Functional locomotor consequences of
uneven forefeet for the trot of individual
riding horses
Nathan Wiggers
Student number: 3260267
October 2013
Supervisors:
Dr. S. Nauwelaerts
Dr. S.J. Hobbs
Dr. W. Back
i
Dr. C.F. Wolschrijn
Abstract
Reasons for performing study:
It has been generally accepted that a symmetrical distal limb conformation is an important
prerequisite for a successful performance, as it has often been hypothesized that uneven feet should
be considered as an important enhancing factor for the development of lameness. On a population
level it has been demonstrated already that uneven footed horses seemingly are retired earlier from
competition, but the biomechanical consequences for an individual horse are not known yet.
Objectives:
To provide a better definition of uneven feet using objective quantifiable variables, to evaluate the
functional (a)symmetries of horses with even and uneven feet, and to evaluate the functional
differences between feet categorized as flat, medium or upright.
Methods:
Eight anatomical parameters that quantified conformational differences in the distal forelimbs of
horses with a varied range of hoof asymmetries (n=36, of which 2 were lame at trot) were compared
using discriminant analysis. Kinetics and distal limb kinematics of the clinically non-lame horses were
collected at trot and compared between even versus uneven forefeet and between flat, medium and
upright feet using MANOVA followed by ANOVA. The relative influence of differences in hoof angle
between the forefeet and of absolute hoof angle on functional parameters was analyzed by multiple
regression analysis.
Results:
It appeared that unevenness was best determined by the absolute differences in dorsal hoof angle
between the forefeet. In horses with uneven feet, the flatter foot showed a significantly larger
maximal horizontal braking and vertical ground reaction force, a larger vertical fetlock displacement
and a less stiff limb spring. A steeper hoof angle was linearly correlated with an earlier brakingpropulsion transition. No significant differences were found between feet categorized as flat,
medium or upright.
Conclusion and potential relevance:
The conformational differences between the forefeet were more important for loading
characteristics than the individual foot conformation. The recorded differences in vertical force
between the uneven forefeet could in fact imply an early, subclinical sign of lameness developing in
the steeper forefoot, as these kinetic differences yet appeared even smaller than those reported for
a subtle lameness when becoming clinically evident.
ii
Table of Contents
Abstract ....................................................................................................................................................ii
Table of Contents ....................................................................................................................................iii
List of Abbreviations .................................................................................................................................v
1.
Introduction ..................................................................................................................................... 1
2.
Materials and methods ................................................................................................................... 4
2.1
Horses ...................................................................................................................................... 4
2.2
Measurement systems and data collection ............................................................................ 5
2.3
Data processing and analysis................................................................................................... 7
2.3.1
Definition of uneven feet based on objective quantifiable variables ............................. 7
2.3.2
Functional parameters .................................................................................................... 9
2.4
3.
Statistical analysis .................................................................................................................. 11
2.4.1
Definition of uneven feet based on objective quantifiable variables ........................... 11
2.4.2
Relationship between unevenness and functional parameters.................................... 11
2.4.3
Relationship between individual foot conformation and functional parameters ........ 12
2.4.4
Relative weight of conformational differences between the forefeet and of individual
foot conformation ......................................................................................................... 12
Results ........................................................................................................................................... 13
3.1
Definition of uneven feet based on objective quantifiable variables ................................... 13
3.2
Foot classification .................................................................................................................. 15
3.3
Relationship between unevenness and functional parameters............................................ 16
3.3.1
Longitudinal ground reaction force ............................................................................... 16
3.3.2
Vertical ground reaction force ...................................................................................... 18
3.3.3
Resultant vertical-longitudinal ground reaction force .................................................. 19
3.3.4
Force-displacement curve ............................................................................................. 20
3.4
Relationship between individual foot conformation and functional parameters ................ 21
3.5 Relative weight of conformational differences between the forefeet and of individual foot
conformation ............................................................................................................................ 22
iii
4.
Discussion ...................................................................................................................................... 23
4.1
Definition of uneven feet based on objective quantifiable variables ................................... 23
4.2
Relationship between unevenness and functional parameters............................................ 26
4.2.1
Longitudinal ground reaction force ............................................................................... 26
4.2.2
Vertical ground reaction force ...................................................................................... 27
4.2.3
Stiffness ......................................................................................................................... 28
4.3
Relationship between individual foot conformation and functional parameters ................ 30
4.4
Conclusion ............................................................................................................................. 31
4.5
Limitations and recommendations for future research ........................................................ 32
Acknowledgements ............................................................................................................................... 33
References ............................................................................................................................................. 34
iv
List of Abbreviations
AAEP
American Association of Equine Practitioners
Angle Frmax
angle of resultant ground reaction force vector
DF
discriminant function
Fetzmax
maximal vertical displacement of the fetlock joint
Frmax
peak resultant vertical-longitudinal ground reaction force
Fx
longitudinal ground reaction force
Fx at Frmax
longitudinal force at the time point of peak resultant ground reaction force
Fxmax
peak propulsive ground reaction force
Fxmin
peak braking ground reaction force
Fz
vertical ground reaction force
Fz at Fetzmax
vertical force at maximal vertical fetlock displacement
Fz at Frmax
vertical force at the time point of peak resultant ground reaction force
Fzmax
peak vertical ground reaction force
GRF
ground reaction force
HHA
highest hoof angle
JFxneg
total braking impulse
JFxpos
total propulsive impulse
JFz
total vertical impulse
LHA
lowest hoof angle
MC3
third metacarpal bone
Pprox
proximal phalangeal bone
tFrmax
time to reach the peak resultant ground reaction force
tFxmax
time to reach the peak propulsive ground reaction force
tFxmin
time to reach the peak braking ground reaction force
tFxzero
time to reach the moment of transition from a braking to a propulsive force
tFzmax
time to reach the peak vertical ground reaction force
VC
visual classification
v
1. Introduction
It has been generally accepted that there is a relationship between conformation of the limb and
predisposition to lameness (Anderson et al., 2004; Balch et al., 1995; Kane et al., 1998; Ross and
Dyson, 2003; Stashak et al., 2002). Distal limb injuries seem to lead to early retirement of horses used
for competition (Kaneene et al., 1997; Wallin et al., 2000; Wallin et al., 2001). Not surprisingly, horses
with a poor limb conformation are rejected at studbook selections.
A normal forefoot has a hoof angle between 50° and 55°. The angle of the heel and the dorsal hoof
wall angle should be comparable to each other. Furthermore, the dorsal hoof wall and the dorsal
surface of pastern (the hoof-pastern axis) should be parallel (Stashak et al., 2002). A commonly seen
undesirable aspect of distal limb conformation is unevenness, i.e. two forefeet that differ in shape,
size and hoof angle (van Heel et al., 2006a).
Etiology and clinical significance of uneven feet
The cause of uneven feet can be found in lateralized behavior of grazing foals (van Heel et al.,
2006a). Compared with mature horses, foals have a large limb length relative to the height of the
trunk (Keeling and Gonyou, 2001). Consequently, foals are forced to spread the limbs while grazing. A
systematic preference for positioning the legs while grazing can lead to development of uneven feet,
with the retracted hoof becoming the more upright hoof. Long-legged horses with a small head are
more prone to develop lateralized behavior and uneven feet (van Heel et al., 2006a).
In adult horses, it is believed that uneven feet could be caused by (distal limb) pain. Pain in the distal
limb could lead to unloading and retraction of the limb and, consequently to the development of a
more upright hoof (Bakker et al., 2012; van Heel et al., 2006a).
The clinical significance of uneven feet is still unclear, but it has often been hypothesized that uneven
feet should be considered as an important enhancing factor for the development of lameness. In a
study of Bakker et al. (2012) on lame uneven footed horses, 60% of the horses showed a lameness in
the upright foot, while 40% of the horses was lame in the flat foot. Radiographs of these horses
demonstrated that the upright foot had a more radiolucent (osteoporotic) navicular bone with a
more pronounced (remodeled) dorsal flexor side and a more radiodens (compact) deep digital flexor
tendon. However, uneven feet and lameness may affect one another and exact details about their
interaction are still lacking.
Besides lameness, there is a relationship between unevenness and performance. On a population
level it has been demonstrated that uneven footed horses are retired earlier from competition at
elite level showjumping (Ducro et al., 2009b). Moreover, a study of van Heel et al. (2010) revealed a
side preference for transitions from trot to canter in horses with uneven feet.
1
Quantification of uneven feet
In a clinical setting, uneven feet are often judged visually which is a rather subjective method. For
experimental purposes, unevenness of the feet has been mostly determined by absolute difference
in hoof angle, based on measurements on standardized photographs. In previous studies, horses with
a relative intra-individual difference in hoof angle above the mean of the investigated population
were classified as uneven (Kroekenstoel et al., 2006; Moleman et al., 2006; van Heel et al., 2006a;
van Heel et al., 2010). A classification solely based on difference in hoof angle could be too simple as
uneven feet might have other differences in size and shape too. Ducro et al. (2009a) found that high
heels are related to a narrow hoof shape and a steep pastern angle. They suggested that studbook
judges might focus mainly on the presence of a narrow hoof with high heels and a steep pastern.
Wilson et al. (2009) demonstrated that hoof spread (i.e. the difference between hoof width at the
bottom and top of the hoof) was significantly associated to fetlock height, third metacarpal length
and elbow height. Apparently, assessing unevenness is a complex process based on multiple aspects.
This raises the following question: how can uneven feet be defined using objective quantifiable
variables?
Functional consequences of foot conformation
Previous studies have demonstrated that a difference in hoof angle between the forefeet is related
to a difference in loading of the feet while standing still (Kroekenstoel et al., 2006; Moleman et al.,
2006; van Heel et al., 2006a). Uneven footed foals showed a more palmar located center of pressure
in the flatter hoof compared to the upright hoof at age 55 weeks (van Heel et al., 2006a) and the
flatter foot showed a larger lever arm of the proximal and distal interphalangeal joints at age 27 and
55 weeks (Kroekenstoel et al., 2006). In mature horses, the moment on the distal interphalangeal
joint of the flat foot increased more during an 8 week shoeing interval than that of the upright foot
(Moleman et al., 2006).
While most studies on uneven feet were mainly focused on horses while standing still (as described
above), little is known about the functional consequences of uneven feet during locomotion.
However, the influence of artificially induced changes in hoof angle on kinetics and kinematics has
been studied more extensively.
Clayton (1990) demonstrated a prolonged breakover time in flat hooves trimmed with a long toe. It
might take longer for the center of mass to rotate over a flat footed limb, which could lead to a later
onset of breakover and a later transition from horizontal braking to propulsive forces. For the vertical
ground reaction forces, no differences in peak forces at trot were found after the application of a 6°
heel wedge (Willemen et al., 1999).
Results from previous studies on the maximal extension of the fetlock joint after the application of a
heel wedge were conflicting. Some studies found no significant effect after application of a 6° degree
heel wedge at trot (Chateau et al., 2006; Willemen et al., 1999), whereas others found a significant
reduction in maximal fetlock extension at trot after heel elevation with a 5° wedge (Scheffer and
Back, 2001). From clinical observations it has been suggested that horses with uneven feet show a
2
reduced fetlock extension in the upright footed forelimb, especially detectable at the walk, often
leading to a 1/5 AAEP lameness score (pers. observ. Wim Back).
Earlier research has demonstrated that stance duration is relatively independent of changes in foot
conformation (Chateau et al., 2004; Chateau et al., 2006; Clayton, 1990; van Heel et al., 2006b;
Wilson et al., 1998). Furthermore, van Heel et al. (2006b) showed that horses compensate for
changes in hoof morphology during a shoeing interval by changes in joint angles of the distal limb,
rather than by changes in timing variables.
Since most of the above-mentioned studies evaluated the influence of (artificially induced) changes
in hoof angle, rather than of conformational differences between the forefeet, it is difficult to
extrapolate their results to horses with uneven feet. To investigate the functional consequences of
uneven feet during locomotion, two approaches can be performed. The first approach focuses on the
conformational differences between the forefeet and attempts to answer the question: what are the
differences between the functional (a)symmetries of horses with even and uneven feet? The second
approach focuses on the consequences of the conformation of the individual foot and answers the
question: what are the functional differences between feet categorized as flat, medium or upright?
Hypotheses
For a better understanding of the mechanism and consequences of uneven feet, the objective of this
study was to test the following hypotheses:
 Horses with uneven feet are expected to have larger differences in key anatomical variables
between the forefeet than horses with even feet.
 Functional biomechanical parameters at the trot are associated with the conformation of the
individual foot as well as with the differences in conformation between the forefeet.
 In horses with uneven feet, the breakover occurs later in the flatter foot compared to the steeper
foot. This is expected to be associated with a later transition from braking to propulsion in the
fore-aft forces and with an altered pattern of the longitudinal force profile. In both even and
uneven footed horses, the vertical forces are not significantly different between the forefeet. The
same is hypothesized for the timing of the force peaks and the stance duration. In uneven footed
horses, the flatter foot is expected to show more vertical displacement of the fetlock joint while
vertical forces do not differ between the feet, leading to a less stiff limb spring in the flatter foot.
For horses with even feet, it is expected that functional parameters do not differ between the
forefeet.
 It is hypothesized that feet categorized as flat, medium or upright have their own biomechanical
characteristics at the trot. Compared to medium feet, the transition from longitudinal braking to
propulsive forces occurs earlier in upright feet, while flat feet will show a later transition. Vertical
forces and the timing of the force peaks do not differ between foot categories. Compared to
medium feet, upright feet are expected to show less vertical displacement of the fetlock joint
and a stiffer limb spring.
3
2. Materials and methods
2.1 Horses
Thirty-six riding horses of different breeds with visually detectable even (n = 13) or uneven (n = 23)
feet were studied (tables 2.1 and 2.2). Mean ± s.d. weight was 557 ± 77 kg and mean ± s.d. age was
12 ± 5 years. Two of these horses showed a forelimb lameness at trot, with American Association of
Equine Practitioners (AAEP) lameness scores of 1/5. Eight horses showed a 1/5 forelimb lameness at
walk but were sound at trot.
Table 2.1 – Breeds, numbers, age and weight of horses used in the study
Breed
N
Mean ± s.d age (years)
Mean ± s.d weight (kg)
Dutch Warmblood horse (KWPN)
Dutch Ridinghorse and Pony Studbook (NRPS)
Arabian horse
Friesian horse
Fjord
Thoroughbred
Haflinger
New Forest pony
28
1
2
1
1
1
1
1
12 ± 6
5±0
11 ± 1
10 ± 0
9±0
19 ± 0
10 ± 0
9±0
581 ± 62
484 ± 0
496 ± 102
536 ± 0
438 ± 0
502 ± 0
479 ± 0
355 ± 0
Total
36
12 ± 5
557 ± 77
Table 2.2 – Number of even and uneven
footed horses and AAEP lameness scores
Lameness score
0/5 walk, 0/5 trot
1/5 walk, 0/5 trot
1/5 walk, 1/5 trot
Even (N)
Uneven (N)
11
2
0
15
6
2
13
23
4
2.2 Measurement systems and data collection
All horses were weighted before the experiments. Horses were scored for lameness by an
experienced clinician (AAEP lameness scale, score 0-5) at walk and trot on a hard surface and in a
straight line. Furthermore, the forefeet were classified as even or as uneven by the same clinician
(table 2.2). Prior to data collection, all horses were habituated to the data collection area.
The feet were cleaned with isopropyl alcohol. Digital images were taken of the hoof and lower limb
of each foot prior to and following motion capture. One image was taken of the solar surface of the
hoof, with the optical axis of the camera aligned perpendicular to the solar surface of the hoof. The
second image was taken of the heels whilst the limb was unloaded, with the optical axis of the
camera aligned perpendicular to the palmar aspect of the heels. In both images an incremented scale
was held in the field of view to calibrate the images.
After the first set of images was taken, static and tracking retro-reflective markers were attached to
the skin of the distal forelimbs, as depicted in figure 2.1. Static markers were used to define the
length and orientation of the distal limb segments and were removed after a static trial. Tracking
markers were referenced to the static markers in the static trial, which could then be used to track
the movement of the segment during locomotion.
Figure 2.1 – Locations of
static
and
tracking
markers on the distal
part of the right forelimb
(left: dorsal aspect; right:
lateral aspect).
In order to determine the proximal location of the third metacarpal bone, static markers were
attached to the skin overlying the dorsal edge of the head of the medial and lateral splint bones.
Distally, static markers were placed on the skin overlying the medial and lateral condyles of the third
metacarpal bone, at the proximal attachment site of the medial and lateral collateral ligaments of
the fetlock joint (Clayton et al., 2007a). Static markers were also mounted over the medial and lateral
tuberosities of the proximal aspect of the proximal phalanx. At the distal aspect of the proximal
phalanx, static markers were placed over the medial and lateral tubercle, at the attachment site of
the medial and lateral collateral ligament of the proximal interphalangeal joint (Clayton et al., 2007a;
Clayton et al., 2007b). At the dorsal hoof wall, two static markers were attached; one at the coronary
band and the other at the distal border of the hoof.
5
A cluster of four tracking markers was mounted to the skin overlying the dorsolateral mid-shaft of
the third metacarpal bone. A cluster comprising three tracking markers was placed over the
dorsolateral aspect of the proximal phalanx.
During a static trial, the positions of both static and tracking markers were measured, while the horse
was standing square, using an eight-camera Qualisys Oqus 3+ motion capture system. After the static
trial, static markers of third metacarpal bone and proximal phalanx were removed, as their position
relative to the tracking markers was defined using the calibrated anatomical systems technique
(CAST) (Cappozzo et al., 1995; Hobbs et al., 2006).
A handler led the horse over a Kistler Z4852C force plate (60 x 90 cm), at trot in a straight line and at
a constant velocity. The force plate and the surrounding running track were covered with a rubber
mat, and the force plate was surrounded by the motion capture system (figure 2.2).
The kinematic data were collected at a frequency of 250 Hz and the tracking markers were filtered
using a 4th order Butterworth filter with a cut-off frequency of 12 Hz. The ground reaction forces
(GRFs) from the force plate were collected at a frequency of 1000 Hz and subsequently downsampled to 250 Hz. A minimum of 3 measurements was recorded and analyzed for each forelimb.
Figure 2.2 – Experimental setup, with eight motion capture camera’s surrounding the force plate. The
force plate was positioned under the rubber mat (between the two grey lines).
6
2.3 Data processing and analysis
2.3.1
Definition of uneven feet based on objective quantifiable variables
Hoof measurements from digital images
From the digital images, three measurements were performed in duplicate for each forelimb using
Adobe Photoshop:
 Hoof area: on the image of the solar surface of the hoof, a line was drawn joining the most
palmar aspect of both heel buttresses or heels of the horseshoe. This line was joined to a line
following the contour of the hoof wall or horseshoe. Hoof area was defined as the area enclosed
by these lines (figure 2.3 A and B).
 Hoof width: width of the hoof was defined as the distance between the medial and lateral hoof
wall, measured at the broadest part of the solar surface of the hoof (figure 2.3 A and B).
 Heel height: on the image of the palmar aspect of the heels, a line was drawn from the medial to
the lateral heel. The perpendicular distance from this line to the lowest point of the hairline was
measured, both medially and laterally. Heel height was defined as the mean of these medial and
lateral distances (figure 2.3 C and D).
Figure 2.3 – Hoof measurements from digital images of horses without (A and C)
and with (B and D) horseshoes. (A and B) Hoof area was defined as the area
enclosed by the red line; hoof width was represented by the length of the blue
line. (C and D) Heel height was calculated from the mean length of the medial
and lateral blue lines.
7
Segment definition from motion capture system
Initially two mediolateral axes were computed for the proximal phalanx and third metacarpal bone
from the static marker positions on each segment. The proximal axis was represented from the
proximal medial marker to the proximal lateral marker. The distal axis was represented by a line from
the distal medial marker to the distal lateral marker of the bone. A longitudinal axis was defined as
running at the midpoint of and perpendicular to the proximal axis and bisected the distal
mediolateral axis. This allowed the flexion-extension axis of the fetlock joint to be located.
The flexion-extension axis of the fetlock joint was computed from dynamic data of the horse at trot,
using the method described by Schwartz et al. (2005). The functional joint center of the fetlock was
then located as the intersection of the flexion-extension axis with the longitudinal axis of the third
metacarpal bone. Once the fetlock joint had been located, the proximal end of the proximal phalanx
and the distal end of the third metacarpal bone were adjusted to the location of the fetlock joint.
The following parameters were calculated from the data of the motion capture system:
 Hoof angle: the angle of the line joining the proximal and distal marker at the dorsal hoof wall.
Every individual foot was categorized as upright (hoof angle > 55°), medium (hoof angle between
50° and 55°) or flat (hoof angle < 50°). This categorization was based upon the normal hoof angle
range of 50° to 55° reported by Stashak et al. (2002).
 Length and angle of proximal phalanx: length and angle of the segment as represented by a line
running from the distal mediolateral axis of the proximal phalanx to the functional joint center of
the fetlock.
 Length of third metacarpal bone: length of the segment as represented by a line running from
the proximal mediolateral axis of the third metacarpal bone to the functional joint center of the
fetlock.
 Fetlock angle: angle at the point where the longitudinal axis of the proximal phalanx intersected
the longitudinal axis of the third metacarpal bone.
8
2.3.2
Functional parameters
From the force plate data, the following functional parameters were calculated for each forelimb
using MATLAB 8.0 (figures 2.4, 2.5 and 2.6):
 Total impulse normalized to body mass:
o Total vertical impulse (JFz, or area under the Fz-time curve)
o Total braking impulse (JFxneg, or area under the negative Fx-time curve)
o Total propulsive impulse (JFxpos, or area under the positive Fx-time curve)
 Peak ground reaction force normalized to body mass:
o Peak vertical force (Fzmax)
o Peak braking force (Fxmin)
o Peak propulsive force (Fxmax)
o Peak resultant vertical-longitudinal force (Frmax; the magnitude of the resultant forces
were obtained by the following formula: (Fz2 + Fx2)1/2)
 Vertical force at the time point of Frmax (Fz at Frmax)
 Longitudinal force at the time point of Frmax (Fx at Frmax)
 Angle of resultant vertical-longitudinal force vector (Angle Frmax, defined by the following
calculation: Angle Frmax = tan-1(Fx at Frmax/Fz at Frmax))
 Time during which the hoof was in contact with the ground surface (stance duration)
 Time to reach the transition from a braking to a propulsive force (tFxzero, % of stance duration)
 Time to reach peak ground reaction force:
o Time to reach Fzmax (tFzmax, % of stance duration)
o Time to reach Fxmin (tFxmin, % of stance duration)
o Time to reach Fxmax (tFxmax, % of stance duration)
o Time to reach Frmax (tFrmax, % of stance duration)
Figure 2.4 – Longitudinal force-time graph.
The vertical and horizontal coordinates of the
red square represent Fxmin and tFxmin,
respectively. Fxmax and tFxmax are
represented by the vertical and horizontal
coordinates of the green square, respectively.
tFxzero is located at the point of the black
square. Shaded areas represent JFxneg (dark
shading) and JFxpos (light shading).
Figure 2.5 – Vertical force-time graph. The
vertical and horizontal coordinates of the red
square represent Fzmax and tFzmax,
respectively. The shaded area represents JFz.
9
Figure 2.6 – Resultant force-time graph (A)
and vertical and longitudinal force-time
graphs (B). The vertical and horizontal
coordinates of the green square represent
Frmax and tFrmax, respectively (A). The
vertical coordinates of the red and blue
square represent Fz at Frmax and Fx at
Frmax, respectively.
From a plot of vertical ground reaction force (Fz, measured by the force plate) against vertical
displacement of the functional joint center of the fetlock (Fetz, measured by the motion capture
system), the following parameters were defined using Microsoft Excel (figure 2.7):
 Maximal vertical displacement of the fetlock joint (Fetzmax; downward vertical displacement of
the fetlock joint from the start of the stance phase to its lowest position)
 Vertical force at maximal vertical fetlock displacement (Fz at Fetzmax; normalized to body mass)
 Stiffness: slope of the Fz-Fetz curve from the start of the stance phase to the point of maximal
vertical displacement of the fetlock joint
Figure 2.7 – Vertical ground reaction force
(GRF) and vertical displacement of the
fetlock joint during the stance phase. Fetzmax
and Fz at Fetzmax were calculated from the
horizontal and vertical coordinates of the
red square. Stiffness was calculated from the
slope of the red line joining the black and the
red square.
10
2.4 Statistical analysis
6 out of 19 functional parameters were transformed to meet the assumption of normality, using the
ladder of powers transformation (Velleman and Hoaglin, 1981). All analyses were performed in SPSS
21.0 software and results were considered significant if P < 0.05.
2.4.1
Definition of uneven feet based on objective quantifiable variables
For the anatomical hoof and limb measurements of each horse, absolute differences between the
forefeet were calculated. Subsequently, mean values were calculated separately for horses with even
feet and for horses with uneven feet, following visual classification.
A discriminant analysis based upon absolute anatomical differences of all 36 horses was performed
to objectively determine whether a horse has uneven feet or not. To evaluate whether the variables
(i.e. absolute anatomical differences) were significantly different between even and uneven footed
horses, an independent samples t-test was conducted. Variables were included in the discriminant
analysis only if they were significantly different between horses with even and uneven feet.
Moreover, Pearson correlation coefficients between the variables were calculated.
To further examine the reliability of the absolute hoof measurements from the digital images (which
were performed in duplicate) the spreadsheet of Hopkins (2000) was used to determine the
measurement errors.
2.4.2
Relationship between unevenness and functional parameters
To test if uneven footed horses showed more functional asymmetries between the forefeet than
even footed horses, the following procedure was performed: For each horse, the foot with the
highest hoof angle was classified as ‘highest hoof angle’ (HHA) foot, and the foot with the lowest
hoof angle was classified as ‘lowest hoof angle’ (LHA) foot. Based upon the visual classification as
well as upon the discriminant function, full factorial MANOVA followed by ANOVA tests were
conducted on functional parameters, separately for horses with even feet and for horses with
uneven feet. ‘Foot category (LHA/HHA)’ was used as fixed factor and ‘horse’ was used as random
factor.
Since lameness could affect the ground reaction forces (Back et al., 2007; Clayton et al., 2000; Morris
and Seeherman, 1987; Weishaupt et al., 2006), horses that showed a visually detectable lameness at
trot (n = 2, table 2.2) were excluded from the analyses. Horses that were lame at walk but not at trot
(n = 8, table 2.2) were not excluded, since measurements were performed at trot and because of the
clinically proposed relationship with unevenness, as described earlier in chapter 1.
11
2.4.3
Relationship between individual foot conformation and functional parameters
In order to test whether the functional parameters were different between foot categories (upright,
medium, flat), full factorial MANOVA, followed by ANOVA were used. ‘Foot category
(upright/medium/flat)’ was set as fixed factor and ‘horse’ was set as random factor. Scheffé’s post
hoc test was used to compare foot categories for any variables that were found significant for the
main effect ‘foot category’. Horses that were lame at trot were excluded from the analyses.
2.4.4
Relative weight of conformational differences between the forefeet and of individual foot
conformation
To evaluate the relative weight of the conformational differences between the feet and of individual
foot conformation on the significant results of the analyses described in section 2.4.2 and 2.4.3,
multiple linear regression analyses were performed. For the functional parameters of each horse,
mean values were calculated per foot. The functional parameters were tested individually by
multiple regression analysis. ‘Difference in hoof angle’ and ‘absolute hoof angle’ were set as
independent variables to test their relative influence on the functional parameter. Again, horses that
were lame at trot were excluded from the analyses.
12
3. Results
3.1 Definition of uneven feet based on objective quantifiable
variables
Table 3.1 shows mean values of the absolute differences in anatomical measurements between the
forefeet. Mean values were calculated separately for horses with even and uneven feet, based upon
the visual classification. Only heel height and hoof angle showed a significantly larger mean ± s.e.
difference between the forefeet of horses with uneven feet (heel height: 1.10 ± 0.20 cm, hoof angle:
6 ± 1°) compared to horses with even feet (heel height: 0.51 ± 0.06 cm, hoof angle: 3 ± 0°). For
absolute differences in hoof area, hoof width, proximal phalangeal bone (Pprox) angle, fetlock angle,
third metacarpal bone (MC3) length and Pprox length, no significant differences were found between
even and uneven footed horses.
Table 3.1 – Comparison of mean absolute anatomical differences between the forefeet
of even and uneven footed horses.
Difference heel height (cm)
Difference hoof angle (°)
Difference hoof area (cm²)
Difference hoof width (cm)
Difference Pprox angle (°)
Difference fetlock angle (°)
Difference MC3 length (cm)
Difference Pprox length (cm)
Even (n = 13)
Mean ± s.e.
Uneven (n = 23)
Mean ± s.e.
Independent samples t-test
P-value
0.51 ± 0.06
3±0
17.28 ± 4.92
1.38 ± 0.33
10 ± 2
9±2
0.84 ± 0.20
0.66 ± 0.12
1.10 ± 0.20
6±1
11.14 ± 2.22
1.14 ± 0.21
8±1
9±1
0.49 ± 0.06
0.61 ± 0.09
0.009
0.004
0.271
0.556
0.473
0.895
0.114
0.731
If a parameter was significantly different between horses with even feet and horses with uneven
feet, cells are colored green. For the other parameters, cells are colored red.
The measurement error of the hoof area was 6.9 cm2. Hoof width and heel height were measured
with errors of 3.7 mm and 1.6 mm, respectively.
There was a strong positive correlation between absolute difference in heel height and absolute
difference in hoof angle (Pearson’s r = 0.630, P = 0.000). So a large absolute difference in heel height
between the forefeet was associated with a large absolute difference in hoof angle, and vice versa.
When the foot with the steepest hoof angle was compared to the foot with the lowest hoof angle for
each horse, a positive correlation was found between the real difference in heel height and the real
difference in hoof angle (Pearson’s r = 0.679, P = 0.000). When the foot with the largest heel height
was compared to the foot with the lowest heel height for each horse, a positive correlation between
the real difference in heel height and the real difference in hoof angle was found (Pearson’s r =
0.631, P = 0.000). This means that for both methods a large real difference in heel height between
the forefeet was associated with a large real difference in hoof angle in the same direction. When
13
considering the original measurements instead of the differences between hooves, Pearson’s r
between heel height and hoof angle was 0.340 (P = 0.004).
The discriminant function with the highest predictive power was based solely on the difference in
hoof angle between the forefeet. Heel height added no more predictive power to the function, and
heel height in itself did not yield a better model. The function revealed a significant association
between the classification ‘even/uneven’ and the difference in hoof angle between the forefeet, with
a canonical correlation of 0.385 (P = 0.020). Box’s M test indicated that the assumption of equality of
covariance matrices was violated (P = 0.000). However, discriminant analysis is relatively robust to
violations of this assumption (Lachenbruch, 1975).
The discriminant analysis was based on the following formula:
D = -1.151 + 0.243 * [Absolute difference in hoof angle]
The cut-off value was -0.793, which means that all horses with an absolute difference in hoof angle
higher than 1.5° were classified as uneven.
Table 3.2 – Classification resultsa,c of the discriminant analysis
Predicted Group
Membership
Even
Original
Count
%
Crossvalidatedb
Count
%
Uneven
Total
Even
3
10
13
Uneven
4
19
23
Even
23.1
76.9
100.0
Uneven
17.4
82.6
100.0
Even
2
11
13
Uneven
7
16
23
Even
15.4
84.6
100.0
Uneven
30.4
69.6
100.0
a. 61,1% of original grouped cases correctly classified.
b. Cross validation is done only for those cases in the analysis. In
cross validation, each case is classified by the functions derived from
all cases other than that case.
c. 50,0% of cross-validated grouped cases correctly classified.
In table 3.2 the classification results of the discriminant analysis are depicted. Based upon the
original classification by the discriminant function, 7 horses were classified as even and 29 horses
were classified as uneven. The discriminant function showed a sensitivity of 82.6%. This means that
of the 23 horses which were visually classified as uneven, 19 were classified as uneven by the
discriminant function as well. The discriminant function showed a specificity of 23.1%. This means
that of the 13 horses which were visually classified as even, 3 were also classified as even by the
discriminant function. Overall (i.e. even and uneven), 61.1% of the horses were correctly classified.
After cross validation, 9 horses were classified as even and 27 horses were classified as uneven. In
this case, the discriminant function shows a sensitivity of 69.6%. This means that of 23 horses which
were visually classified as uneven, 16 were classified as uneven by the discriminant function as well.
14
The discriminant function showed a specificity of 15.4%. This means that of the 11 horses that were
visually classified as even, 2 were also classified as even by the discriminant function. Overall (i.e.
even and uneven), 50.0% of the horses were correctly classified.
3.2 Foot classification
Table 3.3 shows the distribution of the feet over the different categories. In this categorization and in
the further analyses, the two horses that were lame at trot were not included.
Table 3.3 – Number of feet and mean ± s.e. hoof angle per foot category.
Visual classification – uneven
Visual classification – even
LHA foot
HHA foot
Flat
Medium
Upright
6
5
2
48 ± 0°
51
2
49 ± 0°
62
7
52
8
48 ± 0°
± 1°
± 5° 51
4
± 1°
59
12
52
13
± 0°
13
± 3° 54
6
60
± 1°
± 1°
LHA foot
HHA foot
± 2° 53
HHA foot
Flat
Medium
Upright
3
2
2
49 ± 0°
51
2
49 ± 0°
56
3
52
5
49 ± 0°
± 0°
57
± 0°
57
5
51
Upright
13
7
1
47
± 1° 52
4
6
48
± 0°
56
7
± 0°
47
53
± 1°
8
± 1°
58
14
52
± 0° 49
± 0°
± 1° 54
9
58
± 1°
21
± 1°
42
± 1° 51
± 1°
± 1°
LHA foot
HHA foot
Flat
Medium
Upright
16
10
1
47
± 1°
± 1°
51
6
48
14
± 1° 52
51
21
± 1°
Discriminant function – uneven
7
± 1° 52
± 1°
19
± 1°
7
2
± 1°
Medium
26
Discriminant function – even
LHA foot
Flat
66
11
± 0°
53
22
47
± 0°
± 1°
± 0°
± 0°
± 0° 49
10
59
21
52
27
± 1° 54
11
59
± 1° 52
± 1°
27
± 1°
54
± 1°
15
3.3 Relationship between unevenness and functional parameters
3.3.1
Longitudinal ground reaction force
Braking ground reaction force
Table 3.4 shows the results of the ANOVA’s for braking GRF parameters. Based upon the visual
classification (VC) as well as upon the discriminant function (DF), the peak braking GRF was
significantly different between the forefeet of horses with uneven feet, but not between the forefeet
of horses with even feet. In horses with uneven feet, the LHA showed a larger mean peak braking
force (VC: 0.501 N/kg, DF: 0.546 N/kg) compared to the HHA foot (VC: 0.394 N/kg, DF: 0.444 N/kg).
Only in the case of classification based upon the discriminant function, horses with uneven feet
showed a significant difference in total braking impulse between the forefeet, in contrast to horses
with even feet. This difference occurred in combination with a difference in the moment of zero
longitudinal force. In horses with uneven feet, the LHA foot showed a larger mean braking impulse in
combination with a later moment of zero longitudinal force (0.051 N*s/kg and 47.3%, respectively)
compared to the HHA foot (0.041 N*s/kg and 45.2%, respectively).
For horses with even feet as well as for horses with uneven feet, no significant differences in stance
duration and the time point of peak braking GRF were found between the forefeet.
Table 3.4 – Comparison of the braking ground reaction force parameters of the LHA foot with those of
the HHA foot in horses with uneven feet as well as in horses with even feet.
Visual classification
Uneven
Even
JFxneg
Fxmin
tFxmin
tFxzero
P-value
0.084
Discriminant function
Uneven
Even
0.848
0.025
0.477
Mean LHA [95% CI] (N*s/kg)
0.046
[0.043
0.049]
0.058
[0.054
0.063]
0.051
[0.048
0.053]
0.049
[0.044
0.055]
Mean HHA [95% CI] (N*s/kg)
0.038
[0.035
0.040]
0.057
[0.053
0.061]
0.041
[0.039
0.043]
0.057
[0.051
0.064]
Mean LHA [95% CI] (N/kg)
0.501
[0.475
0.528]
0.626
[0.579
0.674]
0.546
[0.521
0.571]
0.552
[0.487
0.620]
Mean HHA [95% CI] (N/kg)
0.394
[0.371
0.418]
0.621
[0.579
0.664]
0.444
[0.423
0.466]
0.600
[0.533
0.672]
P-value
0.029
P-value
0.924
0.971
0.017
0.441
0.551
0.755
0.768
Mean LHA [95% CI] (%)
27.3
[26.7
27.9]
27.4
[26.8
28.0]
27.2
[26.7
27.7]
28.0
[27.0
29.0]
Mean HHA [95% CI] (%)
27.3
[26.7
27.9]
27.0
[26.5
27.6]
27.1
[26.6
27.5]
27.8
[26.7
28.8]
P-value
0.204
0.746
0.034
0.178
Mean LHA [95% CI] (%)
47.4
[46.7
48.1]
46.1
[45.3
47.0]
47.3
[46.7
47.9]
45.5
[44.2
46.8]
Mean HHA [95% CI] (%)
45.9
[45.1
46.6]
45.8
[45.0
46.6]
45.2
[44.6
45.8]
48.2
[46.9
49.5]
Stance duration P-value
0.771
0.985
0.905
0.584
Mean LHA [95% CI] (s)
0.320
[0.317
0.324]
0.320
[0.315
0.325]
0.319
[0.316
0.323]
0.324
[0.317
0.330]
Mean HHA [95% CI] (s)
0.320
[0.316
0.323]
0.320
[0.315
0.324]
0.320
[0.316
0.323]
0.320
[0.313
0.327]
The table shows ANOVA results for both the visual classification and the discriminant function classification. For
each analysis, P-values, means and 95% confidence interval (CI) are presented. Green cells contain significant
results.
16
Propulsive ground reaction force
Table 3.5 shows the results of the ANOVA’s for propulsive GRF parameters. For both classification
methods, none of the propulsive force parameters were significantly different between the forefeet
of horses with even and uneven feet.
Table 3.5 – Comparison of the propulsive ground reaction force parameters of the LHA foot with those
of the HHA foot in horses with uneven feet as well as in horses with even feet.
Visual classification
Uneven
Even
JFxpos
Fxmax
tFxmax
P-value
0.288
Discriminant function
Uneven
Even
0.896
0.068
0.251
Mean LHA [95% CI] (N*s/kg)
0.083
[0.081
0.086]
0.097
[0.092
0.101]
0.085
[0.082
0.087]
0.103
[0.097
0.110]
Mean HHA [95% CI] (N*s/kg)
0.088
[0.085
0.090]
0.097
[0.093
0.101]
0.091
[0.088
0.093]
0.094
[0.088
0.100]
P-value
0.662
0.726
0.197
0.344
Mean LHA [95% CI] (N/kg)
0.766
[0.748
0.784]
0.897
[0.865
0.930]
0.789
[0.772
0.807]
0.914
[0.871
0.959]
Mean HHA [95% CI] (N/kg)
0.777
[0.759
0.796]
0.909
[0.880
0.939]
0.817
[0.800
0.835]
0.856
[0.816
0.899]
P-value
0.891
0.688
0.382
0.238
Mean LHA [95% CI] (%)
73.6
[73.3
74.0]
70.9
[70.5
71.3]
72.7
[72.4
73.0]
72.1
[71.5
72.8]
Mean HHA [95% CI] (%)
73.6
[73.2
74.0]
70.7
[70.3
71.1]
72.3
[72.0
72.6]
73.1
[72.4
73.8]
The table shows ANOVA results for both the visual classification and the discriminant function classification. For
each analysis, P-values, means and 95% confidence interval (CI) are presented.
17
3.3.2
Vertical ground reaction force
Table 3.6 shows the results of the ANOVA’s for vertical GRF parameters. For both classification
methods, the peak vertical GRF was significantly different between the forefeet of horses with
uneven feet, but not between the forefeet of horses with even feet. In horses with uneven feet, the
mean vertical GRF was higher in the LHA foot (VC: 10.585 N/kg, DF: 10.874 N/kg) compared to the
HHA foot (VC: 10.296 N/kg, DF: 10.624 N/kg).
Only in the case of visual classification, horses with uneven feet showed a significant difference in
total vertical impulse between the forefeet, in contrast to horses with even feet. In horses with
uneven feet, the LHA foot showed a larger mean vertical impulse (2.062 N*s/kg) compared to the
HHA foot (2.012 N*s/kg).
For horses with even feet as well as for horses with uneven feet, no significant differences in stance
duration and the time point of peak vertical GRF were found between the forefeet.
Table 3.6 – Comparison of the vertical ground reaction force parameters of the LHA foot with those of
the HHA foot in horses with uneven feet as well as in horses with even feet.
Visual classification
Uneven
Even
JFz
Fzmax
tFzmax
P-value
0.029
Discriminant function
Uneven
Even
0.520
0.247
0.071
Mean LHA [95% CI] (N*s/kg)
2.062
[2.046
2.078]
2.104
[2.083
2.125]
2.076
[2.061
2.091]
2.087
[2.063
2.111]
Mean HHA [95% CI] (N*s/kg)
2.012
[1.996
2.028]
2.084
[2.065
2.103]
2.036
[2.022
2.050]
2.053
[2.029
2.077]
P-value
0.025
0.422
0.026
0.499
Mean LHA [95% CI] (N/kg)
10.585
[10.504
10.666]
11.322
[11.188
11.456]
10.874
[10.791
10.958]
10.838
[10.700
10.975]
Mean HHA [95% CI] (N/kg)
10.296
[10.213
10.379]
11.221
[11.101
11.342]
10.624
[10.543
10.705]
10.748
[10.611
10.886]
P-value
0.630
0.669
0.865
0.308
Mean LHA [95% CI] (%)
46.3
[45.9
46.8]
43.7
[43.1
0.444]
45.4
[45.0
45.9]
44.8
[44.0
45.6]
Mean HHA [95% CI] (%)
46.6
[46.1
47.1]
43.6
[43.0
0.441]
45.4
45.0
45.8]
45.3
[44.5
46.2]
Stance duration P-value
0.771
0.985
0.905
0.584
Mean LHA [95% CI] (s)
0.320
[0.317
0.324]
0.320
[0.315
0.325]
0.319
[0.316
0.323]
0.324
[0.317
0.330]
Mean HHA [95% CI] (s)
0.320
[0.316
0.323]
0.320
[0.315
0.324]
0.320
[0.316
0.323]
0.320
[0.313
0.327]
The table shows ANOVA results for both the visual classification and the discriminant function classification. For
each analysis, P-values, means and 95% confidence interval (CI) are presented. Green cells contain significant
results.
18
3.3.3
Resultant vertical-longitudinal ground reaction force
Table 3.7 shows the results of the ANOVA’s for resultant GRF parameters. Like the peak vertical
impulse, the peak resultant vertical-longitudinal GRF was significantly different between the forefeet
of horses with uneven feet, but not between the forefeet of horses with even feet. Both classification
methods showed that horses with uneven feet had a higher mean peak resultant GRF in the LHA foot
(VC: 10.588 N/kg, DF: 10.879 N/kg) than in the HHA foot (VC: 10.300 N/kg, DF: 10.630 N/kg).
In horses with uneven feet, the LHA foot also had a higher mean vertical GRF at the point of Frmax
(VC: 10.585 N/kg, DF: 10.875 N/kg) compared to the HHA foot (VC: 10.296 N/kg, DF: 10.626 N/kg).
For horses with even feet as well as for horses with uneven feet, no significant differences in the
mean angle and time point of the peak resultant GRF were found between the forefeet. The mean
longitudinal GRF at the time point of Frmax showed no significant differences as well.
Table 3.7 – Comparison of the resultant ground reaction force parameters of the LHA foot with those
of the HHA foot in horses with uneven feet as well as in horses with even feet.
Visual classification
Uneven
Even
Frmax
P-value
0.026
Fz at Frmax
Fx at Frmax
0.429
0.026
0.517
Mean LHA [95% CI] (N/kg)
10.588
[10.507
10.669]
11.330
[11.196
11.463]
10.879
[10.796
10.963]
10.842
[10.705
10.979]
Mean HHA [95% CI] (N/kg)
10.300
[10.217
10.382]
11.231
[11.110
11.351]
10.630
[10.549
10.710]
10.756
[10.619
10.893]
Angle Frmax P-value
tFrmax
Discriminant function
Uneven
Even
0.196
0.966
0.113
0.459
Mean LHA [95% CI] (°)
-0.224
[-0.427
-0.021]
-0.675
[-1.016
-0.334]
-0.411
[-0.608
-0.214]
-0.341
[-0.791
0.109]
Mean HHA [95% CI] (°)
0.226
[0.020
0.433]
-0.690
[-0.997
-0.383]
0.042
[-0.148
0.233]
-0.766
[-1.216
-0.316]
P-value
0.723
0.597
0.998
0.935
Mean LHA [95% CI] (%)
46.3
[45.8
46.8]
43.7
[43.1
44.3]
45.4
[45.0
45.8]
44.8
[44.0
45.6]
Mean HHA [95% CI] (%)
46.5
[46.0
47.0]
43.5
[42.9
44.0]
45.4
[45.0
45.8]
44.8
[44.0
45.7]
Mean LHA [95% CI] (N/kg)
10.585
[10.504
10.666]
11.325
[11.191
11.458]
10.875
[10.792
10.959]
10.839
[10.702
10.976]
Mean HHA [95% CI] (N/kg)
10.296
[10.213
10.379]
11.226
[11.106
11.347]
10.626
[10.545
10.706]
10.752
[10.615
10.889]
P-value
0.026
P-value
0.434
0.197
0.026
0.889
0.514
0.139
0.462
Mean LHA [95% CI] (N/kg)
-0.050
[-0.086
-0.014]
-0.129
[-0.195
-0.062]
-0.084
[-0.120
-0.047]
-0.066
[-0.156
0.023]
Mean HHA [95% CI] (N/kg)
0.032
[-0.005
0.069]
-0.138
[-0.198
-0.078]
-0.005
[-0.040
0.031]
-0.144
[-0.233
-0.055]
The table shows ANOVA results. For each analysis, P-values, means and 95% confidence interval (CI) are
presented. Green cells contain significant results.
19
3.3.4
Force-displacement curve
Table 3.8 shows the results of the ANOVA’s for maximal vertical fetlock displacement, force at
maximal fetlock displacement and stiffness.
For both classification methods, maximal vertical fetlock displacement was significantly different
between the forefeet of horses with uneven feet, but not between the forefeet of horses with even
feet. In horses with uneven feet, the mean maximal vertical fetlock displacement of the LHA foot was
larger (VC: 0.051 m, DF: 0.049 m) than that of the HHA foot (VC: 0.046 m, DF: 0.045 m). For horses
with even feet as well as for horses with uneven feet, no significant differences in mean vertical force
at the moment of maximal vertical fetlock displacement were found between the forefeet.
Both classification methods showed a significant difference in stiffness between uneven feet, but not
between even feet. For horses with uneven feet, stiffness was lower in the LHA foot (VC: 110.1 kN/m,
DF: 120.1 kN/m) than in the HHA foot (VC: 118.9 kN/m, DF: 127.8 kN/m). A schematic representation
of the stiffness is depicted in figure 3.1.
Table 3.8 – Comparison of the force-displacement curve parameters of the LHA foot with those of the
HHA foot in horses with uneven feet as well as in horses with even feet.
Visual classification
Uneven
Even
P-value
Fetzmax
Fz at Fetzmax
Stiffness
0.007
Discriminant function
Uneven
Even
0.228
0.006
0.325
Mean LHA [95% CI] (m)
0.051
[0.050
0.052]
0.045
[0.044
0.047]
0.049
[0.048
0.050]
0.046
[0.044
0.048]
Mean HHA [95% CI] (m)
0.046
[0.045
0.047]
0.044
[0.042
0.045]
0.045
[0.044
0.046]
0.044
[0.042
0.047]
P-value
0.146
0.623
0.161
0.493
Mean LHA [95% CI] (N/kg)
9.987
[9.876
10.098]
10.781
[10.632
10.929]
10.323
[10.218
10.427]
10.214
[10.051
10.378]
Mean HHA [95% CI] (N/kg)
9.624
[9.624
9.849]
10.710
[10.575
10.846]
10.119
[10.018
10.220]
10.124
[9.958
10.290]
P-value
0.022
0.175
0.008
0.531
Mean LHA [95% CI] (kN/m)
110.1
[106.8
113.5]
137.1
[132.6
141.6]
120.1
[117.1
123.0]
123.3
[116.6
130.0]
Mean HHA [95% CI] (kN/m)
118.9
[115.5
122.3]
140.9
[136.7
145.0]
127.8
[124.9
130.6]
126.8
[120.0
133.5]
The table shows ANOVA results. For each analysis, P-values, means and 95% confidence interval (CI) are
presented. Green cells contain significant results.
6000
A
5000
4000
3000
LHA foot
2000
HHA foot
1000
0
Vertical GRF (N)
Vertical GRF (N)
6000
B
5000
4000
3000
LHA foot
2000
HHA foot
1000
0
0
0.02
0.04
0.06
Vertical displacement of fetlock joint (m)
0
0.02
0.04
0.06
Vertical displacement of fetlock joint (m)
Figure 3.1 – Schematic representation of stiffness based upon visual classification (A), and
discriminant function classification (B). The blue curve represents the lower hoof angle (LHA) foot and
the red curve represents the higher hoof angle (HHA) foot. From left to right, the squares represent
the start of the stance phase and the point of maximal vertical displacement of the fetlock joint.
Stiffness is represented by the slope of the line joining the two squares.
20
3.4 Relationship between individual foot conformation and
functional parameters
None of the functional parameters were significantly different between feet categorized as flat,
medium or upright, as depicted in table 3.9.
Table 3.9 – Functional differences between feet categorized as flat, medium or upright.
P-value
Flat
Medium
Upright
JFxneg
0.057
Mean [95% CI] (N*s/kg)
0.049 [0.046
0.053]
0.048 [0.045
0.051]
0.039 [0.036
0.042]
Fxmin
0.057
Mean [95% CI] (N/kg)
0.521 [0.491
0.553]
0.531 [0.502
0.562]
0.430 [0.395
0.466]
tFxmin
0.504
Mean [95% CI (%)]
27.4 [26.9
27.9]
27.0 [26.5
27.5]
27.4 [26.8
28.1]
JFxpos
0.249
Mean [95% CI] (N*s/kg)
0.083 [0.080
0.086]
0.092 [0.089
0.095]
0.096 [0.092
0.100]
Fxmax
0.516
Mean [95% CI] (N/kg)
0.751 [0.732
0.770]
0.874 [0.852
0.896]
0.862 [0.835
0.891]
tFxmax
0.686
Mean [95% CI] (%)
73.1 [72.7
73.4]
72.4 [72.0
72.7]
72.9 [72.4
73.3]
tFxzero
0.182
Mean [95% CI] (%)
47.4 [46.7
48.1]
46.0 [45.3
46.7]
45.0 [44.1
45.9]
Stance
duration
0.586
Mean [95% CI] (s)
0.326 [0.322
0.330]
0.312 [0.309
0.316]
0.315 [0.310
0.319]
JFz
0.316
Mean [95% CI] (N*s/kg)
2.069 [2.053
2.086]
2.030 [2.014
2.046]
2.039 [2.018
2.059]
Fzmax
0.256
Mean [95% CI] (N/kg)
tFzmax
0.546
Mean [95% CI] (%)
Frmax
0.256
Mean [95% CI] (N/kg)
10.559 [10.470 10.648]
10.842 [10.755 10.929]
Angle Frmax
0.207
Mean [95% CI] (°)
-0.399 [-0.636
-0.267 [-0.498
tFrmax
0.417
Mean [95% CI] (%)
45.5 [45.1
Fz at Frmax
0.257
Mean [95% CI] (N/kg)
10.555 [10.466 10.644]
10.837 [10.750 10.924]
Fx at Frmax
0.230
Mean [95% CI] (N/kg)
-0.081 [-0.126
-0.037]
-0.058 [-0.101
-0.014]
0.017 [-0.039
0.074]
Fetzmax
0.233
Mean [95% CI] (m)
0.049 [0.047
0.050]
0.045 [0.043
0.046]
0.048 [0.046
0.049]
Fz at Fetzmax
0.346
Mean [95% CI] (N/kg)
9.989 [9.873
10.106]
Stiffness
0.383
Mean [95% CI] (kN/m)
119.6 [116.2
123.1]
10.554 [10.465 10.644]
45.7 [45.2
46.1]
-0.163]
46.0]
10.835 [10.748 10.922]
45.4 [45.0
45.3 [44.8
45.9]
-0.037]
45.8]
10.223 [10.114 10.331]
125.9 [122.7
129.1]
10.804 [10.690 10.918]
45.7 [45.1
46.3]
10.808 [10.694 10.922]
0.186 [-0.116
0.487]
45.6 [45.1
46.3]
10.805 [10.691 10.919]
10.530 [10.382 10.679]
127.8 [123.4
132.2]
The table shows ANOVA results. For each analysis, P-values, means and 95% confidence interval (CI) are
presented.
21
3.5 Relative weight of conformational differences between the
forefeet and of individual foot conformation
As depicted in table 3.10, only the multiple regression analysis of tFxzero showed a significant
moderate association with ‘absolute hoof angle’ and ‘difference in hoof angle’ (multiple R = 0.411, P
= 0.002). For this parameter, the standardized regression coefficient (Beta) of the difference in hoof
angle was 1.6 times larger in magnitude (-0.289) than that of the absolute hoof angle (-0.180).
Furthermore, the ‘difference in hoof angle’ was significant (P = 0.032) while ‘absolute hoof angle’ had
a P-value of 0.177. For the peak vertical GRF, peak resultant GRF and the vertical force at the time
point of Frmax, the multiple regression models were close to significance, with P-values of 0.051,
0.052 and 0.052, respectively. The standardized regression coefficients (Beta) of the difference in
hoof angle and the absolute hoof angle were comparable in magnitude (with absolute values of
around 0.3), but opposite in direction. For the maximal vertical fetlock displacement, the
standardized regression coefficient (Beta) of the difference in hoof angle was significant (Beta = 0.284, P = 0.044). However, the entire model was not significant. There were no significant linear
relationships for the other parameters examined.
Table 3.10 – Linear relationship of hoof angle and difference in hoof angle with functional
parameters.
Multiple R
Entire model
R2
Independents
P-value
tFxzero
0.411
0.169
0.002
Fzmax
0.296
0.087
0.051
Frmax
0.295
0.087
0.052
Fz at Frmax
0.295
0.087
0.052
Fetzmax
0.272
0.074
0.088
Absolute hoof angle
Difference hoof angle
Absolute hoof angle
Difference hoof angle
Absolute hoof angle
Difference hoof angle
Absolute hoof angle
Difference hoof angle
Absolute hoof angle
Difference hoof angle
Beta
P-value
-0.180
-0.289
0.292
-0.306
0.291
-0.305
0.292
-0.305
0.027
-0.284
0.177
0.032
0.038
0.030
0.038
0.031
0.038
0.030
0.848
0.044
The table shows the significant results of the multiple linear regression analyses. If the entire model and/or
independents were significant, cells are colored green.
22
4. Discussion
The first aim of this study was the establishment of the definition of uneven feet in horses using
objective quantifiable variables. It appeared that unevenness was best defined by the absolute
differences in dorsal hoof angle between the forefeet, with a cut-off value of 1.5°. Based upon this
definition of uneven feet as well as upon a visual classification method, functional (a)symmetries of
even and uneven footed horses were compared. In horses with uneven feet, the flatter foot showed
a significantly larger maximal horizontal braking and vertical ground reaction force, a larger vertical
fetlock displacement and a less stiff limb spring. A steeper hoof angle was linearly correlated with an
earlier braking-propulsion transition. No significant differences were found between individual feet
categorized as flat, medium or upright. This implies that the conformational differences between the
forefeet were more important for loading characteristics than the conformation of the individual
foot.
4.1 Definition of uneven feet based on objective quantifiable
variables
Our results imply that the classification of feet as uneven is mainly based on differences in hoof
shape, rather than on skeletal asymmetries of the distal limb. The discriminant function with the
highest predictive power is solely based on the absolute difference in hoof angle between the
forefeet. This is in accordance with earlier studies on uneven feet (Moleman et al., 2006; van Heel et
al., 2006a; van Heel et al., 2010).
The cut-off value for unevenness in the current study was represented by a difference in hoof angle
of 1.5°. Higher cut-off values (2.9° and 2.8°) have been reported in previous studies by Moleman et
al. (2006) and van Heel et al. (2010) respectively. However, these studies were performed on
younger Warmblood horses and were based on a different measurement method. Furthermore,
these studies used the mean intra-individual difference in hoof angle as cut-off value instead of a
model based on clinical judgment. Our results suggest that the previously reported cut-off values are
an overestimation of the threshold for visually classifying a horse as uneven. Alternatively, the cut-off
value found in the current study could be prone to subjectivity, as the visual classification was
performed by one clinician.
Unlike the analyses of the functional parameters at trot, the discriminant analysis was performed
with inclusion of the two horses that were lame at trot. This was justified by the fact that the two
lame horses were prime examples of uneven footed horses and both showed the largest difference
in hoof angle between the forefeet of all horses. Moreover, exclusion of these prime examples
leaded to a decrease of the percentage of correctly classified cases.
23
Although the sensitivity of our classification method is satisfactory, the specificity was relatively low.
This might have been partly caused by the fact that no standardized shoeing or trimming protocol
was used. As all horses were brought in by their private owners, they were trimmed by their own
farrier and, for logistic reasons, the time between trimming and the experiments was not
standardized. This, in turn, could have obscured the coherence between difference in hoof angle on
the one hand, and the difference in bone angles on the other. For example, the moment on the distal
interphalangeal joint is known to decrease more in the LHA foot than in the HHA foot during an 8week shoeing interval, whereas the decrease in hoof angle over time is not significantly different for
the LHA foot (3.5°) and the HHA foot (3.6°) (Moleman et al., 2006).
Moreover, the categorization ‘even/uneven’ could be too simple. Perhaps there are more categories
or stages of uneven feet, with each showing different anatomical characteristics. For example, horses
with one normal foot and one upright foot could show other characteristics than horses with one
normal foot and one flat foot, while both have uneven feet. To gain more insight into possible
subcategories, it is necessary to objectively quantify the visual classification of each individual foot.
Therefore, a follow-up study on a large horse population should be performed, scored for
conformation of the individual feet by multiple observers. Horses must be monitored during a
shoeing interval and over a longer period.
The difference in heel height was correlated with the difference in hoof angle, but heel height was
not added as a predictor. The fact that absolute difference in heel height added no more predictive
power to the function, combined with its size-dependent nature (in contrast to hoof angle), made
this justifiable.
Following our results, hoof width was not an appropriate discriminating factor for uneven feet, while
Ducro et al. (2009a) suggested that judges are relying on a narrow foot when scoring for unevenness
at studbook admissions. However, caution is needed in extrapolating their results, as the horses in
our study were classified by one clinician who possibly focused on other factors than the studbook
judges. On the other hand, it could be that observers in fact focus on the hoof spread (i.e. the
difference between hoof width at the bottom and top of the hoof) as described by Wilson et al.
(2009), rather than on the hoof width at the bottom of the hoof used in our study. Unfortunately this
data is not available for the current study, as this study is partly based on the data of a larger
previously initiated research project. Lastly, subtle differences could have been masked by the 3.7
mm measurement error.
Uneven footed horses, as well as even footed horses, showed differences in Pprox angle and in fetlock
angle between the forefeet. Previous reports demonstrated that an artificial heel elevation and a
subsequent increase in toe angle are associated with a more horizontal position of the proximal
phalanx (Denoix, 1985) and with a decrease in the dorsoflexion angle of the fetlock joint (Bushe et
al., 1988; Crevier-Denoix et al., 2001). In line with these reports, one might expect that horses with
uneven feet will show larger differences in fetlock angle and in Pprox angle between the forefeet than
horses with even feet.
The fact that not only uneven footed horses, but also even footed horses showed substantial
differences in Pprox angle and in fetlock angle could be evoked by corrective trimming techniques (e.g.
shortening of the toe of the LHA foot). This can give originally ‘uneven’ hooves an ‘even’ appearance
24
(and classification), as shortening of the toe leads to an increased hoof angle in the LHA foot
(Clayton, 1988; Clayton, 1990), thereby reducing the difference in hoof angle between the forefeet.
However, skeletal asymmetries of the limbs could still be present. To determine if this is a real issue,
horses need to be followed up after a trimming session.
Moreover, the angle measurements could have been affected by preferential weight-bearing during
standing. Although the limbs were positioned as square as possible, some horses showed a strong
preference for a particular standing posture, which might have influenced the limb loading.
The asymmetries in third metacarpal bone length and in proximal phalanx length did not discriminate
between horses with even feet and horses with uneven feet. If skeletal asymmetries are caused by
an asymmetrical loading pattern at foal age (Kroekenstoel et al., 2006; van Heel et al., 2006a), the
findings in the current study can be explained from two different perspectives. On the one hand, it is
possible that an asymmetrical loading pattern at juvenile age does not lead to asymmetries in third
metacarpal bone length or in proximal phalanx length. On the other hand, clinically relevant loading
asymmetries could have developed after the cessation of the length growth of the two bony
elements. For the radiographic closure times of the growth plates, values have been reported,
varying between 7.5 and 14 months for the proximal part of the proximal phalanx, and between 7
and 14 months for the distal part of the third metacarpal bone (Fretz et al., 1984; Koskinen and
Katila, 1997; Strand et al., 2007).
Apart from previously reported developmental aspects at foal age (Kroekenstoel et al., 2006; van
Heel et al., 2006a), (subclinical) lameness after that age could have played a role in the development
of uneven feet, since the mean ± s.d. age of the visually uneven footed riding horses in the current
study was 12 ± 6 years.
Further research could reveal if there are any changes in thickness or material properties of the third
metacarpal bone and proximal phalanx. Moreover, it would be interesting to study if unevenness of
the feet is associated with proximal limb asymmetries.
25
4.2 Relationship between unevenness and functional parameters
4.2.1
Longitudinal ground reaction force
Our finding that braking force and braking impulse were different between the forefeet of uneven
footed horses, could be associated with two mechanisms: the decreased braking impulse in the HHA
foot is compensated by (1) increased braking forces in the contralateral forefoot, or by (2) decreased
propulsive forces in the contralateral hindfoot. These effects have already been demonstrated in
lame horses (Clayton et al., 2000; Morris and Seeherman, 1987). Therefore, in horses with uneven
feet, the smaller peak braking force and braking impulse in the HHA foot compared to the LHA foot
could imply a subtle, visually undetectable lameness at trot. Parkes et al. (2009) have already
reported that the human ability to detect asymmetrical movement is limited, as movement
asymmetries below 25% remain undetectable to the observer. Furthermore, the larger braking
impulse in the LHA foot could indicate that the LHA foot was sliding more during ground contact
compared to the HHA foot. This can be tested in the future by comparing the slip distance between
the LHA and the HHA foot.
The hypothesis that the transition from braking to propulsion occurs later in the LHA foot compared
to the HHA foot of uneven footed horses was supported by the discriminant function classification
method and by the linear positive correlation between difference in hoof angle and the timing of the
transition. These findings can be associated with two mechanisms. Firstly, the later transition from
braking to propulsion in the LHA feet could be related to the prolonged breakover time of hooves
with a relatively long toe and a low hoof angle, as reported by Clayton (1990). It takes longer for the
center of mass to rotate over the flat footed limb, leading to a later onset of breakover and a later
transition from braking to propulsion. Secondly, horses with a low hoof angle show a more
pronounced toe-first landing (Clayton, 1990), which could lead to a later onset of complete hoof
stabilization and breakover. Indeed, a flatter hoof landing (the opposite of toe-first landing) results in
a shorter duration of events after first ground contact, with a higher vertical and horizontal loading
rate and a shorter braking phase (Gustås et al., 2001).
26
4.2.2
Vertical ground reaction force
Since our data were limited to visually non-lame horses at trot, we expected that the vertical forces
would not differ between the forefeet. Lameness can be detected by left-right asymmetries in peak
vertical forces, with the lame limb showing the lower peak force (Back et al., 2007; Clayton et al.,
2000; Morris and Seeherman, 1987; Weishaupt et al., 2006). In contrast to our expectations, the
vertical forces were significantly different between the forefeet of the uneven footed horses used in
our study, with values of 0.289 N/kg (VC) and 0.250 N/kg (DF). This was not the result of an altered
limb orientation, as the peak vertical forces occurred at the moment of minimal longitudinal forces in
both feet, which means that the angle of the peak resultant GRF vector was oriented perpendicular
to the ground. The reduction in the peak vertical force of the HHA foot (VC: 2.73%, DF: 2.30%) in our
study was lower than the reduction of 4% reported for a subtle visually detectable lameness
(Weishaupt et al., 2006). As with the fore-aft forces, this could imply an early, subclinical sign of
lameness developing in the HHA foot. This idea could be further supported by the fact that of the 21
uneven footed horses that were analyzed at trot, 6 were slightly lame in the HHA foot at walk (table
2.2).
The question remains, however, whether the vertical force distribution between the uneven feet in
the current study is related to an asymmetrical loading pattern without a pathological component or
to a subclinical lameness as a result of a pathology. If a pathological factor plays a role, this could
possibly be associated with the radiologically more lucent (osteoporotic) navicular bone with a more
pronounced (remodeled) dorsal flexor side in the HHA foot, as demonstrated by Bakker et al. (2012).
However, further clinical, biomechanical and radiological monitoring over time is needed for a better
understanding of (the existence and direction of) the link between lameness and uneven feet.
27
4.2.3
Stiffness
In contrast to the peak vertical forces, the vertical forces at the moment of peak vertical fetlock
displacement were not significantly different between the forefeet of horses with uneven feet. From
the higher, but similarly timed peak vertical force in the LHA foot compared to the HHA foot, one can
conclude that a force of the same magnitude (that is, a force at peak vertical fetlock displacement) is
reached earlier in the LHA foot. In other words, the peak vertical fetlock displacement is reached
earlier in the LHA foot, as depicted in figure 4.1. This, in combination with the larger vertical fetlock
displacement in the LHA foot, leads to a higher velocity of vertical fetlock displacement in the LHA
foot. This, in fact, could be the clinically observed asymmetry in fetlock movement in uneven footed
horses (pers. observ. Wim Back).
Figure 4.1 – Schematic representation of the timing of maximal
vertical fetlock displacement in the LHA foot and in the HHA foot of
uneven footed horses.
The graph shows that the timing of the peak vertical force is not different
(green dotted line), but the magnitude of the peak vertical force was
higher in the LHA foot compared to the HHA foot. Consequently, the force
at the moment of maximal vertical fetlock displacement occurs earlier in
the LHA foot (blue dotted line) compared to the HHA foot (red dotted line),
while the magnitude of the force at that point does not differ between the
feet (black dotted line).
All of the above-mentioned effects can be described using one variable, ‘stiffness’. The stiffness
calculated in our study was based on the previously described ‘effective vertical stiffness’ (Farley et
al., 1993; McMahon and Cheng, 1990), which is the ratio of the peak vertical force to the peak
vertical displacement of the center of mass during the stance phase. We used the peak vertical
displacement of the fetlock joint and the coinciding vertical force to calculate the stiffness, since
extension of this joint is an important factor in the shortening of the limb spring (McGuigan and
Wilson, 2003).
28
In our study, horses with uneven feet showed a less stiff limb spring in the LHA foot than in the HHA
foot. This is most likely caused by differences in the quality of the spring-like distal limb tissues;
especially of the tendo interosseus and the deep and superficial digital flexor muscles and tendons
(Dyce et al., 2009; McGuigan and Wilson, 2003). The more radiodens (compact) deep digital flexor
tendon in the HHA foot, as demonstrated by Bakker et al. (2012), could possibly be linked to the
higher stiffness of the limb found in our study. Differences in heel expansion could also play a role.
The differences in stiffness between the uneven forefeet are less likely the result of possible
differences in the moment arms around the distal limb joints due to the asymmetric foot
conformation, since stiffness was not significantly different between flat, medium and upright feet.
Although it is still unknown which of the distal limb structures could cause the asymmetry in
stiffness, we defined an objectively measurable parameter to quantify the clinically observed
differences in fetlock movement between the forefeet. Radiological and biochemical evaluation of
the distal limb tissues of uneven footed horses, with special attention to the suspensory apparatus
and the superficial and deep digital flexor tendons will add to the understanding of the etiology.
29
4.3 Relationship between individual foot conformation and
functional parameters
Individual foot conformation was less important for biomechanical characteristics than the
conformational differences between the forefeet, since none of the functional parameters were
associated with foot category or linearly correlated with absolute hoof angle.
Stance duration and the timing of the force peaks were not different between flat, medium or
upright feet, which supported the findings of previous studies (Chateau et al., 2004; Chateau et al.,
2006; Clayton, 1990; van Heel et al., 2006b; Wilson et al., 1998). This implies that stance duration
and other temporal characteristics are independent of the individual foot conformation and are
strictly controlled by the neuromuscular system. On the other hand, the fact that these temporal
variables did not differ between the foot categories could be caused by a between-horse variability in
speed.
As expected, the conformational categories showed no differences in vertical ground reaction force
and this was in line with the previously found unaltered peak vertical GRF after application of a 6°
heel wedge (Willemen et al., 1999).
The hypothesis that the transition from longitudinal braking to propulsive forces occurs earlier in
upright feet, while flat feet show a later transition, was rejected. Based upon the reported toe-first
landing in flat feet (Clayton, 1990), one might expect a prolonged braking phase in flatter feet
(Gustås et al., 2001). The fact that this idea was not supported by our findings, could indicate that the
different foot categories in the current study showed no differences in hoof landing pattern.
Moreover, the longer breakover duration in flat feet found in previous studies (Balch et al., 1994;
Clayton, 1988; Clayton, 1990), did not lead to an altered shape of the fore-aft force profile in the
current study. Unlike our study, most previous studies are based on artificially induced changes in
hoof angle. Changes in hoof angle within the animal rather than conformational differences in hoof
angle between horses may therefore be more influential in producing altered longitudinal force
patterns.
The conformation of the individual foot was not associated with the stiffness of the limb and the
vertical displacement of the fetlock. Results from previous studies on the extension of the fetlock
joint after the application of a heel wedge were conflicting. Willemen et al. (1999) and Chateau et al.
(2006) found no significant effect of a 6° heel wedge on the maximal fetlock extension at the trot,
which is in line with our findings. In contrast, Scheffer and Back (2001) demonstrated a significant
reduction in maximal fetlock extension after heel elevation with a 5° wedge at trot. Since our study
investigated vertical fetlock displacement instead of fetlock extension, a possible compensatory
effect of the interphalangeal joints on a reduced fetlock extension cannot be ruled out. This seems
unlikely, however, since Chateau et al. (2006) showed that a 6° heel wedge caused an increase in
maximal flexion and a decrease in maximal extension of the proximal and distal interphalangeal
joints at the trot .
30
4.4 Conclusion
This study showed that unevenness of the feet can be best determined by the absolute differences in
hoof angle, although it seems difficult to objectively define a visually recognized uneven foot
conformation with high accuracy. The conformational differences between the forefeet seem to be
more important for loading characteristics than the individual foot conformation. The recorded
differences in vertical force between the uneven forefeet could in fact imply an early, subclinical sign
of lameness developing in the steeper foot, as these kinetic differences yet appeared even smaller
than those reported for a subtle lameness when becoming clinically evident.
31
4.5 Limitations and recommendations for future research
Research on the link between conformation and functionality in vivo is subjected to a combination of
complicating (environmental) factors, and controlling these factors is a challenging task. The present
study comprises the first steps towards a better understanding of the biomechanical aspects of an
uneven foot conformation. However, future research is necessary to establish a better understanding
of the clinical relevance of our findings. In the next part, the limitations of our study will be
presented, followed by recommendations for future research.
For logistic reasons, no standardized shoeing or trimming protocols were used in our study, which
could have influenced our results. Toe modifications could have distorted the classification
‘even/uneven’. By shortening the toe of the LHA foot of an originally uneven footed horse, the
difference in hoof angle between the forefeet can be reduced. In this way, feet could have been
classified as even, while still having skeletal asymmetries.
Moreover, the time between farrier treatment and the experimental measurements varied between
the horses. A previous study demonstrated that the moment on the distal interphalangeal joint
decreased more in the LHA foot than in the HHA foot during an 8-week shoeing interval, whereas the
decrease in hoof angle over time is not significantly different between the forefeet (Moleman et al.,
2006). The variation in time between farrier treatment and the measurements could therefore have
obscured the coherence between difference in hoof angle on the one hand, and the difference in
bone angles on the other. This, in turn, might have distorted the classification ‘even/uneven’ and the
functional parameters in the analyses of the individual foot. To determine if the time between
shoeing and measuring is of influence on foot classification and on functional parameters, horses
need to be followed up after a trimming session.
Since laterality is associated with biomechanical asymmetries (Grzimek, 1949; McGreevy and Rogers,
2005; Meij and Meij, 1980; Murphy et al., 2005; van Heel et al., 2010) and with uneven feet (van Heel
et al., 2010)(van Heel et al., 2010), further research could be conducted to determine the relative
influence of unevenness and laterality on functional asymmetries at the trot.
Other recommendations for further research include the evaluation of compensation mechanisms in
the hind limbs and the effects of corrective trimming and shoeing. To obtain more insight into the
proposed asymmetrical tissue properties, further biochemical and radiological research on distal limb
tissues should be performed. To further explore the differences in limb stiffness between the
forefeet, special attention must be paid to the tendo interosseus, to the superficial and deep digital
flexor tendons and to the fetlock joint. Building on the variations in shape of the coffin bone found by
Dyson et al. (2011), additional research could focus on the correlation between the differences in
hoof shape between the forefeet and the differences in position and morphology of the coffin bone.
For a better understanding of the link between lameness and uneven feet, and to evaluate a possible
causality, a follow-up study should be conducted on functional parameters of a large horse
population. Furthermore, radiological changes, especially of the suspensory apparatus and the
podotrochlear apparatus, should be monitored over time. Scoring for unevenness and lameness
should be performed by multiple observers to establish objective threshold values for unevenness
and for the development of lameness.
32
Acknowledgements
This page is made use of in order to convey appreciation and indebtedness to everyone who
contributed to the completion of my thesis.
On this occasion I wish to include dr. Sandra Nauwelaerts, for her systematic professional guidance.
Your patience, clear explanation and commitment were gratefully appraised. I would like to express
my very great appreciation for the huge amount of time and energy you invested in the assistance.
Your skills and knowledge have been of great help.
I am grateful for the professional and enthusiastic guidance of dr. Wim Back. His creative and
inspiring input is only matched by his clinical experience. I would like to thank him for scoring the
horses; even during the weekend.
I would wish to acknowledge my gratitude to dr. Claudia Wolschrijn, whose down-to-earth approach
and realistic view on the subject greatly benefited this thesis. I thank her for sharing her great
knowledge and her guidance on the reporting.
I would like to offer my sincere gratitude to dr. Sarah Jane Hobbs, for her excellent guidance during
the experiments. She has offered much help throughout the data processing. I also would like to
thank her for providing me with helpful answers and insightful feedback regarding the reporting.
Special thanks go to Sophie Bool, for helping with the experiments, for bringing in her own horse and
her personal commitment.
Hans Vernooij provided me with very valuable statistical advice, for which I would like to thank him.
The horses, provided by their owners, are at the heart of my research. Therefore, I am indebted to
the horse owners.
Other thanks go to Harry’s Horse and De Paardendrogist, for providing the sponsorship.
The advices and continuous support of my family are greatly valued. I would like to offer my
profound gratitude to:
Yoran Wiggers, for his linguistic assistance and advice;
Chaïlja Wiggers, for putting me wise in SPSS;
Yara Wiggers, for always lending a sympathetic ear;
my father, Benno Wiggers, for his encouragement throughout;
my mother, Monique Wiggers, who unfortunately cannot be with us anymore, but who endowed me
with her endless perseverance and passed her passion for horses on to me.
In concluding this page, I would like to thank Xanne Rooijers for her unconditional love and aid during
the good and bad times. Xanne, besides all the practical work you have done, I am most thankful for
the happiness we get to share in our lives.
33
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