Cardiac arrhythmias in poorly performing Standardbred and Norwegian-Swedish Coldblooded trotters undergoing high-speed treadmill testing.

The significance of cardiac arrhythmias and their possible association with upper airway obstruction are frequently considered in the clinical investigation of poor performance. The specific aims of this retrospective study of a group of poorly performing Standardbred and Norwegian-Swedish Coldblooded trotters were to: (1) describe the overall frequency and frequency distributions of arrhythmias; (2) describe arrhythmia characteristics including percent prematurity, relative recovery cycle lengths and QRS morphology; (3) describe variability of normal RR intervals; and (4) explore possible associations between upper airway abnormalities and arrhythmia categories during peak exercise and recovery. The records of 103 trotters presented to the Norwegian University of Life Sciences for high-speed treadmill testing were reviewed. The occurrence of at least one arrhythmic event was high (77-78%) when considering all exercise periods and 6-10% prematurity criteria. Triplets, salvos, and/or paroxysmal tachyarrhythmias occurred in 8% of horses during peak exercise. Complex ventricular arrhythmias occurred in 15% of horses in the first 2 min of recovery. Evaluation of QRS morphology and return cycle lengths demonstrated areas of overlap in characteristics typically attributed to either supraventricular or ventricular arrhythmias. There was no association between airway diagnosis and arrhythmias during any exercise period. The maximum average HR during peak exercise was an excellent predicter for complex ventricular arrhythmias during recovery. Because perfect categorization of arrhythmias is not possible, future studies should report descriptive arrhythmia information. Prospective studies that evaluate various degrees of upper airway obstruction and the effect on known initiators of arrhythmogenesis are needed.

Exploring the genetics underpinning dynamic laryngeal collapse associated with poll flexion in Norwegian-Swedish Coldblooded Trotter racehorses.

BACKGROUND: Dynamic laryngeal collapse (DLC) associated with poll flexion is the most common disorder of the upper respiratory tract (URT) in the Norwegian-Swedish Coldblooded Trotter (NSCT). The disorder, which has also been diagnosed in other breeds of trotters and gaited horses, appears to be related to anatomic phenotypes and only occurs during poll flexion when the horse is exercised 'on the bit'. OBJECTIVES: Identify genomic regions associated with DLC in the NSCT by combining a rigorous phenotyping protocol with genomic data from a high-density equine genotyping array. STUDY DESIGN: Prospective case/control study. METHODS: High-speed treadmill endoscopy was used to phenotype horses (n = 61) for DLC, distinguishing between cases and controls. Genome-wide association (GWA) analysis of DLC status was then performed using a principal component approach (PCA) with haplotype analyses subsequently performed for regions containing single-nucleotide polymorphisms (SNPs) above the suggestive genome-wide significance (GWS) threshold (P<1.0 × 10-5 ). RESULTS: One region containing 10 SNPs (Equus caballus chromosome [ECA] 7: 89,601,935-94,647,192) was above the suggestive GWS threshold. Two inferred haplotypes in this region demonstrated significant differences (P<0.001) between cases and controls, with the most frequent haplotype resulting in a significantly increased risk of DLC. MAIN LIMITATIONS: Small sample size as a result of stringent phenotyping protocols. CONCLUSIONS: The current study highlights a candidate genomic region on ECA7 as potentially important with regard to the manifestation of DLC. Further exploration of this region and the genes included within it will bring veterinarians and researchers closer to fully understanding the biological mechanisms underlying DLC in horses.

Histopathological assessment of intrinsic laryngeal musculature in horses with dynamic laryngeal collapse.

REASONS FOR PERFORMING STUDY: The pathogenesis of bilateral dynamic laryngeal collapse associated with poll flexion (DLC) of horses is unknown but might be associated with intrinsic laryngeal muscle weakness. OBJECTIVES: To investigate histopathological characteristics of the cricoarytenoideus dorsalis, the cricothyroid (CT) and the cricoarytenoideus lateralis muscles in DLC-affected horses and compare these with unaffected controls. Our hypotheses were that evidence of neurogenic atrophy of the CT or cricoarytenoideus dorsalis muscles would be found in DLC-affected horses and that observed changes would be symmetrically (left/right) distributed, or that muscle fibre diameter would be significantly reduced in DLC-affected horses compared to unaffected controls, reflecting an underlying paresis. STUDY DESIGN: Case-control study. METHODS: Five DLC horses and 8 controls were included. Muscle samples were harvested immediately following euthanasia. Fibre type proportions and size were evaluated by multiple immunofluorescence labelling of cryosections, and compared between sides (left/right) and groups (DLC-affected cases/ unaffected controls). Subjective and objective assessments of fibre type grouping were compared between sides and groups. RESULTS: Fibre type proportions, fibre size and the subjective assessment of fibre type grouping did not reveal any statistically significant differences between the groups. Objective assessment of fibre type grouping revealed significantly more large clusters of T1 fibres within the left cricoarytenoideus lateralis muscle of DLC-affected cases versus controls, and within the right CT muscle of control horses compared to the DLC-cases. CONCLUSIONS: The absence of bilateral symmetric fibre type grouping, fibre type loss and fibre atrophy in the DLC-affected cases do not support a neuromuscular component within the pathogenesis of DLC. The objective assessment of fibre type grouping revealed some statistical differences between the DLC-affected cases and the unaffected controls; however, these findings were inconsistent with regard to DLC. An alternative aetiology of DLC seems likely.

Surgical stress influences cytokine content in autologous conditioned serum.

REASONS FOR PERFORMING STUDY: No recommendations have been made regarding the relative timing of blood collection for autologous conditioned serum (ACS) preparation and surgical procedures. OBJECTIVES: 1) To identify effects of surgical stress on cytokine levels in ACS, 2) identify haematological markers for prediction of cytokine production in ACS and 3) investigate the necessity for specialised ACS containers when preparing a cytokine-rich serum. STUDY DESIGN: Experimental in vitro study. METHODS: Blood was drawn from 15 stallions admitted for elective castration preoperatively and 22-24 h post operatively and incubated in ACS containers and plastic vacutainer tubes containing Z Serum Clot Activator. Concentrations of interleukin (IL)-1 receptor agonist (IL-1Ra), IL-10, IL-1ß, tumour necrosis factor (TNF)-α, insulin-like growth factor (IGF)-1 and transforming growth factor (TGF)-ß were determined in all serum samples and compared between preparation methods and sampling time by ANOVA. Changes in cytokine levels induced by incubation, defined as delta cytokine, were calculated by subtracting the baseline levels from the levels in incubated samples. Based on post operative serum amyloid A (SAA), horses were grouped into 'mild', moderate' and 'marked' surgical stress; delta cytokine levels in post operative samples were compared between these groups by ANOVA. RESULTS: Delta IGF-1 was significantly lower in post operative samples compared with preoperative. Horses in the 'marked' surgical stress group had significantly lower delta IL-1Ra and delta TGF-ß than the 'moderate' group and significantly lower delta IGF-1 than the 'mild' group. No association between cytokine levels and haematology variables were identified. Cytokine levels were comparable between serum prepared in blood tubes and in specialised ACS containers. CONCLUSIONS: Surgical stress influences the cytokine content in ACS. Useful predictors of cytokine production in ACS were not identified. Specialised ACS containers may not be necessary for preparation of a cytokine-rich serum.

Results of upper airway radiography and ultrasonography predict dynamic laryngeal collapse in affected horses.

REASONS FOR PERFORMING STUDY: The pathogenesis of dynamic bilateral laryngeal collapse (DLC) associated with poll flexion is unknown. Diagnosis is dependent upon exercise endoscopy while replicating the flexed head position harness racehorses experience during racing. OBJECTIVES: To describe the effects of poll flexion on rostrocaudal laryngeal positioning and laryngeal lumen width in resting horses diagnosed with DLC compared to controls, and to establish diagnostic criteria for DLC by use of diagnostic imaging. STUDY DESIGN: Case-control study. METHODS: Fifty harness racehorses were prospectively included in the study: 25 cases diagnosed with DLC by treadmill endoscopy and 25 controls in which treadmill endoscopy revealed no abnormal findings. Laryngeal radiography and ultrasonography were obtained in neutral and flexed head positions. Laryngeal positioning and laryngohyoid conformation were compared between the groups and head positions. RESULTS: Poll flexion induced a greater rostral advancement of the larynx in relation to the hyoid apparatus in resting harness racehorses affected with DLC compared to controls (P = 0.007). At the level of the vocal folds, poll flexion resulted in a smaller laryngeal lumen width in horses affected with DLC compared to controls (P = 0.04). Horses were significantly more likely to be affected with DLC when the thyrohyoid bone to thyroid cartilage distance was ≥12 mm in poll flexion (odds ratio 21.3, 95% confidence interval 3.65-124.8, P = 0.004) and when laryngeal lumen width at the level of the vocal folds was less in poll flexion than in the neutral head position (odds ratio 8.4; 95% confidence interval 1.6-44.1, P = 0.012). CONCLUSIONS AND POTENTIAL RELEVANCE: In DLC horses, poll flexion advanced the larynx more rostrally and resulted in a decreased airway lumen width compared to control horses. Laryngeal ultrasound and radiography may facilitate the diagnosis of DLC at rest.

A novel treatment for dynamic laryngeal collapse associated with poll flexion: the modified checkrein.

REASONS FOR PERFORMING THE STUDY: Dynamic laryngeal collapse (DLC) associated with poll flexion is a performance limiting dynamic upper airway disorder commonly diagnosed in Coldblooded trotters. An inspiratory obstruction occurs when affected horses are driven with tension on the reins, inducing poll flexion. To date, surgical treatment and conservative management have failed to improve racing performance in affected horses. OBJECTIVES: To test the efficacy of an external device, the modified checkrein, in limiting poll flexion, diminishing laryngeal collapse and improving airway mechanics when horses are driven on a treadmill with tension on the reins and test the hypothesis that the modified checkrein will limit poll flexion thereby improving endoscopic appearance of the larynx and reduce airway obstruction in harness racehorses affected with DLC. METHODS: Fourteen Norwegian Coldblooded trotter (NCT) racehorses previously diagnosed with DLC associated with poll flexion exercised on a high-speed treadmill at speeds that resulted in heart rate >200 beats/min. Upper airway videoendoscopy recordings, tracheal pressures and video recordings of the head and neck position were collected while horses exercised with the conventional checkrein on Day 1 and the modified checkrein on Day 2. RESULTS: The modified checkrein successfully limited poll flexion as measured by no change in head position parameters between phases of no rein tension and phases of rein tension. Endoscopic scores were significantly improved (arytenoids cartilage collapse P<0.0001; vocal fold collapse P<0.0001) and tracheal peak inspiratory pressures were significantly less negative (P = 0.0162) when horses were fitted with the modified checkrein compared to the conventional checkrein. CONCLUSIONS AND POTENTIAL RELEVANCE: The modified checkrein successfully limited poll flexion and also prevented upper airway obstruction in NCT horses affected with DLC associated with poll flexion. The modified checkrein seems promising in offering a method of conservative management in harness racehorses affected with this disorder.

Relative prevalence of upper respiratory tract obstructive disorders in two breeds of harness racehorses (185 cases: 1998-2006).

REASONS FOR PERFORMING STUDY: Two genetically and phenotypically distinct horse breeds are used for harness racing in Scandinavia: the Standardbred (SB) and Coldblooded Trotter. These racehorses have identical environmental, management and racing conditions. Therefore, this study was undertaken to identify and compare the relative prevalence of upper respiratory tract (URT) obstructive disorders in these 2 breeds. OBJECTIVES: To determine whether these 2 phenotypically different breeds of harness racehorses have different predispositions for URT disorders. METHODS: Retrospective study of 88 Norwegian Coldblooded Trotters (NCT) and 97 SBs referred to this hospital for URT evaluation between 1998 and 2006. Case records of all horses diagnosed with an URT disorder during resting endoscopy, and all horses undergoing high-speed treadmill videoendoscopy (HSTV) with one or more periods of induced poll flexion were evaluated. The relative prevalence of URT disorders between the 2 breeds was analysed using a Fisher's exact test. RESULTS: There was a significant (P<0.05) breed predisposition regarding 6 URT disorders. Bilateral dynamic laryngeal collapse associated with poll flexion and flaccid epiglottis was significantly more frequent in the NCT. Alar fold collapse and nasopharyngeal collapse were significantly more frequent in SBs. Epiglottic entrapment and nasal flutter were only diagnosed in the SBs. Dynamic disorders were more common than resting disorders in both breeds. CONCLUSION: URT obstructive disorders (dynamic laryngeal collapse associated with poll flexion, flaccid epiglottis, pharyngeal collapse, alar fold collapse, nasal flutter and epiglottic entrapment) are breed related, indicating an anatomic or functional cause. Periods of induced poll flexion during HSTV was essential to declare harness racehorses free of URT disorders. POTENTIAL RELEVANCE: Further anatomic or physiological studies comparing these breeds could potentially provide insight into the pathogenesis of certain URT obstructive disorders. Induced poll flexion should be included in routine HSTV examinations of all harness racehorses.

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.

Retrospective study of the clinical features of limb cellulitis in 63 horses.

A retrospective study of 63 horses diagnosed with limb cellulitis between 1994 and 2005 was conducted. They all had an acute onset of painful, generalised limb swelling, and a clinical diagnosis of limb cellulitis was made by the attending clinician. None of the horses had more than one limb affected. Hindlimbs were significantly more often affected than the forelimbs (P<0.05). Thoroughbreds were significantly over-represented compared with the general distribution of breeds examined at the hospital. Blunt limb trauma, limb surgery and limb injections were associated with the cellulitis in most of the horses, but no plausible cause could be determined in 27 (43 per cent) of the cases. Staphylococcus aureus and Streptococcus species were frequently isolated, although mixed bacterial infections were also common. All the horses were treated with broad spectrum antimicrobials and non-steroidal anti-inflammatory agents, and ultrasound-guided surgical drainage was also applied in 14 cases. Fifty-six of the 63 horses (89 per cent) were discharged from the hospital. Laminitis affecting the contralateral limb was the most common reason for the euthanasia of the other seven horses.