Objective—To describe architectural changes along
the dorsal laminar interface of the equine foot.
Sample Population—6 macroscopically normal
forefeet obtained from 6 equine cadavers.
Procedure—Histologic sections of 8 evenly spaced,
proximal to distal, samples of the dorsal laminar interface
were photographed, digitized, and examined for
differences in architecture. Laminar depth; secondary
laminar density; number and consistency of bifurcations
occurring within the secondary laminae, and
areas composed of primary dermal lamina, primary
epidermal lamina, and secondary laminar interface
were recorded. Data were examined to test for differences
in architecture associated with the proximal to
distal positioning of the sample.
Results—With exception of the areas of the primary
epidermal and primary dermal lamina, all measured
variables were significantly different between the
proximal and distal regions of the dorsal laminar interface.
Changes included increases in laminar depth
and the secondary laminar density. Bifurcation of secondary
laminae principally occurred proximally and
had an increased depth of bifurcation distally. The secondary
laminar dermal-epidermal interface had a
109% increase in area between the most proximal
and distal sections.
Conclusions and Clinical Relevance—Results of
this study indicate that the interface normally contributes
a substantial volume of dermal components
to the internal surface of the wall. These data also
indicate that 2 distinct mechanisms (ie, bifurcation of
secondary laminae and an increase in the length of
secondary laminae) contribute to changes in the architecture
of the laminar interface, which allows for the
hypothesis that the normal laminar interface is capable
of responding to mechanical load. (Am J Vet Res 2005;66:277–283)
Objective—To evaluate the effect of prolonged water
exposure on tissue mass and solutes of outer and
inner layers of the stratum medium, sole, frog, and
the stratum medium (SMZA) zona alba layer of horses'
Specimen Population—10 hooves from 10 horses
without foot abnormalities.
Procedure—Hoof wall tissue specimens were
obtained and immersed for 10 days in distilled deionized
water. Serial changes in mass were recorded during
the immersion period. Subsequently, osmolarity
and Na+, K+, Cl–, and protein concentrations of the
immersion solution were quantified.
Results—Fully cornified outer hoof wall, sole, and
frog epidermal structures increased in mass, whereas
the SMZA lost mass when immersed in water. All
hoof structures had a variable loss of crystalloids during
immersion, but none of the specimens lost proteins.
The frog epidermis was distinct in that total
solute lost during immersion could not be ascribed to
Na+, K+, and Cl–.
Conclusions and Clinical Relevance—Data support
a 2-compartment model for the fully cornified outer
stratum medium, frog, and sole that permits the
exchange of crystalloids, but not proteins, across the
cell membrane and infers that topical agents containing
proteins cannot benefit the hoof. The unique
osmotic behavior of the SMZA relative to other hoof
structures suggests the hypothesis that it is composed
of transitional epithelial cells. The solutes lost
from frog epithelium are interpreted to reflect its
unique lipid composition. (Am J Vet Res
Objective—To determine whether a unique dihydropyridine
(BAY TG 1000) would be beneficial in preventing
laminitis in horses.
Animals—16 clinically normal adult horses.
Procedure—8 pairs of horses were used in a controlled
double-blind study, using sex- and agematched
horses randomly assigned to treatment or
control groups. Horses were subjected to carbohydrate
overload to induce laminitis. Treated horses
were administered BAY TG 1000 (30 mg/kg, PO, q
24 h) for 3 days. Hoof wall surface temperature
(HWST) and lameness were recorded at 4-hour
intervals. The HWST was adjusted on the basis of
time of onset of lameness and evaluated, using a
repeated-measures ANOVA. Lameness 8 hours
after onset and clinical status 72 hours after onset
of lameness were evaluated, using Mann-Whitney
Results—Analysis revealed that BAY TG 1000 did not
decrease the incidence of lameness but significantly
ameliorated prodromal hypothermia, lessened the
severity of lameness 8 hours after onset of lameness,
and improved the clinical status of horses 72 hours
after onset of lameness.
Conclusion and Clinical Relevance—Results support
the conclusion that BAY TG 1000 was protective
when used in prevention of laminitis. The drug
decreased severity and improved clinical status
(recovery) of induced lameness, which was interpreted
to mean that the drug's actions were on mechanisms
important but secondary to primary causal
mechanisms of laminitis. Therefore, drugs that
enhance digital perfusion via alteration of rheologic
activity may have potential use in the prevention and
management of laminitis in horses. (Am J Vet Res
Objective—To evaluate the clinical efficacy of topically
administered glyceryl trinitrate (GTN) for inducing
digital submural vasodilation in clinically normal
Animals—7 adult horses without foot abnormalities.
Procedures—A concurrent-control crossover design
was used to determine whether topical application of
GTN ointment for prevention or treatment of laminitis
would result in a detectable increase in digital perfusion.
Heat-acclimated horses instumented for detection
of wall surface temperature (HWST), mean systemic
pressure, and heart rate were used. Horses
were exposed to cold to induce digital vasoconstriction
and treated with GTN in an attempt to induce digital
Results—Application of GTN failed to induce an
increase in digital submural perfusion but did induce a
mild decrease in mean systemic pressure.
Conclusionss and Clinical Relevance—Topical application
of 60 mg of GTN as a 2% ointment on the
skin over the major vasculature in the region of the
proximal interphalangeal joint (pastern) of horses
was not effective in significantly increasing digital
perfusion. A decrease in mean systemic pressure
following treatment was observed, implying that the
drug was absorbed. Use of GTN may result in a
decrease in digital submural perfusion secondary to
induction of peripheral constriction or a decrease in
digital perfusion pressure. (Am J Vet Res
Objective—To evaluate the short-term effects of 4
therapeutic shoeing systems on lameness and voluntary
limb-load distribution in horses with chronic
Animals—10 horses with chronic laminitis.
Procedures—A clinical trial was conducted that used
a concurrent control, crossover design to evaluate
the relative effectiveness of a standard flat shoe,
fullered egg-bar shoe, heart-bar shoe, and modified
equine digital support system to alleviate chronic
lameness in horses. Therapeutic success was
assessed during a 7-day period by use of subjective
(Obel grade and clinical score) and objective (forceplate
Results—Comparison of pretreatment and intertreatment
control data indicated that disease status of the
horses did not change during the course of the study.
None of the therapeutic shoeing treatments used
resulted in a significant change in severity of lameness.
Conclusions and Clinical Relevance—Results were
interpreted to imply that substantial clinical improvement
should not be expected during the first 7 days
after therapeutic shoeing for the specific shoes tested
in this study. On the basis of our results, we
hypothesize that when used as the lone indicator of
therapeutic success, severity of lameness may not be
a valid indicator. (Am J Vet Res 2002;63:1629–1633)
Objective—To determine whether solar load distribution
pattern on a solid nondeformable ground surface is
the product of contact erosion and is the mirror image
of load distribution on a deformable surface in horses.
Animals—30 clinically normal horses.
Procedures—Solar load distribution was compared
among 25 clinically normal horses during quasistatic
loading on a solid nondeformable surface and on a
highly deformable surface. Changes in solar load distribution
patterns were evaluated in 5 previously pasture-
maintained horses housed on a flat nondeformable
surface. Changes in solar load distribution
created by traditional trimming and shoeing were
Results—Unshod untrimmed horses had a 4-point
(12/25, 48%) or a 3-point (13/25, 52%) wall load distribution
pattern on a flat solid surface. Load distribution on
a deformable ground surface was principally solar and
located transversely across the central region of the
foot. Ground surface contact areas on solid (24.2 ± 8.62
cm2) and deformable (69.4 ± 22.55 cm2) surfaces were
significantly different. Maintaining unshod horses on a
flat nondeformable surface resulted in a loss of the 3-
and 4-point loading pattern and an increase in ground
surface contact area (17.9 ± 2.77 to 39.9 ± 12.77 cm2).
Trimming increased ground surface contact area (24.2 ±
8.60 to 45.7 ± 14.89 cm2).
Conclusion and Clinical Relevance—In horses, the
solar surface is the primary weight-loading surface,
and deformability of ground surface may have a role
in foot expansion during loading. Increased surface
area induced by loading on deformable surfaces, trimming,
and shoeing protects the foot. (Am J Vet Res
Objective—To evaluate the use of hoof wall surface
temperature (HWST) as an indirect indicator of digital
perfusion and to describe HWST patterns during the
prodromal and acute phases of carbohydrate-induced
laminitis in horses.
Animals—30 adult horses without foot abnormalities.
Procedures—Three experiments were performed. In
the first, HWST was measured in 2 groups of horses
acclimatized to hot (n = 6), or cold (6) environments
and exposed to cold (15 C) ambient temperature. In
the second experiment, HWST were measured in
both forefeet of 6 horses before and after application
of a tourniquet to 1 forefoot to induce vascular occlusion.
In the third experiment, HWST were recorded in
12 horses before and during the prodromal and acute
phases of carbohydrate-induced laminitis.
Results—Mean HWST of hot-acclimatized cold-challenged
horses was significantly less than that of cold-acclimatized
cold-challenged horses at all times.
Transient episodes of high HWST were observed during
prolonged cold-induced vasoconstriction. Hoof
wall surface temperature significantly decreased during
arterial occlusion and increased during reperfusion.
Digital hypothermia was observed during the
prodromal phase of carbohydrate-induced laminitis.
Conclusions and Clinical Relevance—Determination
of HWST is a valid technique to evaluate digital
perfusion under appropriate controlled conditions in
horses. Digital hypothermia detected during the prodromal
phase of laminitis is consistent with decreased
digital vascular perfusion or metabolic activity. If administered
to horses during the prodromal phase, agents
that enhance digital perfusion may prevent development
of laminitis. (Am J Vet Res 2001; 62:1167–1172)
Objective—To determine whether the bending modulus
and yield strength of the outer stratum medium
(SM) differed from those of the SM zona alba (SMZA)
and to what degree they differed. In addition, a comparison
was made among our values and values
Sample Population—10 normal equine feet.
Procedure—A 3-point bending technique was used
to determine the bending modulus and yield strength
of the outer SM and SMZA. Efforts were made to
minimize biological and technical factors that could
influence the bending modulus.
Results—Bending modulus of the outer SM was
(mean ± SD) 187.6 ± 41.3 MPa, whereas mean value
for the SMZA was 98.2 ± 36.8 MPa. Mean yield
strength was 19.4 ± 2.6 MPa for the outer SM and
5.6 ± 1.7 MPa for the SMZA. Values for bending modulus
and yield strength differed significantly between
the outer SM and SMZA. Significant differences were
not detected when the outer SM was loaded in bending
from the outer or inner surface.
Conclusions and Clinical Relevance—Potentially,
the SMZA could serve as a mechanical buffer zone
between the rigid hoof wall and bone and laminar tissues.
This buffer zone potentially assists the feet of
horses in transmitting a load through the tissues and
prevents the most susceptible tissues from becoming
damaged. More consistency among tissue selection,
preparation, and testing protocols must be
attained before an accurate 3-dimensional finite-element
model of an equine foot can be constructed.
(Am J Vet Res 2001;62:745–751)
Objective—To investigate the effects of ketamine hydrochloride on the analgesic effects of tramadol hydrochloride in horses with signs of pain associated with naturally occurring chronic laminitis.
Animals—15 client-owned adult horses with chronic laminitis.
Procedures—Each horse received tramadol alone or tramadol and ketamine in a randomized, crossover study (≥ 2 months between treatments). Tramadol (5 mg/kg) was administered orally every 12 hours for 1 week. When appropriate, ketamine (0.6 mg/kg/h) was administered IV for 6 hours on each of the first 3 days of tramadol administration. Noninvasive systemic blood pressure values, heart and respiratory rates, intestinal sounds, forelimb load and off-loading frequency (determined via force plate system), and plasma tumor necrosis factor-α and thromboxane B2 concentrations were assessed before (baseline) during (7 days) and after (3 days) each treatment.
Results—Compared with baseline data, arterial blood pressure decreased significantly both during and after tramadol-ketamine treatment but not with tramadol alone. Forelimb off-loading frequency significantly decreased during the first 3 days of treatment with tramadol only, returning to baseline frequency thereafter. The addition of ketamine to tramadol treatment reduced off-loading frequency both during and after treatment. Forelimb load did not change with tramadol alone but increased with tramadol-ketamine treatment. Plasma concentrations of tumor necrosis factor-α and thromboxane B2 were significantly reduced with tramadol-ketamine treatment but not with tramadol alone.
Conclusions and Clinical Relevance—In horses with chronic laminitis, tramadol administration induced limited analgesia, but this effect was significantly enhanced by administration of subanesthetic doses of ketamine.
Objective—To describe submural histopathologic
changes attributable to peracute laminitis in horses.
Animals—20 adult horses.
Procedure—A concurrent-control design was used to
compare laminar lesions in 10 horses subjected to
carbohydrate-induced laminitis with laminar characteristics
of 10 sex- and aged-matched control horses
with normal feet. Horses in the treatment group were
administered an overload of carbohydrate. Tissues
were obtained by biopsy 4 to 8 hours after onset of
lameness or 72 hours after administration of the carbohydrate
overload when lameness did not develop.
Sections were stained with H&E, Masson's trichrome,
and periodic acid-Schiff stains. Histopathologic changes
were analyzed to detect differences between groups
and to correlate epidermal changes with severity and
duration of lameness.
Results—Analysis indicated that dermal and epidermal
lesions were evident despite lack of visible separation
of the epidermal basement membrane, can be
found in horses without detectable lameness, and
were nonspecific and progressive following onset of
lameness. Furthermore, severity and location of
lesions were associated with severity and duration of
Conclusion and Clinical Relevance—These observations
are consistent with the concept that separation
of the laminar epithelial basement membrane is
a delayed step in the pathogenesis of acute laminitis,
digital vascular hypoperfusion is an underlying cause
for laminitis, and the potential for repeated episodes
of subclinical laminitis may underlie the development
of structural and mechanical changes consistent with
chronic laminitis despite lack of clinical signs of acute
laminitis. (Am J Vet Res 2003;64:829–834)