Objective—To determine the mechanism that enables horses to partially counteract the shift of the center of pressure under the hoof induced by changes in hoof morphology attributable to growth and wear during a shoeing interval.
Animals—18 clinically sound Warmblood horses.
Procedures—Horses were evaluated 2 days and 8 weeks after shoeing during trotting on a track containing pressure-force measuring plates and by use of a synchronous infrared gait analysis system set at a frequency of 240 Hz. All feet were trimmed toward straight alignment of the proximal, middle, and distal phalanges and shod with standard flat shoes.
Results—Temporal characteristics such as stance time and the time between heel lift and toe off (ie, breakover duration) did not change significantly as a result of shoeing interval. Protraction and retraction angles of the limbs did not change. Compensation was achieved through an increase in the dorsal angle of the metacarpohalangeal or metarsophalangeal (fetlock) joint and a concomitant decrease of the dorsal angle of the hoof wall and fetlock. There was an additional compensatory mechanism in the hind limbs during the landing phase.
Conclusions and Clinical Relevance—Horses compensate for changes in hoof morphology that develop during an 8-week shoeing interval such that they are able to maintain their neuromuscular pattern of movement. The compensation consists of slight alterations in the angles between the distal segments of the limb. Insight into natural compensation mechanisms for hoof imbalance will aid in the understanding and treatment of pathologic conditions in horses.
Objective—To evaluate a modified digital imaging
technique for quantitative assessment of the grade of
osteoarthritis across the proximal articular surface of
the first phalanx in horses.
Sample Population—6 metacarpophalangeal (fetlock)
joint specimens from 6 horses with various
stages of osteoarthritis.
Procedure—First phalanx specimens, together with 4
gray scale reference calibration targets, were positioned
in a bath with the proximal articular cartilage surface
submerged in saline (0.9% NaCl) solution. Digital
images were obtained from the articular surface before
and after staining with Indian ink. Computer-controlled
gray level analysis of the nonstained and Indian ink-stained
cartilage surfaces and gray scale reference calibration
targets was performed by use of the mean
pixel value (based on 255-gray scale). An increase in
the mean pixel value after staining was used to calculate
the cartilage degeneration index (CDI).
Results—The CDI of the proximal articular cartilage
surface of the first phalanx specimens ranged from
9.2 ± 5.7 (early stage osteoarthritis) to 41.5 ± 3.6%
(late stage osteoarthritis). The effect of repeating the
measurement 6 times in nonstained (including repositioning)
and stained specimens (including repositioning
and restaining) was not significant. Up to 10
measurements of nonstained specimens could be
made without refreshing the bath solution. In stained
specimens, mean gray level increased significantly
after the sixth measurement.
Conclusion and Clinical Relevance—The modified
digital imaging technique allowed quantitative assessment
of cartilage degeneration across the articular
cartilage surface. The CDI is the first quantitative measure
for osteoarthritis-induced cartilage degeneration
over an entire joint surface in horses. (Am J Vet Res
Objective—To determine the relationship between the output of an electrical treatment device and the effective field strength in the superficial digital flexor tendon of horses.
Sample Population—Cadaver horse forelimbs without visible defects (n = 8) and 1 live pony.
Procedure—Microcurrents were generated by a microcurrent electrical therapy device and applied in proximodistal, dorsopalmar, and mediolateral directions in the entire forelimbs, dissected tendons, and the pony with various output settings. Corresponding field strengths in the tendons were measured.
Results—A linear relationship was detected between current and field strength in all conditions and in all 3 directions. In dissected tendons, significant differences were detected among all 3 directions, with highest field strength in the proximodistal direction and lowest in the dorsopalmar direction. In the entire forelimbs, field strength in the proximodistal direction was significantly lower than in the mediolateral direction. Results in the pony were similar to those in the entire forelimbs.
Conclusions and Clinical Relevance—Electrode placement significantly affected field strength in the target tissue. Many surrounding structures caused considerable reduction of field strength in the target tissue. These factors should be taken into account when establishing protocols for electrical current–based therapeutic devices if these devices are proven clinically effective.
Objective—To determine effects of microcurrent electrical tissue stimulation (METS) on equine tenocytes cultured from the superficial digital flexor tendon (SDFT).
Sample Population—SDFTs were collected from 20 horses at slaughter.
Procedure—Tenocytes were isolated following outgrowth from explants and grown in 48-well plates. Four methods of delivering current to the tenocytes with a METS device were tested. Once the optimal method was selected, current consisting of 0 (negative control), 0.05, 0.1, 0.5, 1.0, or 1.5 mA was applied to cells (8 wells/current intensity) once daily for 8 minutes. Cells were treated for 1, 2, or 3 days. Cell proliferation, DNA content, protein content, and apoptosis rate were determined.
Results—Application of microcurrent of moderate intensity increased cell proliferation and DNA content, with greater increases with multiple versus single application. Application of microcurrent of moderate intensity once or twice increased protein content, but application 3 times decreased protein content. Application of current a single time did not significantly alter apoptosis rate; however, application twice or 3 times resulted in significant increases in apoptosis rate, and there were significant linear (second order) correlations between current intensity and apoptosis rate when current was applied twice or 3 times.
Conclusions and Clinical Relevance—Results of the present study indicate that microcurrent affects the behavior of equine tenocytes in culture, but that effects may be negative or positive depending on current intensity and number of applications. Therefore, results are far from conclusive with respect to the suitability of using METS to promote tendon healing in horses.
Objective—To describe spontaneous locomotion activity of foals kept under various management conditions and assess the suitability of global positioning system (GPS) technology for recording foal activity.
Procedures—During the foals' first 4 months of life, 921 observation periods (15 minutes each) were collected and analyzed for locomotion activities. The GPS system was evaluated by simultaneously carrying out field observations with a handheld computer.
Results—Foals spent 0.5% of total observed time cantering, 0.2% trotting, 10.7% walking, 32.0% grazing, 34.8% standing, and 21.6% lying down. Total observed daytime workload (velocity × distance) in the first month was approximately twice that in the following months. Locomotion activity decreased with increasing age. Colts had more activity than fillies in certain periods, and foals that were stabled for some portion of the day had compensatory locomotion activity, which was probably insufficient to reach the level of foals kept continually outside. The GPS recordings and handheld-computer observations were strongly correlated for canter, trot, and walk and moderately correlated for standing and lying. Correlation for grazing was low.
Conclusions and Clinical Relevance—Results indicated that domestically managed foals, when kept 24 h/d at pasture, will exercise at a level comparable with feral foals. High workload during the first month of life might be important for conditioning the musculoskeletal system. The GPS technique accurately quantified canter, trot, and walk activities; less accurately indexed resting; and was unsuitable for grazing because of the wide array of velocities used while foraging.
Objective—To evaluate effectiveness of computerized
discrimination between structure-related and
non–structure-related echoes in ultrasonographic
images for quantitative evaluation of tendon structural
integrity in horses.
Sample Population—4 superficial digital flexor tendons
(2 damaged tendons, 2 normal tendons).
Procedure—Transverse ultrasonographic images that
precisely matched histologic sections were obtained
in fixed steps along the long axis of each tendon.
Distribution, intensity, and delineation of structurerelated
echoes, quantitatively expressed as the correlation
ratio and steadiness ratio , were compared with
histologic findings in tissue that was normal or had
necrosis, early granulation, late granulation, early
fibrosis, or inferior repair.
Results—In normal tendon, the even distribution of
structure-related echoes with high intensity and sharp
delineation yielded high correlation ratio and steadiness
ratio. In areas of necrosis, collapsed endotendon
septa yielded solid but blurred structure-related
echoes (high correlation ration and low steadiness
ratio). In early granulation tissue, complete lack of
organization caused zero values for both ratios. In late
granulation tissue, reorganization and swollen endotendon
septa yielded poorly delineated structurerelated
echoes (high correlation ratio, low steadiness
ratio). In early fibrosis, rearrangement of bundles
resulted in normal correlation ration and slightly low
steadiness ratio. In inferior repair, the almost complete
lack of structural reorganization resulted in heterogeneous
poorly delineated low-intensity echoes
(low correlation ratio and steadiness ratio).
Conclusions and Clinical Relevance—The combination
of correlation ratio and steadiness ratio accurately
reflects histopathologic findings, making computerized
correlation of ultrasonographic images an efficient
tool for quantitative evaluation of tendon structural
integrity. (Am J Vet Res 2001;62:1159–1166)
Objective—To describe a method of computerized
ultrasonographic tissue characterization that includes
structures below the size limits of resolution in equine
superficial digital flexor tendons.
Sample Population—2 damaged and 2 structurally
normal superficial digital flexor tendons.
Procedure—Transverse ultrasonographic images were
collected along the tendon long axis. Stability of echo
pattern was quantified by means of variation in gray levels
of each pixel in contiguous images and expressed
as correlation, entropy, and waviness ratios.
Results—Normal young and normal old tissues were
characterized by high correlation and low entropy and
waviness ratios. In necrotic tissue, collapsed intratendinous
septa resulted in high correlation, moderate
entropy, and high waviness ratios. In early granulation tissue,
complete lack of bundle formation resulted in values
of zero for correlation and waviness ratios; loose
connective tissue matrix resulted in a high entropy ratio.
In late granulation tissue, formation of new bundles
resulted in a high correlation ratio; swollen intratendinous
septa and incomplete organization of connective
tissue matrix were reflected in high entropy and waviness
ratios. In early fibrotic tissue, rearrangement of tendon
bundles resulted in a correlation ratio within reference
range and a slight increase in the waviness ratio; an
increase in cellularity and lack of fibrillar arrangement led
to an increase in the entropy ratio. In late fibrotic and scar
tissues, inferior quality of repair with almost complete
lack of organization was reflected in low to moderate
correlation, low waviness, and high entropy ratios.
Conclusions and Clinical Relevance—Stability of
echo patterns accurately reflects homogeneity of tendons
in horses. (Am J Vet Res 2003;64:366–375)
Objective—To assess the effects of age and joint disease
on hydroxyproline and glycosaminoglycan (GAG)
concentrations in synovial fluid from the metacarpophalangeal
joint of horses and evaluate the association
of those concentrations with severity of
osteoarthritis and general matrix metalloproteinase
Sample Population—Synovial fluid was collected
from the metacarpophalangeal joints of foals at birth
(n = 10), 5-month-old foals (10), 11-month-old foals (5),
and adult horses (73).
Procedure—Hydroxyproline and GAG concentrations
were determined in synovial fluid samples. The severity
of osteoarthritis in adult joints was quantified by use
of a cartilage degeneration index (CDI) and assessment
of general MMP-activity via a fluorogenic assay.
Results—Hydroxyproline and GAG concentrations in
synovial fluid were highest in neonates and
decreased with age. Concentrations reached a
plateau in adults by 4 years and remained constant in
healthy joints. In synovial fluid from osteoarthritic
joints, hydroxyproline and GAG concentrations were
not increased, compared with unaffected joints, but
hydroxyproline were significantly correlated with the
CDI and general MMP activity. There was no significant
correlation between GAG concentration and CDI
value or MMP activity.
Conclusions and Clinical Relevance—Changes in
hydroxyproline concentration in synovial fluid
appeared to indicate damage to collagen of the articular
cartilage. In joints with osteoarthritis, the lack of
high GAG concentration in synovial fluid and the
absence of a significant correlation between GAG
concentration and CDI values or MMP activity may
severely limit the usefulness of this marker for monitoring
equine joint disease (J Am Vet Med Assoc 2004;65:296–302)
Objective—To investigate the effects of early training
for jumping by comparing the jumping technique of
horses that had received early training with that of
horses raised conventionally.
Animals—40 Dutch Warmblood horses.
Procedure—The horses were analyzed kinematically
during free jumping at 6 months of age.
Subsequently, they were allocated into a control
group that was raised conventionally and an experimental
group that received 30 months of early training
starting at 6 months of age. At 4 years of age,
after a period of rest in pasture and a short period of
training with a rider, both groups were analyzed kinematically
during free jumping. Subsequently, both
groups started a 1-year intensive training for jumping,
and at 5 years of age, they were again analyzed kinematically
during free jumping. In addition, the horses
competed in a puissance competition to test maximal
Results—Whereas there were no differences in
jumping technique between experimental and control
horses at 6 months of age, at 4 years, the experimental
horses jumped in a more effective manner
than the control horses; they raised their center of
gravity less yet cleared more fences successfully than
the control horses. However, at 5 years of age, these
differences were not detected. Furthermore, the
experimental horses did not perform better than the
control horses in the puissance competition.
Conclusions and Clinical Relevance—Specific training
for jumping of horses at an early age is unnecessary
because the effects on jumping technique and
jumping capacity are not permanent. (Am J Vet Res 2005;66:418–424)
Objective—To quantify and compare biochemical
characteristics of the extracellular matrix (ECM) of
specimens harvested from tensional and compressive
regions of the superficial digital flexor tendon
(SDFT) of horses in age classes that include neonates
to mature horses.
Sample Population—Tendon specimens were collected
on postmortem examination from 40 juvenile
horses (0, 5, 12, and 36 months old) without macroscopically
visible signs of tendonitis.
Procedure—Central core specimens of the SDFT
were obtained with a 4-mm-diameter biopsy punch
from 2 loaded sites, the central part of the midmetacarpal
region and the central part of the midsesamoid
region. Biochemical characteristics of the
collagenous ECM content (ie, collagen, hydroxylysylpyridinoline
crosslink, and pentosidine crosslink
concentrations and percentage of degraded collagen)
and noncollagenous ECM content (percentage of
water and glycosaminoglycans, DNA, and hyaluronic
acid concentrations) were measured.
Results—The biochemical composition of equine
SDFT was not homogeneous at birth with respect to
DNA, glycosaminoglycans, and pentosidine concentrations.
For most biochemical variables, the amounts
present at birth were dissimilar to those found in
mature horses. Fast and substantial changes in all
components of the matrix occurred in the period of
growth and development after birth.
Conclusions and Clinical Relevance—Unlike cartilage,
tendon tissue is not biochemically blank (ie, homogeneous)
at birth. However, a process of functional adaptation
occurs during maturation that changes the composition
of equine SDFT from birth to maturity.
Understanding of the maturation process of the juvenile
equine SDFT may be useful in developing exercise programs
that minimize tendon injuries later in life that
result from overuse. (Am J Vet Res 2005;66:1623–1629)