Objective—To characterize the texture, mineralogic
features, and chemical features of enteroliths
obtained from horses.
Sample Population—Enteroliths from 13 horses
Procedure—Enteroliths were harvested from 13
horses that underwent ventral midline celiotomy for
treatment of colic or necropsy because of colonic
obstruction and rupture caused by enteroliths. Dietary
and environmental history were determined via questionnaires
or evaluation of medical records. In 7 horses
that underwent surgical treatment for enterolithiasis,
samples of colonic contents were obtained via an
enterotomy in the pelvic flexure. Colonic concentrations
of magnesium (Mg), phosphorus (P), sulfur (S),
sodium (Na), calcium (Ca), and potassium (K) were
determined. Enteroliths were analyzed via electron
microprobe analysis and X-ray diffraction.
Results—Enteroliths varied widely regarding degree
of porosity, presence and distribution of radiating texture,
and composition and size of the central nidus. A
distinct concentric banding was identifiable in all
enteroliths. Struvite was the predominant component
of all enteroliths, although Mg vivianite was identified
in 5 enteroliths, and there were variable quantities of
Na, S, K, and Ca in the struvite within enteroliths.
Despite an abundance of Ca in colonic fluids, Mgphosphate
minerals were preferentially formed, compared
with Ca-phosphates (apatite), in equine
Conclusions and Clinical Relevance—Enteroliths
comprise 2 major Mg phosphates: struvite and Mg
vivianite. There is wide variability in macrotexture and
ionic concentrations between and within enteroliths.
(Am J Vet Res 2001;62:350–358)
Objectives—To determine the in vitro effect of
prostaglandin E2 (PGE2), PGF2α, PGI2; and nonsteroidal
anti-inflammatory drugs (NSAID; ie, flunixin
meglumine, ketoprofen, carprofen, and phenylbutazone)
on contractile activity of the equine dorsal
colon, ventral colon, and pelvic flexure circular and
longitudinal smooth muscle.
Animals—26 healthy horses.
Procedure—Tissue collected from the ventral colon,
dorsal colon, and pelvic flexure was cut into strips and
mounted in a tissue bath system where contractile
strength was determined. Incremental doses of
PGE2, PGF2α, PGI2, flunixin meglumine, carprofen,
ketoprofen, and phenylbutazone were added to the
baths, and the contractile activity was recorded for
each location and orientation of smooth muscle.
Results—In substance P-stimulated tissues, PGE2
and PGF2α enhanced contractility in the longitudinal
smooth muscle with a decrease or no effect on circular
smooth muscle activity. Prostaglandin I2 inhibited
the circular smooth muscle response with no effect
on the longitudinal muscle. The activity of NSAID was
predominantly inhibitory regardless of location or
Conclusions and Clinical Relevance—In the equine
large intestine, exogenous prostaglandins had a variable
effect on contractile activity, depending on the
location in the colon and orientation of the smooth
muscle. The administration of NSAID inhibited contractility,
with flunixin meglumine generally inducing
the most profound inhibition relative to the other
NSAID evaluated in substance P-stimulated smooth
muscle of the large intestine. The results of this study
indicate that prolonged use of NSAID may potentially
predispose horses to develop gastrointestinal tract
stasis and subsequent impaction. (Am J Vet Res
Objective—To characterize the effect of general
anesthesia and minor surgery on renal function in
Animals—9 mares with a mean (± SE) age and body
weight of 9 ± 2 years and 492 ± 17 kg, respectively.
Procedure—The day before anesthesia, urine was
collected (catheterization) for 3 hours to quantitate
baseline values, and serum biochemical analysis was
performed. The following day, xylazine (1.1 mg/kg, IV)
was administered, and general anesthesia was
induced 5 minutes later with diazepam (0.04 mg/kg,
IV) and ketamine (2.2 mg/kg, IV). During 2 hours of
anesthesia with isoflurane, PaCO2 was maintained
between 48 and 52 mm Hg, and mean arterial blood
pressure was between 70 and 80 mm Hg. Blood and
urine were collected at 30, 60, and 120 minutes during
and at 1 hour after anesthesia.
Results—Baseline urine flow was 0.92 ± 0.17 ml/kg/h
and significantly increased at 30 and 60 minutes after
xylazine administration (2.14 ± 0.59 and 2.86 ± 0.97
ml/kg/h respectively) but returned to baseline values
by the end of anesthesia. Serum glucose concentration
increased from 12 ± 4 to 167 ± 8 mg/dl at 30 minutes.
Glucosuria was not observed.
Conclusions and Clinical Relevance—Transient
hyperglycemia and an increase in rine production
accompanies a commonly used anesthetic technique
for horses. The increase in urine flow is not trivial and
should be considered in anesthetic management
decisions. With the exception of serum glucose concentration
and urine production, the effect of general
anesthesia on indices of renal function in clinically
normal horses is likely of little consequence in most
horses admitted for elective surgical procedures.
(Am J Vet Res 2002;63:1061–1065)
Objective—To evaluate the efficacy of intraluminal
administration of a customized solution during low-flow
ischemia and reperfusion in the jejunum of horses.
Sample Population—Segments of jejunum obtained
from 13 healthy adult horses.
Procedure—In isolated segments of jejunum maintained
in an extracorporeal circuit, arterial flow was
reduced to 20% of baseline for 40 minutes (ischemia)
followed by 60 minutes of reperfusion. In 2 groups, a
customized solution (concentrations, 12.5 and 25%,
respectively) was placed in the lumen prior to lowflow
ischemia and maintained during reperfusion. The
control group received intraluminal lactated Ringer's
solution for the same duration. Various metabolic,
hemodynamic, histologic, and permeability variables
Results—The 12.5% solution resulted in less histomorphologic
injury and reduced mucosal permeability
to albumin, compared with the 25% solution and the
lactated Ringer's solution. Morphologic injury and permeability
were reduced in tissues that received the
25% solution, compared with the control group, but
this difference was not significant.
Conclusions and Clinical Relevance—Use of a
12.5% customized solution appeared to minimize
injury in the isolated extracoporeal jejunal loop, which
provides some indication that it might be useful in
clinical situations. (Am J Vet Res 2002;63:1389–1394)
Objective—To evaluate the effect of 2 cyclooxygenase
(COX)-2 inhibitors on contractile activity of the
circular smooth muscle layer of the equine dorsal and
Sample Population—Samples of the dorsal and ventral
colon obtained from 10 healthy horses.
Procedure—Full-thickness tissue samples were collected
from the dorsal colon in the area of the
diaphragmatic flexure and the ventral colon in the
area of the sternal flexure. Samples were cut into
strips oriented along the fibers of the circular muscle
layer and mounted in a tissue bath system for determination
of contractile strength. Incremental
amounts of etodolac, nabumetone, and indomethacin
were added, and contractile activity was recorded.
Results—Response of the dorsal and ventral colon to
nonsteroidal anti-inflammatory drugs (NSAIDs) was
variable. Indomethacin induced the greatest reduction
in contractile activity, followed by nabumetone. For
etodolac, the difference from baseline values was
only significantly reduced at the highest concentration
used (1 × 10–5M) for the ventral colon.
Conclusions and Clinical Relevance—The NSAIDs that
are designed to target the COX-2 isoform appeared to
have variable effects on the contractile activity of the
equine dorsal and ventral colon. Etodolac appeared to
have the least effect on contractile activity, compared
with the effects attributable to nabumetone, and would
potentially have the fewest adverse effects relative to
motility of the dorsal and ventral colon. (Am J Vet Res
Objective—To develop an objective, accurate method
for quantifying forelimb ground reaction forces in
horses by adapting a human in-shoe pressure measurement
system and determine the reliability of the
system for shod and unshod horses.
Animals—6 adult Thoroughbreds.
Procedure—Horses were instrumented with a
human in-shoe pressure measurement system and
evaluated at a trot (3 m/s) on a motorized treadmill.
Maximum force, stance time, and peak contact area
were evaluated for shod and unshod horses. Three
trials were performed for shod and unshod horses,
and differences in the measured values were examined
with a mixed model ANOVA for repeated measures.
Sensor accuracy was evaluated by correlating
measured variables to clinically observed lameness
and by a variance component analysis.
Results—4 of 6 horses were determined to be lame
in a forelimb on the basis of clinical examination and
measured values from the system. No significant differences
were observed between shod and unshod
horses for maximum force and stance time. A significant
decrease in peak contact area was observed for
shod and unshod horses at each successive trial.
Maximum force measurements provided the highest
correlation for detecting lameness ( r = 0.91, shod
horses; r = 1.0, unshod horses). A variance component
analysis revealed that 3 trials provided a variance
of 35.35 kg for maximum force (± 5.78% accuracy),
0.007 seconds for stance time (± 2.5% accuracy), and
8.58 cm2 for peak contact area (± 11.95% accuracy).
Conclusions and Clinical Relevance—The in-shoe
pressure measurement system provides an accurate,
objective, and effective method to evaluate lameness
in horses. ( Am J Vet Res 2001;62:23–28)
Objective—To determine whether a customized solution
could attenuate the effects of low-flow ischemia
and reperfusion injury of the equine jejunum.
Sample Population—A segment of jejunum
obtained from 21 healthy adult horses.
Procedure—A segment of jejunum was maintained
in an isolated extracorporeal circuit, and
arterial flow was reduced to 20% of baseline for
40 minutes (ischemia) followed by 60 minutes of
reperfusion. In 1 group, a customized solution was
infused at a rate of 1 ml/min during low-flow
ischemia and 3 ml/min during reperfusion. In a
second group, the solution was infused at the
same rate during low-flow ischemia, but it was
infused at a rate of 7 ml/min during reperfusion.
Control groups received lactated Ringer's solution
administered at the same rates as for the customized
solution. Various metabolic, hemodynamic,
histologic, and permeability variables were
Results—A lower flow rate during reperfusion (3
ml/min) had a beneficial effect, compared with lactated
Ringer's solution or the higher flow rate (7
ml/min). Use of the solution at this rate resulted in
less histomorphologic injury and reduced mucosal
permeability to albumin.
Conclusions and Clinical Relevance—Use of a customized
solution at a lower flow rate during repurfusion
appeared to have a protective effect on equine
jejunum when administered IV during low-flow
ischemia and reperfusion. (Am J Vet Res 2001;
Objective—To determine the in vitro effect of
prostaglandin (PG) E2, PGF2α, and the nonsteroidal
anti-inflammatory drugs (NSAIDs) indomethacin,
ketoprofen, and nabumetone on the contractile
strength of the circular smooth muscle layer of the
third compartment of the stomach of llamas.
Sample Population—Specimens of the third compartment
obtained from 5 healthy adult llamas.
Procedure—Full-thickness tissue samples were collected
from the third compartment immediately after
euthanasia. Specimens were cut into strips oriented
along the circular muscle layer and mounted in a tissue
bath system. Incremental amounts of ketoprofen,
nabumetone, indomethacin, PGE2, and PGF2α were
added, and contractile strength (amplitude of contractions)
Results—Generally, PGE2 reduced contractile
strength of the circular smooth layer of the third compartment,
whereas PGF2α increased the strength of
contractions. The activity of the NSAIDs was generally
excitatory in a concentration-dependent manner,
although significant changes were induced only by
administration of indomethacin.
Conclusions and Clinical Relevance—On isolated
smooth muscle strips of the third compartment of llamas,
exogenous PGE2 and PGF2α had a variable effect
on contractile strength. Administration of the NSAIDs
did not inhibit contractility and would not be likely to
induce stasis of the third compartment in the
absence of an underlying disease process. (Am J Vet
Objective—To determine the role of nitric oxide and an
apamin-sensitive nonadrenergic noncholingeric inhibitory
transmitter on contractility of the ventral colon of horses.
Sample population—Strips of the circular and longitudinal
muscle layers and taenia of the ventral colon
from 14 horses.
Procedure—Muscle strips were suspended in tissue
baths and attached to force transducers. Contractile
activity of circular, longitudinal, and taenia muscle
strips in response to electrical field stimulation was
measured after addition of apamin and a nitric oxide
inhibitor, N-nitro-L-arginine methyl ester (L-NAME).
Results—Electrical field stimulation reduced contractile
activity in the circular muscle layer and taenia but
not the longitudinal muscle layer. Addition of L-NAME
significantly reduced inhibitory contractile activity at
all frequencies for the circular muscle layer, whereas
a significant effect was evident for the taenia only at
the highest frequency. The combination of L-NAME
and apamin resulted in a significant reduction in inhibition
of the taenia at all frequencies but for circular
muscle only at lower frequencies.
Conclusions and Clinical Relevance—Nitric oxide
and an apamin-sensitive neurotransmitter appear to
mediate a component of inhibitory transmission in the
circular muscle and taenia, but not the longitudinal
muscle layer, of the equine ventral colon. Nitric oxide
has a role in regulating contractile activity of the
equine ventral colon, and nitric oxide synthase
inhibitors may be useful in horses with ileus of the
large colon. (Am J Vet Res 2000;61:64–68)
Objective—To determine effects of cisapride and 5-hydroxytryptamine (5-HT) on the jejunum of horses.
Sample Population—Jejunal muscle strips from 8
Procedure—Muscle strips were suspended in isolated
muscle baths. Isometric stress responses to 5-HT
and cisapride, with and without specific antagonists,
Results—Muscle strips incubated with atropine and
tetrodotoxin responded to 5-HT and cisapride with an
increase in contractile force. The 5-HT caused a concentration-dependent increase in contractile amplitude,
with a maximum response (Emax) of 1,151 ± 214
g/cm2 and a molar concentration that induces contractile
force equal to 50% of maximum response
(EC50) of 0.028 ± 0.002 µM. Prior incubation with the
5-HT2 antagonist ketanserin decreased the Emax (626
± 147 g/cm2) and potency (EC50, 0.307 ± 0.105 µM) of
5-HT. Prior incubation with the 5-HT3 antagonist tropisetron
decreased the efficacy (Emax, 894 ± 184
g/cm2) to 5-HT. Cisapride also caused a concentrationdependent
increase in contractile amplitude, with an
Emax of 331 ± 82 g/cm2 and an EC50 of 0.302 ± 0.122
µM. Prior incubation with ketanserin decreased the
Emax (55 ± 17 g/cm2) and potency (EC50, 0.520 ± 0.274
µM) of cisapride.
Conclusion and Clinical Relevance—Stimulatory
effects of 5-HT and cisapride on circular smooth muscle
of equine jejunum are mediated primarily through
a noncholinergic effect. The effects of 5-HT are mediated,
at least partially, by 5-HT2 and 5-HT3 receptors,
whereas the effects of cisapride are mediated primarily
by 5-HT2 receptors. This may impact treatment of
horses with postoperative ileus. (Am J Vet Res