Effects of intravenous ethyl pyruvate on cardiopulmonary variables and quality of recovery from anesthesia in horses.

OBJECTIVE: To determine the effects of intravenous ethyl pyruvate, an anti-inflammatory with putative benefits in horses with endotoxemia, on cardiopulmonary variables during anesthesia and the quality of anesthetic recovery. STUDY DESIGN: Randomized, crossover, blinded experimental design. ANIMALS: A total of six healthy Standardbred geldings, aged 13 ± 3 years and weighing 507 ± 66 kg (mean ± standard deviation). METHODS: Horses were anesthetized for approximately 90 minutes on two occasions with a minimum of 2 weeks apart using xylazine for sedation, ketamine and diazepam for induction, and isoflurane in oxygen for maintenance. Lactated Ringer's solution (LRS; 10 mL kg-1 hour-1) was administered during anesthesia. Treatments were randomized and administered starting approximately 30 minutes after induction of anesthesia and infused over 60 minutes: LRS (1 L) or ethyl pyruvate (150 mg kg-1 in 1 L LRS). Invasive arterial pressures, heart rate, respiratory rate and end-tidal carbon dioxide tensions were recorded every 5 minutes for the duration of anesthesia. Arterial blood gases, glucose and lactate concentrations were measured every 20 minutes. Anesthetic recovery was video recorded, stored, and subsequently rated by two individuals blinded to treatments. Total recovery time, time to extubation, number of attempts and time to sternal recumbency, number of attempts to stand and time to stand were recorded. Quality of recovery was analyzed. Data between treatments and within a treatment were assessed using two-way repeated-measures anova and a Pearson correlation coefficient, significant at p < 0.05. RESULTS: All horses completed the study. No significant differences were detected between the ethyl pyruvate and LRS treatments for either the cardiopulmonary variables or quality of recovery from anesthesia. CONCLUSIONS AND CLINICAL RELEVANCE: The results suggest that intravenous ethyl pyruvate can be administered to healthy anesthetized horses with minimal impact on the cardiopulmonary variables studied or the quality of recovery from anesthesia.

Multicenter Placebo-Controlled Randomized Study of Ethyl Pyruvate in Horses Following Surgical Treatment for ≥ 360° Large Colon Volvulus.

Identifying therapies that mitigate ischemic colonic injury and improve mucosal healing and intestinal viability are crucial to improving survival in horses with ≥360° large colon volvulus (LCV). Ethyl pyruvate is the ethyl ester of pyruvate with diverse pharmacologic effects that limit ischemic injury and hasten intestinal mucosal repair in preclinical rodents, sheep and swine models. The objective of this study was to determine the effects of ethyl pyruvate on systemic indices of colon viability, expression of inflammatory genes in whole blood, morbidity and survival after surgical correction of LCV compared to controls. Horses received either 150 mg/kg ethyl pyruvate in 1 liter lactated Ringer's solution (LRS) or 1 liter LRS intravenously (IV) every 6 h for 24 h following surgical recovery for correction of LCV. Colic duration, perioperative heart rate (HR), packed cell volume (PCV), total solids (TS), blood L-lactate concentration, surgical time, intraoperative episodes of hypoxemia and hypotension, expression of inflammatory cytokine genes, fecal consistency and survival to hospital discharge were compared between ethyl pyruvate treated horses and controls. Twenty-two horses, 12 receiving ethyl pyruvate and 10 controls, were enrolled in the study. Ethyl pyruvate was safely administered to horses following surgical correction of LCV. No significant effects of ethyl pyruvate on post-operative variables, including survival, were found. Seven of 12 ethyl pyruvate treated horses and 5/10 controls survived to hospital discharge. Higher HR, PCV and blood L-lactate concentration at the time of hospital admission, P = 0.005, 0.01, 0.04, respectively, 24 h after surgery, P = 0.001, 0.03, 0.02, respectively, were associated with death. Heart rate, P = 0.005, 48 h after surgery was associated with death. Ethyl pyruvate was safely administered to horses following correction of LCV with no apparent adverse events but was not associated with improved post-operative outcomes including survival. A larger, randomized control trial is needed to fully evaluate the effectiveness of ethyl pyruvate. A major limitation of this investigation is the small sample size, making the study underpowered and creating a high possibility of type II error.

Incisional infections associated with ventral midline celiotomy in horses.

OBJECTIVE: To review the veterinary literature regarding healing and complications associated with equine celiotomy including anatomy and physiology, risk factors for incisional infection and hernia, and treatment. ETIOLOGY: Celiotomy is the most common approach to treat horses with surgical colic. Incision through the linea alba provides exposure to most of the abdomen for exploration, exteriorization, and correction of surgical lesions. Incisional apposition relies on suture strength during anesthetic recovery and for the first 30 days postoperatively. Factors associated with the patient, surgical lesion and procedures, anesthesia, and recovery put the horse at risk for surgical site infection. Infection is the most important risk factor for incisional hernia formation. DIAGNOSIS: A presumptive diagnosis of surgical site infection is made based on the presence of fever and incisional swelling, pain, and discharge. Ultrasonography can be used to identify areas of fluid accumulation prior to the appearance of incisional drainage. Definitive diagnosis is based on positive bacteriologic culture of the incisional discharge. Incisional hernia is diagnosed by palpation of the incision, usually 30-60 days after surgery. Ultrasound of the incision may aide in early diagnosis of incisional hernia if gaps along the incision in the linea alba are apparent. THERAPY: No objective data exist to assess the efficacy of specific therapies for surgical site infections following celiotomy. Principles of treatment include the establishment of drainage, bandaging, antimicrobial therapy based on culture and sensitivity, and extended rest in an attempt to avoid incisional hernia or dehiscence. Treatment for incisional hernia includes prolonged circumferential bandaging, open or minimally invasive hernia repair, or no treatment. PROGNOSIS: Incisional complications are associated with prolonged convalescence and diminished prognosis for return to athleticism. Limiting risk factors for surgical site infections, prompt treatment, and incisional support may optimize celiotomy healing and timely return to function. Horses compete in many disciplines with incisional hernias.

Preliminary heritability of complete rotation large colon volvulus in Thoroughbred broodmares.

Large colon volvulus (LCV) is a life-threatening form of colic that occurs when the large colon rotates 360° or more on its axis, resulting in colonic distention and ischaemia. Any horse can suffer from LCV, but the risk is greatest for periparturient Thoroughbred broodmares; the objective of this study was to estimate the heritability of LCV in these horses. The criteria for classification as an LCV case were being a Thoroughbred broodmare from one of three farms in central Kentucky and having had surgical correction for LCV. Controls were identified as Thoroughbred broodmares present on the same farms with no history of surgical colic. Thirty-nine cases and 191 controls were identified. Age of the LCV cases at the time of incident was significantly younger than that of the controls at the time of the study (P<0.0001). A total of 2223 horses were present when the five-generation pedigrees of the 230 study horses were combined. Heritability of LCV was estimated at 0.311±0.383 from the fit of a logit sire model with binomial data including year of birth and farm as fixed effects. Further data on broodmares from these and other farms will help to improve this estimate, which suggests the LCV is moderately heritable.

The Effect of Core Abdominal Muscle Rehabilitation Exercises on Return to Training and Performance in Horses After Colic Surgery.

We conducted a retrospective cohort study to test the hypothesis that performing 4 weeks of core abdominal rehabilitation exercises (CARE) postoperatively would be safe and associated with faster return to training and improved performance after colic surgery. Performance horses that recovered from colic surgery performed by the same surgeon and survived ≥ 1 year from 2008 to 2017 were included. Data were obtained from a review of medical records. Information about the horses' rehabilitation and performance was obtained from owners/trainers. Data from horses that completed a 4-week CARE program after surgery were compared with control horses that did not do the exercises after colic surgery. Data were analyzed using univariate and multiple regression, P < .05. Eleven CARE horses and 51 controls between the ages of 3 and 18 years were included in the data analysis. All CARE horses completed the rehabilitation program with no reported complications, returned to work faster after surgery, P = .002, and to training faster, P = .0002. After colic surgery, 81% of CARE horses improved their performance level compared with 7.8% of controls, P < .001. Core abdominal rehabilitation exercises were safely performed by horses after colic surgery with no reported complications and may have facilitated faster convalescence and improved performance.

Effects of hyaluronate-carboxymethylcellulose membranes on the clinical outcome of horses undergoing emergency exploratory celiotomy.

OBJECTIVE: To determine the influence of hyaluronate-carboxymethylcellulose (HA-CMC) membranes applied to intestinal anastomoses or enterotomies on postoperative complications after emergency exploratory celiotomy. STUDY DESIGN: Multicenter retrospective case-controlled series. ANIMALS: Adult horses (59 in the HA-CMC group and 91 controls). METHODS: Medical records from 4 referral hospitals were searched for horses ≥1 year of age, treated between 2008 and 2014 with emergency exploratory celiotomy, and surviving at least 24 hours postoperatively. Horses receiving repeat celiotomy during the same hospitalization were excluded. Horses who received HA-CMC were matched with controls who did not receive HA-CMC but had similar intestinal lesions and procedures at the same referral hospital. Postoperative complications (colic, nasogastric reflux, fever, incisional infection, and septic peritonitis), duration of hospitalization, and survival were compared between groups. Data were compared between horses by t test, Wilcoxon signed rank test, and χ2 test. RESULTS: The volume of nasogastric reflux at admission (P = .02) and the duration of administration of lidocaine after surgery (P = .02) were greater in horses with HA-CMC membranes than in controls. No difference in postoperative complications or survival was detected between groups: 48 of 59 (81%) horses treated with HA-CMC survived until discharge from the hospital compared with 80 of 91 (88%) horses in the control group (P = .27). Fifteen of 21 horses treated with HA-CMC and 30 of 43 horses in the control group survived >12 months after hospital discharge. CONCLUSION: Application of HA-CMC membranes to anastomoses or intestinal incisions did not influence postoperative complications or survival after emergency celiotomy compared with controls. CLINICAL SIGNIFICANCE: The safety and efficacy of HA-CMC membrane application to intestinal sites during colic surgery in horses is equivocal.

Oxidative stress-induced mitochondrial dysfunction in a normal colon epithelial cell line.

AIM: To determine how a normal human colon cell line reacts to microbial challenge as a way to study oxidative stress-induced responses associated with inflammatory bowel disease. METHODS: Normal human colon epithelial cells (ATCC® CRL.1790™) were stimulated with either heat killed E. coli or heat killed murine cecal contents (HKC) and examined for several relevant biomarkers associated with inflammation and oxidative stress including cytokine production, mitochondrial autophagy and oxidant status. TNFα, IL-1ß and IL-8 protein concentrations were measured within the supernatants. Fluorescent microscopy was performed to quantify the production of reactive oxygen species (ROS) using an oxidation responsive fluorogenic probe. Mitochondrial morphology and mitochondrial membrane potential was assessed by dual staining using COXIV antibody and a dye concentrating in active mitochondria. Mitochondrial ROS scavenger was used to determine the source of ROS in stimulated cells. Autophagy was detected by staining for the presence of autophagic vesicles. Positive controls for autophagy and ROS/RNS experiments were treated with rapamycin and chloroquine. Mitochondrial morphology, ROS production and autophagy microscopy experiments were analyzed using a custom acquisition and analysis microscopy software (ImageJ). RESULTS: Exposing CRL.1790 cells to microbial challenge stimulated cells to produce several relevant biomarkers associated with inflammation and oxidative stress. Heat killed cecal contents treatment induced a 10-12 fold increase in IL-8 production by CRL.1790 cells compared to unstimulated controls at 6 and 12 h (P < 0.001). Heat killed E. coli stimulation resulted in a 4-5 fold increase in IL-8 compared to the unstimulated control cells at each time point (P < 0.001). Both heat killed E. coli and HKC stimulated robust ROS production at 6 (P < 0.001), and 12 h (P < 0.01). Mitochondrial morphologic abnormalities were detected at 6 and 12 h based on reduced mitochondrial circularity and decreased mitochondrial membrane potential, P < 0.01. Microbial stimulation also induced significant autophagy at 6 and 12 h, P < 0.01. Lastly, blocking mitochondrial ROS generation using mitochondrial specific ROS scavenger reversed microbial challenge induced mitochondrial morphologic abnormalities and autophagy. CONCLUSION: The findings from this study suggest that CRL.1790 cells may be a useful alternative to other colon cancer cell lines in studying the mechanisms of oxidative stress events associated with intestinal inflammatory disorders.

Duration of in vivo endotoxin tolerance in horses.

Endotoxemia models are used to study mechanisms and treatments of early sepsis. Repeated endotoxin exposures induce periods of endotoxin tolerance, characterized by diminished proinflammatory responses to lipopolysaccharide (LPS) and modulated production of proinflammatory cytokines. Repeated measure designs using equine endotoxemia models are rarely performed, despite the advantages associated with reduced variability, because the altered responsiveness would confound study results and because the duration of equine endotoxin tolerance is unknown. We determined the interval of endotoxin tolerance, in vivo, in horses based on physical, clinicopathologic, and proinflammatory gene expression responses to repeated endotoxin exposures. Six horses received 30 ng/kg LPS in saline infused over 30 min. Behavior pain scores, physical examination parameters, and blood for complete blood count and proinflammatory gene expression were obtained at predetermined intervals for 24h. Horses received a total of 3 endotoxin exposures. The first exposure was LPS 1, followed 7 days later by LPS 7 or 14-21 days later by LPS 14-21. Lipopolysaccharide exposures were allocated in a randomized, crossover design. Lipopolysaccharide produced clinical and clinicopathologic signs of endotoxemia and increased expression of tumor necrosis factor alpha (TNFα), interleukin (IL)-6 and IL-8, P<0.001. Horses exhibited evidence of endotoxin tolerance following LPS 7 but not following LPS 14-21. Horses had significantly lower pain scores, heart rates, respiratory rates and duration of fever, after LPS 7 compared to LPS 1 and LPS 14-21, P<0.001, and expression of TNFα was lower in the whole blood of horses after LPS 7, P=0.05. Clinical parameters and TNFα gene expression were similar or slightly increased in horses following LPS 14-21 compared to measurements made in horses following LPS 1, suggesting that endotoxin tolerance had subsided. A minimum of 3 weeks between experiments is warranted if repeated measures designs are used to assess in vivo response to endotoxin in horses.

End-to-Side Versus Side-to-Side Jejunocecostomy in Horses: A Retrospective Analysis of 150 Cases.

OBJECTIVES: To determine factors associated with postoperative reflux, postoperative colic, repeat celiotomy, and survival in horses after end-to-side (E2S) or side-to-side (S2S) jejunocecostomy. STUDY DESIGN: Retrospective, multicenter study. SAMPLE POPULATION: Horses (n = 150). METHODS: Admissions, intra- and postoperative data were collected from medical records of horses that had E2S or S2S jejunocecostomy. Descriptive statistics were calculated and data were analyzed using parametric and nonparametric tests, linear and multivariate logistic regression with significance set at P < .05. Kaplan-Meier estimate of the survival function was performed. RESULTS: One hundred fifty horses (S2S = 90, E2S = 60) were included. S2S procedures were performed using staples (n = 57) or hand-sewn (33). Method of anastomosis was not significantly associated with development of postoperative reflux or colic, repeat celiotomy, whether the horse was alive at hospital discharge or 12 months after discharge. The number of years that the principal surgeon was boarded by the American College of Veterinary Surgeons significantly affected whether the horse was discharged from the hospital alive (P = .003). Age (P = .006) was significantly associated with 12-month survival. Increased age (P = .013) and administration of prokinetic medication (P = .0006) were significantly associated with development of postoperative reflux. Sixty-eight (76%) horses with S2S and 52 (87%) horses with E2S were discharged alive. CONCLUSION: Age, patient related variables, and surgeon experience may influence morbidity and mortality more than method of jejunocecostomy.

Ethyl pyruvate decreases proinflammatory gene expression in lipopolysaccharide-stimulated equine monocytes.

Monocytes are among the initial cells that interact with circulating LPS. Binding of LPS to monocyte surface receptors triggers an intracellular signaling cascade and results in the production of proinflammatory cytokines. Ethyl pyruvate, a stable derivative of pyruvate, has been effective in mitigating LPS induced alterations in isolated human monocytes. We hypothesized that ethyl pyruvate would suppress proinflammatory gene expression in LPS-stimulated equine monocytes without affecting cell viability. Equine monocytes were isolated from whole blood using a sediment-gradient centrifugation protocol and enriched to 76% purity by adhesion to tissue culture dishes. Isolated monocytes were incubated with 0, 1, 5, 10 and 50 mM ethyl pyruvate. Cell viability, production of caspase 3/7, and caspase-3 gene expression were determined. In a separate experiment, monocytes were stimulated with LPS (0.1 ng/ml for 1h) followed by incubation with 0, 1, 5, or 10 mM ethyl pyruvate for 1 h. Proinflammatory gene expression was determined by real-time PCR. Ethyl pyruvate at 50 mM adversely affected monocyte viability. Ethyl pyruvate at 10mM or less had no significant effect on monocyte viability, and did not increase activity of caspase 3/7 nor caspase-3 gene expression. Incubation with LPS alone induced a significant upregulation in proinflammatory gene expression. Subsequent treatment of monocytes with ethyl pyruvate significantly reduced IL-8 expression in LPS stimulated monocytes at 5 mM, and IL-8, TNF-α and COX-2 at 10 mM. No beneficial effect on expression of IL-1ß or IL-6 was detected. Overall, 10 mM ethyl pyruvate did not adversely affect monocyte viability and suppressed LPS-induced proinflammatory gene expression. Ethyl pyruvate may be a beneficial anti-inflammatory therapy in equine endotoxemia.

Resection and anastomosis of the descending colon in 43 horses.

OBJECTIVES: To determine (1) the short- (to hospital discharge) and long- (>6 months) term survival, (2) factors associated with short-term survival, and (3) the perioperative course for horses with resection and anastomosis of the descending colon. STUDY DESIGN: Multicentered case series. ANIMALS: Horses (n=43) that had descending colon resection and anastomosis. METHODS: Medical records (January 1995-June 2009) of 7 equine referral hospitals were reviewed for horses that had descending colon resection and anastomosis and were recovered from anesthesia. Retrieved data included history, results of clinical and clinicopathologic examinations, surgical findings, postsurgical treatment and complications, and short-term survival (hospital discharge). Long-term survival was defined as survival > or =6 months after hospital discharge. RESULTS: Of 43 horses, 36 (84%) were discharged from the hospital. Twenty-eight of 30 horses with follow-up information survived > or =6 months. No significant associations between perioperative factors and short-term survival were identified. Lesions included strangulating lipoma (n=27), postfoaling trauma (4), infarction (4), intraluminal obstruction (2), and other (6). Common postoperative complications included fever and diarrhea. During hospitalization 7 horses were euthanatized or died because of septic peritonitis (3), endotoxemia (3), and colic and ileus (1). CONCLUSIONS: Descending colon resection and anastomosis has a favorable prognosis for hospital discharge and survival > or =6 months. The most common cause of small colon incarceration was strangulating lipoma. CLINICAL RELEVANCE: Complications include postoperative fever and diarrhea but the prognosis is good after small colon resection and anastomosis.

Spurious hypercreatininemia: 28 neonatal foals (2000-2008).

OBJECTIVES: To (1) determine the occurrence of spurious hypercreatininemia in a population of hospitalized foals<2 days old, (2) assess the resolution of the hypercreatininemia, and (3) determine its association with survival in these foals. DESIGN: Retrospective case series. SETTING: 2 Referral hospitals. ANIMALS: Foals<2 days old with an admission creatinine>442 micromol/L (>5.0 mg/dL) from 2 referral hospitals. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The medical records of 33 foals were reviewed. Twenty-eight had spurious hypercreatininemia and 5 had acute renal failure. Admission creatinine was not significantly different between the 2 groups (mean [standard deviation]). The creatinine was 1,202 micromol/L (663 micromol/L) (13.6 mg/dL [7.5 mg/dL]) versus 1,185 micromol/L (787 micromol/L) (13.4 mg/dL [8.9 mg/d]) (P=0.96) in each group, respectively, though BUN at the time of hospital admission was significantly higher for acute renal failure foals (P=0.009). In the spurious group, serum creatinine at admission decreased to 504 micromol/L (380 micromol/L) (5.7 mg/dL [4.3 mg/dL]) by 24 hours, and to 159 micromol/L (80 micromol/L) (1.8 mg/dL [0.9 mg/dL]) at 48 hours, and to 115 micromol/L (44 micromol/L) (1.3 mg/dL [0.5 mg/dL]) at 72 hours. Twenty-three of 28 foals with spurious hypercreatininemia survived to hospital discharge and there was no difference in mean admission creatinine between survivors (1176 micromol/L [628 micromol/L]) (13.3 mg/dL [7.1 mg/dL]) and nonsurvivors (1308 micromol/L [857 micromol/L]) (14.8 mg/dL [9.7 mg/dL]) (P=0.67). Twenty of 28 foals had clinical signs suggestive of neonatal encephalopathy. CONCLUSION: Creatinine decreased by >50% within the initial 24 hours of standard neonatal therapy and was within the reference interval in all but 1 foal within 72 hours of hospitalization. The diagnosis of neonatal encephalopathy was common in these foals.

Prevalence of and risk factors for postoperative ileus after small intestinal surgery in two hundred and thirty-three horses.

OBJECTIVES: To determine the incidence of postoperative ileus (POI) in a population of horses after small intestinal surgery and the effect of multiple variables on development of POI. STUDY DESIGN: Case series. ANIMALS: Horses (n=233) aged > or =1 year that had exploratory celiotomy for small intestinal disease that recovered from surgery from 1995 to 2005. METHODS: Sixty-eight variables were collected from medical records (1995-2005) for each horse. POI was defined as nasogastric reflux volume >20 L over 24 hours or >8 L at any single time after surgery. RESULTS: Twenty-seven percent (64/233) of horses developed POI; 29 of 64 (46%) horses with POI had duodenitis proximal jejunitis (DPJ). When no intestinal resection was required at surgery, excluding horses with DPJ, 15% of horses had POI; 30% horses had POI after intestinal resection. Ten percent of horses had POI for >24 hours. When horses with DPJ were excluded, factors associated with increased risk of POI included high packed cell volume at hospital admission (P=.024), increasing age (P=.0004), and length of intestinal resection (P=.05). CONCLUSIONS: Risk factors for POI in this study were nonspecific although horses with intestinal resection are at higher risk compared with horses without intestinal resection. CLINICAL RELEVANCE: Predicting with certainty which cases will develop POI remains elusive.

Nutrition of critically ill horses.

Nutritional supplementation is becoming the standard of practice in equine medicine, although there are minimal data on nutritional support in critically ill horses and its association or effect on morbidity and mortality or length of hospital stay. Horses can be fed orally and when that is not possible, intravenously or parenterally. Enteral feeding is less expensive, more physiologic, improves immunity, and is easier and safer. This article reviews available information on the development of a nutritional plan for critically ill horses, and describes methods for and complications of enteral and parenteral feeding.

Objective radiographic assessment of abdominal sand accumulation in horses.

Gastrointestinal sand accumulation is a common cause of equine colic. Subjective assessment of sand accumulation on abdominal radiographs has been used as a diagnostic aid; however, there is poor correlation between clinical, diagnostic, and surgical findings. The purpose of this study was to develop an objective method of assessing radiographic sand accumulation in order to improve the diagnostic utility of radiography for sand colic. Fifty-one equine abdominal radiographic examinations were reviewed, with approximately half of the imaged patients having a clinical diagnosis of sand colic. Initially, four observers independently reviewed these radiographic studies to subjectively decide whether or not sand accumulation was sufficient to cause colic. Subsequently, an objective scoring system was developed using various radiographic parameters that yielded a score ranging from one to 12 for quantity and apparent density of sand accumulation. Inter- and intraobserver results using the subjective scoring method had significant differences among all observers. Subjective assessment was also deemed to be inaccurate for colic prediction. Using the objective scoring system, there were no significant differences between or within the observers' results. A score of seven out of 12 was found to have an 83% likelihood of being associated with a positive diagnosis of sand colic. The designed objective scoring method creates a more uniform and accurate method to assess the sand accumulation.

Plasma lactate as a predictor of colonic viability and survival after 360 degrees volvulus of the ascending colon in horses.

OBJECTIVES: To determine the relationship between plasma lactate concentration and colonic viability and survival in horses with >or=360 degrees volvulus of the ascending colon. STUDY DESIGN: Retrospective study. ANIMALS: Horses (n=73) with >or=360 degrees volvulus of the ascending colon. METHODS: Medical records (January 2000-November 2005) of all horses examined for colic at Michigan State University Veterinary Teaching Hospital were reviewed. Horses were included only if plasma lactate concentration was measured preoperatively and a diagnosis of >or=360 degrees volvulus of the ascending colon was confirmed by surgery or necropsy. Non-survivors were only included if the ascending colon was evaluated histopathologically. Logistic regression analysis was used to model the relationship between lactate, colonic viability, and survival. RESULTS: Of 73 horses, 61 were discharged. Mean (+/-SD) plasma lactate concentration was significantly lower in survivors (2.98+/-2.53 mmol/L) compared with non-survivors (9.48+/-5.22 mmol/L; odds ratio [OR]=1.628, 95% confidence limit [CI]=1.259-2.105). Plasma lactate concentration was significantly lower in horses with a viable colon (3.30+/-2.85 mmol/L) compared with horses with a non-viable colon (9.1+/-6.09 mmol/L; OR=1.472, 95% CI=1.173-1.846). Plasma lactate concentration <6.0 mmol/L had a sensitivity of 84% and a specificity 83% for predicting horse survival. CONCLUSIONS: Our results demonstrate a strong association between plasma lactate concentration at the time of hospital admission and outcome in horses with >or=360 degrees volvulus of the ascending colon. CLINICAL RELEVANCE: Plasma lactate concentration may help predict colonic viability and horse survival after ascending colon volvulus in horses.

Cricothyroid muscle function and vocal fold stability in exercising horses.

OBJECTIVES: To determine (1) if the cricothyroid muscle had respiratory-related electromyographic (EMG) activity that increased with respiratory effort and (2) if bilateral cricothyroid myotomy resulted in vocal fold instability and collapse in exercising horses. STUDY DESIGN: Experimental. ANIMALS: Seven (3 EMG; 4 cricothyroid myotomy) Standardbred horses. METHODS: Three horses exercised on a treadmill at speeds corresponding to the speed that produced maximum heart rate (HR(max)), 75% of maximum heart rate (HR(75%max)), and 50% of maximum heart rate (HR(50%max)) for 60 seconds at each speed while EMG activity of the cricothyroid muscle and nasopharyngeal pressures were measured. Another 4 normal horses were exercised on the treadmill at HR(max) and HR(75%max) for 60 seconds at each speed before and after bilateral cricothyroid myotomy. Upper airway pressures were measured and videoendoscopic examinations were performed and videotaped at each speed. RESULTS: Peak phasic EMBG activity of the cricothyroid muscle was coincident with inspiration and increased with treadmill speed. Bilateral cricothyroid myotomy resulted in vocal fold collapse in all horses. Mean peak inspiratory pressures were significantly more negative compared with control values at both HR(max) and HR(75%max). CONCLUSIONS: Cricothyroid muscle dysfunction may be implicated in vocal fold collapse and likely causes inspiratory airway obstruction in exercising horses. CLINICAL RELEVANCE: Conditions compromising cricothyroid muscle function or motor innervation could result in vocal fold collapse.

The prevalence of laryngeal disease in a large population of competition draft horses.

OBJECTIVES: (1) To determine the effect of age, height, weight, breed, sex, and specific use on the prevalence of idiopathic left laryngeal hemiplegia (ILH) in a population of draft performance horses; (2) to determine the association between tracheal mucus and laryngeal dysfunction, and the prevalence of exercise-induced pulmonary hemorrhage (EIPH) in a population of draft performance horses. STUDY DESIGN: Cross-sectional. ANIMALS: Draft horses competing at the 2005 Michigan Great Lakes Draft Horse Show. METHODS: Endoscopic examinations were performed on horses competing at the 2005 Michigan Great Lakes Draft Horse Show. Signalment, height, and weight were obtained from the owners and trainers. RESULTS: Belgian, Percheron, and Clydesdale horses (n=183) were studied. Prevalence of ILH was 35%. Horse height was significantly associated with the risk of ILH in Belgian and Percheron horses but not Clydesdales. There was a significantly different prevalence of ILH among the breeds such that 42% Belgians, 31% Percherons, and 17% Clydesdales were affected. Laryngeal disease was a risk factor for increased tracheal mucus. None of the horses had acute evidence of EIPH. CONCLUSIONS: The prevalence of ILH in draft horses has increased or is higher in competition horses compared with previously studied groups. Tracheal and/or pulmonary inflammation may be more common in draft horses with ILH based on our findings that horses with ILH have more tracheal mucus than horses with normal laryngeal function. CLINICAL RELEVANCE: Selection pressure for large, taller, longer-necked horses may be responsible for a seemingly increased incidence of ILH in competitive draft horses.

Electromyographic activity of the hyoepiglotticus muscle and control of epiglottis position in horses.

OBJECTIVE: To determine whether the hyoepiglotticus muscle has respiratory-related electromyographic activity and whether electrical stimulation of this muscle changes the position and conformation of the epiglottis, thereby altering dimensions of the aditus laryngis. ANIMAL: 6 Standardbred horses. PROCEDURE: Horses were anesthetized, and a bipolar fine-wire electrode was placed in the hyoepiglotticus muscle of each horse. Endoscopic images of the nasopharynx and larynx were recorded during electrical stimulation of the hyoepiglotticus muscle in standing, unsedated horses. Dorsoventral length and area of the aditus laryngis were measured on images obtained before and during electrical stimulation. Electromyographic activity of the hyoepiglotticus muscle and nasopharyngeal pressures were measured while horses exercised on a treadmill at 50, 75, 90, and 100% of the speed that produced maximum heart rate. RESULTS: Electrical stimulation of the hyoepiglotticus muscle changed the shape of the epiglottis, displaced it ventrally, and significantly increased the dorsoventral length and area of the aditus laryngis. The hyoepiglotticus muscle had inspiratory activity that increased significantly with treadmill speed as a result of an increase in phasic and tonic activity. Expiratory activity of the hyoepiglotticus muscle did not change with treadmill speed in 4 of 6 horses. CONCLUSIONS AND CLINICAL RELEVANCE: Findings reported here suggest that contraction of the hyoepiglotticus muscle increases dimensions of the airway in horses by depressing the epiglottis ventrally during intense breathing efforts. The hyoepiglotticus muscle may be an important muscle for dilating the airway in horses, and contraction of the hyoepiglotticus muscle may induce conformational changes in the epiglottis.