Procedures—Data obtained from medical records included signalment, diagnosis, surgical technique, complications, use of the horse before and after surgery, and owner satisfaction. Follow-up information was obtained through a telephone questionnaire administered to owners.
Results—Indications for permanent tracheostomy included nasopharyngeal cicatrix (n = 59), arytenoid chondropathy (55), and laryngeal hemiplegia (20); 54 horses had multiple indications for tracheostomy. Complications identified prior to discharge included partial dehiscence (n = 8), transient fever (10), and excessive swelling (13). Complications identified after discharge included partial dehiscence (n = 3), inversion of skin (2), and stenosis of the tracheostomy requiring repair (1). Long-term follow-up information was available for 64 horses. Fifty-seven of the 64 (89%) horses returned to their previous use, and owners of 63 (98%) horses reported being very satisfied with the results. The owner of 1 (2%) horse was unsatisfied with the results. The 1-year survival rate was 97% (95% confidence interval, 95% to 100%). Mean estimated truncated survival time (ie, failure-free period) was 9.7 years (95% confidence interval, 9.3 to 10.1 years).
Conclusions and Clinical Relevance—Results suggested that permanent tracheostomy can be safely performed in standing horses and was a viable treatment for horses with obstructive disease of the upper respiratory tract that was unresponsive to medical treatment or other surgical treatments.
Objective—To evaluate electrical activity of jejunal circular
muscle in horses and characterize electrical
responses to stimulation by intrinsic inhibitory neurons.
Sample Population—Portions of jejunum obtained
from horses euthanatized for reasons other than gastrointestinal
Procedure—Isolated circular muscle preparations
were perfused with oxygenated modified Krebs solution.
Glass microelectrodes were used for intracellular
recording of membrane potentials from single
smooth muscle cells. Electrical activity and responses
to electrical field stimulation (EFS) of intrinsic neurons
in the presence of guanethidine and atropine were
recorded. Mediators of responses to nerve stimulation
were also evaluated, using N-nitro-L-arginine
methyl ester (L-NAME) and apamin.
Results—Mean resting membrane potential (RMP)
was 41.5 ± 1.8 mV. Small membrane potential oscillations
were observed in muscle cells. Single or multiple
action potentials were often superimposed on
the peaks of these oscillations. Spontaneous oscillations
and action potentials were blocked by nifedipine.
Transient hyperpolarizations of smooth muscle
cell membrane potentials (inhibitory junction potentials
[IJP]) were observed in response to electrical
field stimulation. The IJP evoked by stimulus trains
consisted of an initial fast component followed by a
slow component. The L-NAME did not have a significant
effect on RMP and did not significantly affect the
fast component of IJP at any stimulus frequency tested.
In contrast, L-NAME abolished the slow component
of IJP observed after trains of pulses. In the continued
presence of L-NAME, apamin had no significant
effect on RMP but effectively reduced the fast
component of IJP.
Conclusions and Clinical Relevance—Findings suggest
that inhibitory neurotransmitters supplying
equine jejunum act through different ionic mechanisms.
Understanding these mechanisms may suggest
new therapeutic targets for treatment of motility
disorders. (Am J Vet Res 2000;61:362–368)
Objective—To determine short- and long-term outcomes, including recurrence rates, for horses with cecal impaction treated medically or surgically.
Design—Retrospective case series.
Procedures—Medical records were reviewed for information on signalment, history, clinical findings, treatment (medical vs surgical), and short-term outcome. Information on longterm outcome was obtained through a mail survey and telephone interview with owners.
Results—54 horses were treated medically, 49 horses were treated surgically, and 11 horses were euthanized after initial examination without further treatment. Horses treated surgically were significantly more likely to have signs of moderate or severe pain than were horses treated medically. Forty-four of the 54 (81%) horses treated medically were discharged from the hospital. Twelve of the 49 horses treated surgically were euthanized at surgery because of cecal rupture. Thirty-five of the 37 (95%) horses that were allowed to recover from surgery were discharged from the hospital. In 34 horses treated surgically, typhlotomy without a bypass procedure was performed. Long-term (≥ 1 year) follow-up information was available for 19 horses treated medically and 28 horses treated surgically. Eighteen (95%) and 25 (89%) of the horses, respectively, were alive at least 1 year after treatment.
Conclusions and Clinical Relevance—Results suggested that medical and surgical treatment were both associated with favorable outcomes in horses with cecal impactions. In this population, typhlotomy alone without cecal bypass was associated with a low recurrence rate. The long-term prognosis for horses that were discharged from the hospital was good.
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 identify risk factors for enterolithiasis
Design—Matched case-control study.
Animals—26 horses with enteroliths, 104 horses
with other causes of colic that underwent surgery (52
horses, surgical control group) or were treated medically
(52 horses, nonsurgical control group).
Procedure—Medical records were reviewed for horses
with enteroliths and control horses. Information
collected included signalment, anamnesis, and findings
on physical examination and clinicopathologic
testing at admission. Horses with enteroliths and control
horses were compared by means of conditional
logistic regression to identify factors associated with
Results—Horses that were fed alfalfa hay, spent ≤
50% of time outdoors, or were Arabian or miniature
breeds had an increased risk of developing
enteroliths. Horses with enteroliths were more likely
to have been hyperbilirubinemic and to have had clinical
signs > 12 hours prior to admission.
Conclusions and Clinical Relevance—Breed and
diet appear to influence the risk of enterolithiasis;
other management factors also may influence development
of enteroliths. Duration of clinical signs may
be longer and signs may be less severe among horses
with enteroliths, compared with horses with
other causes of colic. (J Am Vet Med Assoc
Objective—To evaluate effects of erythromycin, lidocaine,
and metoclopramide on smooth muscle of the
pyloric antrum (PA), proximal portion of the duodenum
(PD), and middle portion of the jejunum (MJ) of horses.
Sample Population—Strips of smooth muscle from
Procedure—Isolated muscle strips were suspended in a
bath and attached to isometric force transducers. Once
stable spontaneous contractions were observed, agents
were added. Isometric stress responses were compared
with the amplitude of spontaneous contractions.
Results—A single dose of erythromycin to the PA
increased contractile amplitude (CA) for the longitudinal
smooth muscle (mean ± SEM, 76 ± 16 g/cm2) but
decreased CA for circular smooth muscle
(–79 ± 23 g/cm2). The inhibitory effect was decreased
by tetrodotoxin, NG-nitro-L-arginine methyl ester, and a
vasoactive intestinal peptide antagonist. Erythromycin
increased CA for the MJ, which was maximal at 10–4M
(171 ± 36 g/cm2). Lidocaine increased CA for the PD,
which was maximal at 10–4M (60 ± 5 g/cm2).
Metoclopramide increased the CA, which was maximal
for the PA (75 ± 26 g/cm2), PD
(279 ± 33 g/cm2), and MJ (456 ± 59 g/cm2).
Conclusions—Regional differences in responses to
erythromycin, lidocaine, and metoclopramide were
evident in the gastrointestinal tract of horses.
Metoclopramide increased CA in all tissues used,
whereas erythromycin inhibited CA in circular smooth
muscle but stimulated CA in longitudinal smooth
muscle from the PA. Inhibition is caused by stimulation
of inhibitory nerves and is mediated, in part, by
nitric oxide and vasoactive intestinal peptide. (Am J Vet Res 2000;61:413–419)
Objective—To determine whether ether-a-go-go
(ERG) potassium channels are expressed in equine
gastrointestinal smooth muscle, whether ERG channel
antagonists affect jejunal muscle contraction in
vitro, and whether plasma cisapride concentrations in
horses administered treatment for postoperative ileus
(POI) are consistent with ERG channels as drug targets.
Sample Population—Samples of intestinal smooth
muscle obtained from 8 horses free of gastrointestinal
tract disease and plasma samples obtained from
3 horses administered cisapride for treatment of POI.
Procedure—Membranes were prepared from the
seromuscular layer of the duodenum, jejunum, ileum,
cecum, large colon, and small colon. Immunoblotting
was used to identify the ERG channel protein.
Isolated jejunal muscle strips were used for isometric
stress response to ERG channel blockers that included
E-4031, MK-499, clofilium, and cisapride. Plasma
concentrations of cisapride were determined in 3
horses administered cisapride for treatment of POI
after small intestinal surgery.
Results—Immunoblotting identified ERG protein in all
analyzed segments of the intestinal tract in all horses.
The selective ERG antagonist E-4031 caused a concentration-
dependent increase in jejunal contraction.
Clofilium, MK-499, and cisapride also increased jejunal
contraction at concentrations consistent with ERG
channel block; effects of E-4031 and cisapride were
not additive. Peak plasma cisapride concentrations in
treated horses were consistent with ERG block as a
mechanism of drug action.
Conclusions and Clinical Relevance—The ERG
potassium channels modulate motility of intestinal
muscles in horses and may be a target for drugs. This
finding may influence development of new prokinetic
agents and impact treatment of horses with POI.
(Am J Vet Res 2003;64:267–272)
Objective—To evaluate the correlation between halftime
of liquid-phase gastric emptying (T50), determined
with nuclear scintigraphy using technetium
Tc 99m pentetate, and absorption variables of orally
Animals—6 mature horses.
Procedure—Technetium Tc 99m pentetate (10 mCi)
and acetaminophen (20 mg/kg of body weight) were
administered simultaneously in 200 ml of water. Serial
left and right lateral images of the stomach region
were obtained with a gamma camera, and T50 determined
separately for counts obtained from the left
side, the right side and the geometric mean. Power
exponential curves were used for estimation of T50
and modified R2 values for estimation of goodness of
fit of the data. Serial serum samples were taken, and
acetaminophen concentration was determined, using
fluorescence polarization immunoassay. Maximum
serum concentration (Cmax), time to reach maximum
serum concentration (Tmax), area under the curve for
240 minutes and the absorption constant (Ka) were
determined, using a parameter estimation program.
Correlations were calculated, using the Spearman
rank correlation coefficient.
Results—Correlations between T50 and Tmax and
between T50 and Ka were significant.
Conclusions and Clinical Relevance—Tmax and Ka
are valuable variables in the assessment of liquidphase
gastric emptying using acetaminophen absorption.
Acetaminophen absorption may be a valuable
alternative to nuclear scintigraphy in the determination
of gastric emptying rates in equine patients with
normally functioning small intestine. (Am J Vet Res
Objective—To determine risk factors associated with
development of postoperative ileus in horses undergoing
surgery for colic.
Animals—69 horses that developed ileus after
surgery for colic and 307 horses that did not develop
Procedure—Signalment, history, clinicopathologic
data, treatment, lesions, and outcome were obtained
from medical records.
Results—Variables associated with increased risk of
postoperative ileus included age > 10 years, Arabian
breed, PCV ≥ 45%, high serum concentrations of protein
and albumin, anesthesia > 2.5 hours' duration,
surgery > 2 hours' duration, resection and anastomosis,
and lesions in the small intestine. Enterotomy
reduced the risk of postoperative ileus. After multivariate
logistic regression, the final model included
the variables Arabian breed, PCV ≥ 45%, lesion type,
duration of surgery (> 2 hours vs ≤ 2 hours), and
pelvic flexure enterotomy.
Conclusions and Clinical Relevance—Results suggest
that by evaluating certain factors, horses at
increased risk of postoperative ileus may be recognized
before the condition develops. Preventative
treatment and early intervention may be instituted in
these horses. Shortening surgery time and performing
an enterotomy may decrease the probability of
horses developing postoperative ileus. (J Am Vet Med