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Abstract

Objective—To identify indications for and short- and long-term outcome of permanent tracheostomy performed in standing horses.

Design—Retrospective case series.

Animals—82 horses undergoing permanent tracheostomy.

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.

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in Journal of the American Veterinary Medical Association
in Journal of the American Veterinary Medical Association

Abstract

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 tract disease.

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)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine short- and long-term outcomes, including recurrence rates, for horses with cecal impaction treated medically or surgically.

Design—Retrospective case series.

Animals—114 horses.

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.

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in Journal of the American Veterinary Medical Association

Abstract

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)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To identify risk factors for enterolithiasis in horses.

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 enterolithiasis.

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 2000;216:1787–1794)

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in Journal of the American Veterinary Medical Association

Abstract

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 7 horses.

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 10–4 M (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 at 10–4 M 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)

Full access
in American Journal of Veterinary Research

Abstract

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)

Full access
in American Journal of Veterinary Research

Abstract

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 administered acetaminophen.

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 2000;61:310–315)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine risk factors associated with development of postoperative ileus in horses undergoing surgery for colic.

Design—Case-control study

Animals—69 horses that developed ileus after surgery for colic and 307 horses that did not develop postoperative ileus.

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 Assoc 2001;219:72–78)

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in Journal of the American Veterinary Medical Association