 Evidence that the medial side of the limb supports more weight has been reported elsewhere.23 Given the lateral location of the forelimb in relation to the center of a horse's body, more loading could be expected at the medial quarter and toe.24 Assuming that both sides of a hoof are morphologically similar and have similar elasticity,25,26 the higher strains observed on the lateral side of the horses' hooves in the present study suggest that different forces act on each side. However, medial and lateral angles also affect strains in the hoof wall, with decreasing compression as the angle increases, particularly at the lateral side.4 In the study reported here, the effect of medial and lateral angles could not be evaluated, given that these angles were not measured
An isolated effect of time (study week) on hoof wall strains was not expected, and time was indeed an unimportant term in this analysis. Our hypothesis was mainly that a period of regular exercise would induce hoof shape changes, which in turn would affect hoof wall strains. The small number of horses may account for some of the nonsignificant results of this study. However, the relationship between hoof shape and hoof wall strains is not clear at this stage. Strain distribution has been shown to differ among individual horses of similar age, body weight, and hoof shape that are housed under similar conditions,27 and an explanation for these differences is lacking.
Although hoof angle increased during the training period, the increase had no effect on hoof wall strains in the horses of the present study, contradicting the idea that more upright hooves undergo more strain.4 It could be argued that the small TA changes observed did not have the statistical power to demonstrate whether strains varied with TA or whether the effect of other variables may have interfered with the effect of TA.6 Results of a study28 on conformation of racing Thoroughbreds support the existence of nonindependent effects of hoof shape variables. Other factors to be considered are the exercise history and the individual stride characteristics of each horse, which might affect the stiffness of the hoof wall and hence its mechanical behavior.26 Unfortunately, detailed exercise history of the horses in the study reported here could not be obtained.
In a study9 involving Standardbreds, TA increased following a period of mild trotting exercise but similar changes were observed in nonexercised horses in the control group; the differences between groups were nonsignificant, suggesting exercise is not the only factor involved in TA changes of a horse's front hooves. Among other factors, exercise intensity may also have a role, given that TA decreases in racehorses during training.7 In those studies,7,9 the horses' feet were trimmed and shod and this may have influenced hoof shape and wear. The increase in TA observed in the horses of the present study cannot be related solely to exercise, given that other factors were not controlled, nor can it be a consequence of trimming and shoeing practices, given that no such interventions were performed on the horses' hooves during the experimental period. Our suggestion is that simple wear of the distal portion of the hoof wall during the 4-week exercise period led to the increase in TA in the study horses. The continuous growth of the hoof wall from the coronet29 implies the loss of a similar amount of material distally through wear, which results in maintenance of hoof size and shape in nature. Also, when not undergoing hoof care, healthy hooves may vary in shape over time.30
In the present study, changes in PHC reported for racehorses during training were not reproduced,10 but differences in exercise intensity and duration between studies make comparisons difficult (intensity and duration of the exercise protocol were limited by the fitness level of the horses and time constraints in the study reported here). However, on the basis of research data,b we had expected more consistent changes to occur. The results of the present study suggested either that PHC changes are a response to intense galloping only or that the measurement method was not sufficiently sensitive to detect subtle PHC changes. Despite having kept the coronet free of hair, we found it difficult to ensure placement of the measuring tape at the exact same position for each measurement, as reflected by the poor repeatability coefficients. Until a more precise method of measurement is available, small PHC changes should be interpreted with caution because confounding factors (eg, differences in positioning of the measuring tape and stance of the horse during data collections) cannot be avoided and may account for large differences in measurements obtained at the various time points.
Results of the present study have confirmed the existence of a consistent underlying pattern of deformation in the forelimb hoof wall of unshod horses undergoing moderate exercise; moreover, the pattern of deformation was not influenced by individual variations in hoof shape, body type, or body weight among horses. Strains in the equine forelimb hoof wall appeared to be dependent on site and gait but were not affected by discrete changes in TA. The PHC did not change in response to moderate regular exercise in unshod horses. The heterogeneous group of horses and missing data may have affected the significance of the study results, but the reliability of those results was increased because a heterogeneous group of horses was investigated. The limited number of horses in the study may explain some of the nonsignificant results obtained.
ABBREVIATIONS
| CI | Confidence interval |
| ϵ2pk | Minimum principal peak strain |
| ϵ2mid | Minimum principal midstance strain |
| PHC | Proximal hoof circumference |
| TA | Toe angle |
Leach DH. The structure and function of the equine hoof wall. PhD thesis, Department of Veterinary Anatomy, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada, 1980.
Lee CJL. Preliminary studies on factors influencing the hoof shape in horses. Master thesis, Faculty of Veterinary Science, University of Melbourne, Melbourne, VIC, Australia, 2008.
SA-09-060WR-120, Micro-Measurements, Raleigh, NC.
ImageJ, version 1.39u, National Institutes of Health, Bethesda, Md. Available at: rsbweb.nih.gov/ij/index.html. Accessed Sep 10, 2008.
CPE Systems Inc, Abbotsford, VIC, Australia.
Merritt JS. Mechanical modelling of the equine forelimb. PhD thesis, Faculty of Veterinary Science, University of Melbourne, Melbourne, VIC, Australia, 2007.
Ruidoso HG1, Sayers, Vernon Hills, Ill.
Stata, version 10.1, StataCorp, College Station, Tex.
Genstat, version 12.1, VSN International, Hemel Hempstead, Hertfordshire, England.
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