Susan J. Holcombe

Effect of tracheal mucus and tracheal cytology on racing performance in Thoroughbred racehorses

REASON FOR PERFORMING STUDY Accumulations of mucus within the trachea are often found during endoscopic examinations of the airways of poorly performing racehorses, but the clinical importance of this finding is unknown. OBJECTIVES To determine the effect of tracheal mucus, pharyngeal lymphoid hyperplasia (PLH) and cytological indices of tracheal aspirate on racing performance in Thoroughbred horses assessed by race place and whether the horse was raced. METHODS Endoscopic examination of the nasopharynx, larynx and trachea was performed, and a tracheal aspirate obtained monthly at Thistledown racetrack from April to December, 2002 and 2003. Horses received a score of 0-4 for the degree of PLH and 0-4 for the amount of mucus visible in the trachea. The tracheal aspirate was assessed for turbidity, and total and differential cell counts. Generalised estimating equations models were used as repeated measures models for each risk factor and the level of association assessed through the risk factors P value in the model. RESULTS Moderate to severe tracheal mucus (2-4) was a risk factor for poor racing performance. There was no association between degree of PLH, cell counts or turbidity of tracheal wash fluid and racing performance. However, horses that raced had higher total neutrophil counts in tracheal wash aspirates than horses that did not race. CONCLUSIONS Grades 2-4 tracheal mucus should be considered a potential cause of poor racing performance in Thoroughbred horses. CLINICAL RELEVANCE Because moderate to severe tracheal mucus accumulation, and not increased tracheal neutrophils, was a risk factor for poor racing performance, functionally significant airway inflammation may best be confirmed by the presence of mucus rather than increased number of neutrophils in the trachea.

Effect of poll flexion and dynamic laryngeal collapse on tracheal pressure in Norwegian Coldblooded Trotter racehorses

REASON FOR PERFORMING STUDY Dynamic laryngeal collapse (DLC) associated with poll flexion is a newly diagnosed upper respiratory tract obstructive disorder that causes poor racing performance. OBJECTIVES To determine if Norwegian Coldblooded Trotters (NCTs) affected with DLC associated with poll flexion differ from normal, elite NCTs based on simple airway mechanics measurements. METHODS Five normal elite NCTs and 6 NCTs diagnosed previously with DLC underwent treadmill videoendoscopy while tracheal pressures were measured continuously. Alternating head positions were used such that horses were exercised with free head carriage and induced poll flexion at heart rates >200 beats/min. RESULTS Peak inspiratory tracheal pressures were significantly more negative for horses with DLC compared to the elite horses. This difference was only significant during the exercise phases when the poll region was flexed, P = 0.0015. Head position significantly affected peak inspiratory pressure for both elite and affected horses, P < 0.0001. CONCLUSIONS AND CLINICAL RELEVANCE Induced poll flexion significantly affected peak inspiratory pressure (PIP) in all horses; however, PIPs were significantly more negative in those affected with DLC. Based upon the tracheal pressure measurements recorded in this study, DLC in NCTs is a severe obstructive upper respiratory tract disorder that is induced by poll flexion.

Effects of stylopharyngeus muscle dysfunction on the nasopharynx in exercising horses

REASONS FOR PERFORMING STUDY Nasopharyngeal collapse has been observed in horses as a potential cause of exercise intolerance and upper respiratory noise. No treatment is currently available and affected horses are often retired from performance. OBJECTIVE To determine the effect of bilateral glossopharyngeal nerve block and stylopharyngeus muscle dysfunction on nasopharyngeal function and airway pressures in exercising horses. METHODS Endoscopic examinations were performed on horses at rest and while running on a treadmill at speeds corresponding to HRmax50, HRmax75 and HRmax, with upper airway pressures measured with and without bilateral glossopharyngeal nerve block. RESULTS Bilateral glossopharyngeal nerve block caused stylopharyngeus muscle dysfunction and dorsal nasopharyngeal collapse in all horses. Peak inspiratory upper airway pressure was significantly (P = 0.0069) more negative at all speeds and respiratory frequency was lower (P = 0.017) in horses with bilateral glossopharyngeal nerve block and stylopharyngeus muscle dysfunction compared to control values. CONCLUSIONS Bilateral glossopharyngeal nerve anaesthesia produced stylopharyngeus muscle dysfunction, dorsal pharyngeal collapse and airway obstruction in all horses. POTENTIAL RELEVANCE The stylopharyngeus muscle is probably an important nasopharyngeal dilating muscle in horses and dysfunction of this muscle may be implicated in clinical cases of dorsal nasopharyngeal collapse. Before this information can be clinically useful, further research on the possible aetiology of stylopharyngeus dysfunction and dysfunction of other muscles that dilate the dorsal and lateral walls of the nasopharynx in horses is needed.

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.

Incidence of Transfusion Reactions and Retention of Procoagulant and Anticoagulant Factor Activities in Equine Plasma

BACKGROUND The extent of preservation of clotting factors and incidence of transfusion reactions to noncommercial equine plasma is not documented. HYPOTHESIS Equine frozen plasma would retain its coagulation factor activity within the reference range and the incidence of transfusion reactions would be low. ANIMALS Ten plasma donor horses. Fifty clinically ill hospitalized horses receiving plasma were reviewed to determine the incidence of reactions. METHODS In vitro study and retrospective case review. Plasma was prepared by gravity sedimentation from whole blood refrigerated for 48 hours. The activities of factors VII through XII, antithrombin (AT), and Protein C were measured. Factor activities were compared for plasma samples obtained before blood collection (S0), after 48 hours of gravity sedimentation at 5 degrees C and after plasma separation (S1), and after 90 days of storage at -20 degrees C (S90). The medical records of 50 consecutive clinically ill horses receiving frozen plasma were reviewed to determine the incidence of transfusion reactions. RESULTS The combined effect of plasma harvest, gravity sedimentation, decantation, and freezing caused significant reductions in factors IX, (43%P= .0013), X, (33%P= .0001), XI, (48%P= .0008), AT, (10%P= .02), and Protein C (26%P= .0001). Activities for all factors analyzed, except factor X, remained within the reference ranges. Transfusion reactions were recorded for 5/50 horses. CONCLUSIONS AND CLINICAL RELEVANCE Clotting factors, AT, and Protein C were well preserved. The incidence of reactions to frozen plasma was 10%.

Prophylactic digital cryotherapy is associated with decreased incidence of laminitis in horses diagnosed with colitis

REASONS FOR PERFORMING THE STUDY Recent research suggested that prophylactic digital cryotherapy (ICE) improved lameness scores, diminished histological changes and early laminar inflammatory signalling in horses following oligofructose administration. In clinical practice, horses at risk for sepsis-associated laminitis receive ICE. Evidence to support this practice is lacking. OBJECTIVES To determine factors associated with development of laminitis in horses diagnosed with colitis, including ICE. STUDY DESIGN Multicentre retrospective case series. METHODS Medical records for horses admitted to 2 university hospitals diagnosed with colitis with evidence of systemic inflammatory response from 2002 to 2012 were reviewed. Horses were excluded if they exhibited signs of laminitis at admission, were ponies, miniature or draught breeds, or <2 years old. Data were analysed using univariate and multivariate logistic regression. RESULTS Twenty-seven of 130 horses (21%) developed laminitis. Seven of 69 (10%) horses treated with ICE developed laminitis compared with 20/61 (33%) horses that developed laminitis but did not receive ICE. Factors associated with laminitis included site of hospitalisation, admission respiratory rate (↑) and blood L-lactate (↑), and ICE (↓), P<0.05. Horses treated with ICE had 10 times less odds of developing laminitis compared with horses treated without ICE (odds ratio 0.11, 95% confidence limit 0.03-0.44). Sixteen horses (16/130, 12%) were subjected to euthanasia in hospital. Fourteen of these horses had laminitis and 2 did not develop laminitis. Survival for horses with colitis that developed laminitis was 13/27 (48%) compared with survival for horses with colitis that did not develop laminitis, 101/103 (98%). CONCLUSION Laminitis occurred in more clinically compromised horses. Use of ICE reduced the incidence of clinical laminitis in the study population suggesting that digital cryotherapy is an effective prophylactic strategy for the prevention of laminitis in horses with colitis.

Ethyl pyruvate diminishes the inflammatory response to lipopolysaccharide infusion in horses

REASONS FOR PERFORMING THE STUDY Endotoxaemia contributes to morbidity and mortality in horses with colic due to inflammatory cascade activation. Effective therapeutic interventions are limited for these horses. Ethyl pyruvate (EP), an anti-inflammatory agent that alters the expression of proinflammatory cytokines, improved survival and organ function in sepsis and gastrointestinal injury in rodents and swine. Therapeutic efficacy of EP is unknown in endotoxaemic horses. OBJECTIVES Determine the effects of EP on signs of endotoxaemia and expression of proinflammatory cytokines following administration of lipopolysaccharide (LPS) in horses. METHODS Horses received 30 ng/kg bwt LPS in saline to induce signs of endotoxaemia. Next, horses received lactated Ringers solution (LRS), (n = 6), 150 mg/kg bwt EP in LRS, (n = 6), or 1.1 mg/kg bwt flunixin meglumine (FM), (n = 6). Controls received saline followed by LRS (n = 6). Physical examinations, behaviour pain scores and blood for clinical pathological testing and gene expression were obtained at predetermined intervals for 24 h. RESULTS Lipopolysaccharide infusion produced clinical and clinicopathological signs of endotoxaemia and increased expression of tumour necrosis factor alpha (TNFα), interleukin 6 (IL-6) and IL-8 (P<0.001) compared with controls. Leucopenia and neutropenia occurred in all horses that received LPS. Horses treated with EP and FM had significantly (P<0.0001) reduced pain scores compared with horses receiving LPS followed by LRS. Flunixin meglumine was significantly more effective at ameliorating fever compared with EP. Both EP and FM significantly diminished TNFα expression. Ethyl pyruvate significantly decreased, but FM significantly increased, IL-6 expression. Neither EP nor FM altered IL-8 expression. CONCLUSIONS AND POTENTIAL RELEVANCE Ethyl pyruvate administered following LPS diminished the clinical effects of endotoxaemia and decreased proinflammatory gene expression in horses. Ethyl pyruvate suppressed expression of proinflammatory cytokines better than FM. However, FM was a superior anti-pyretic compared with EP. Ethyl pyruvate may have therapeutic applications in endotoxaemic horses.

Cationic and neutral amino acid transporter transcript abundances are differentially expressed in the equine intestinal tract

To test the hypothesis that AA transporter transcripts are present in the large intestine and similarly expressed along the intestinal tract, mRNA abundance of candidate AA transporter genes solute carrier (SLC) family 7, member 9 (SLC7A9), SLC7A1, SLC7A8, and SLC43A1 encoding for b(0,+)-type AA transporter (b(0,+)AT), cationic AA transporter-1 (CAT-1), L-type AA transporter-2 (LAT-2), and L-type AA transporter-3 (LAT-3), respectively, was determined in small and large intestinal segments of the horse. Mucosa was collected from the equine small (jejunum and ileum) and large intestine (cecum, left ventral colon, and left dorsal colon), flash frozen in liquid nitrogen, and stored at -80 degrees C. Messenger RNA was isolated from tissue samples, followed by manufacture of cDNA. Relative quantitative reverse transcription-PCR was conducted using the 2(-DeltaDeltaCT) method, with glyceraldehyde-3-phosphate dehydrogenase serving as the housekeeping gene. Compared with the jejunum, cationic and neutral AA transporter SLC7A9 mRNA abundance was similar in the ileum, cecum, and large intestinal segments. Compared with the jejunum, cationic AA transporter SLC7A1 mRNA abundance was similar in the ileum and decreased in the cecum, left ventral colon, and left dorsal colon (P < 0.001). Neutral AA transporter SLC7A8 mRNA abundance decreased from the cranial to caudal end of the intestinal tract (P < 0.001). Neutral AA transporter SLC43A1 mRNA abundance was similar in the ileum and left dorsal colon and increased in the cecum (P < 0.01) and left ventral colon (P < 0.1) compared with the jejunum. Cationic and neutral AA transporter SLC7A9 mRNA abundance was similarly expressed in the large compared with small intestine, whereas cationic AA transporter SLC7A1 was of low abundance in the large intestine; neutral AA transporters SLC7A8 and SLC43A1 were differentially expressed with decreased abundance of SLC7A8 and increased abundance of SLC43A1 in the large intestine. Results indicate that the large intestine might contribute to both cationic and neutral AA uptake and absorption predominantly via transporters LAT-3 and b(0,+)AT.

The effect of uterine torsion on mare and foal survival: a retrospective study, 1985--2005.

REASONS FOR PERFORMING STUDY Anecdotal speculation suggests that prognosis for survival of mares and foals following correction of uterine torsion has improved over the past 30 years. OBJECTIVES To determine statistically the outcome of uterine torsion according to duration of clinical signs, stage of gestation, parity, physical examination findings, method of correction, prognosis for survival and reproductive health of the mare, and prospects for the foal within the neonatal period. METHODS This retrospective study combined cases from 4 equine referral hospitals. RESULTS The stage of gestation at which uterine torsion occurred was a risk factor for survival of mare and foal. Overall mare survival was 53/63 (84%); when uterine torsion occurred at < 320 days gestation, 36/37 (97%) of mares survived compared to 17/26 (65%) survival rate when uterine torsion occurred at > or = 320 days gestation. Overall foal survival was 54% (29/54). When uterine torsion occurred at < 320 days gestation, 21/29 (72%) foals survived compared to 8/25 (32%) when uterine torsion occurred at > or = 320 days gestation. Thirty mares were discharged from the hospital carrying a viable fetus following uterine torsion correction and 25/30 (83%) of these mares delivered live foals that survived beyond the neonatal period. CONCLUSIONS Prognosis for survival for mares and foals following uterine torsion is good and improves if torsion occurs < 320 days compared to > or = 320 days gestation. CLINICAL RELEVANCE Gestational timing of uterine torsion should be considered when advising clients about the prognosis for survival of the mare and foal. The prognosis for a mare delivering a live foal is good if the mare is discharged from the hospital following uterine torsion correction with a viable fetus.

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.