An endoscopic and immunopathological study of respiratory tract disorders in thoroughbred racehorses

Much of the impetus for this research can be attributed to Kenneth W. Hinchcliff, who has studied exercise-induced pulmonary haemorrhage (EIPH) extensively. This thesis focused on EIPH in Thoroughbred racehorses competing in South Africa. Using tracheobronchoscopy, the prevalence and severity of EIPH and the association with racing performance was determined. Thereafter, the prevalence of other respiratory tract disorders and their association with racing performance is reported. This is followed by a study assessing interobserver variability using grading systems in the detection of respiratory tract disorders. Finally, there is a report on the immunopathogenesis of EIPH. Using tracheobronchoscopy after racing, the prevalence and severity of EIPH was assessed in 1,005 racehorses competing at high altitude (> 1,400 meters above sea level) and at sea level in a racing jurisdiction that does not allow the use of furosemide and nasal dilator strips. The prevalence and severity of EIPH was affected by altitude as racing at sea level was associated with a higher prevalence and greater severity of EIPH. Results also suggested that EIPH was associated with superior performance in South African Thoroughbred racehorses. Upper and lower respiratory tract disorders identified following tracheobronchoscopic examination included left arytenoid asymmetry, left laryngeal hemiplegia, epiglottic deformity, epiglottic entrapment, subepiglottic cysts, dorsal displacement of the soft palate, pharyngeal lymphoid hyperplasia (PLH), laryngeal and tracheal dirt, tracheal mucous (TM), tracheal stenosis and tracheal cartilage ring spikes in Thoroughbred racehorses after racing. Overall, there was a low prevalence of grade 2 and 3 arytenoid cartilage asymmetry, left laryngeal hemiplegia, epiglottic entrapment, subepiglottic cysts and epiglottic deformity, while more severe grades of PLH, laryngeal debris, tracheal debris, TM and tracheal cartilage ring spikes had a higher prevalence. An association with sex was identified as tracheal cartilage ring spikes occurred more often in male racehorses. Superior racing performance was identified in racehorses with grade 3 tracheal mucous and tracheal cartilage ring spikes. Endoscopic grading of EIPH, PLH, arytenoid cartilage movement (ACM), and TM was performed by 3 observers that were blinded to each racehorse’s identity and race day performance using previously established grading criteria. Excellent interobserver reliability was seen using the EIPH grading system, while the weighted kappa for PLH, ACM and TM was lower. The study demonstrated sufficient reliability for the use of the EIPH, PLH, ACM and TM grading systems in racehorses competing in South Africa. The study concluded that tracheobronchoscopy seemed to be a practical screening technique that may have prognosticative validity and clinical dependability and that would allow safe and quick assessment of the respiratory tract of a large number of racehorses in field conditions. Venous blood was collected from 10 horses in each EIPH grade classification (grade 0 to 4) following tracheobronchoscopic examinations for the determination of the presence and severity of EIPH. Following RNA isolation and cDNA synthesis, real-time PCR was used to detect equine cytokine-specific mRNA for interleukin (IL) -1, -6, -10, interferon (INF) -ã, and tumor necrosis factor (TNF) -á. Results of this study indicated that increased IL-6, and -10 mRNA production was associated with more severe forms of EIPH. Also, there was greater expression of IL-6 mRNA at sea level and TNF-á mRNA at high altitude. This study concluded that although it was unclear whether the inflammatory response observed in the study was due to pre-existing pulmonary inflammation or as a direct consequence of pulmonary bleeding, the study demonstrated a systemic correlation to pulmonary inflammation. The research reported in this thesis has contributed substantially to the determination of the prevalence, severity and affect on racing performance of respiratory tract disorders in Thoroughbred racehorses competing in South Africa. Also, determination of an association between EIPH and inflammation at a molecular level may assist future researchers in anti-cytokine therapies which may help reduce the prevalence and severity of EIPH.Thesis (PHD)--University of Pretoria, 2007.Companion Animal Clinical Studiesunrestricte

Causes of pleural effusions in horses resident in the UK

Pleural effusions (PE) reportedly occur most commonly secondary to bacterial pneumonia with neoplastic effusions contributing a minority of cases. The majority of reports originate from the USA and Australia, where long distance transport of horses, a recognised risk factor, may occur more frequently than in the UK. Anecdotally, a greater proportion of horses with PE are diagnosed with neoplasia in the UK than has been reported. The aim of this retrospective study was to describe the causes of PE in horses in the UK, and to identify markers that can help differentiate between septic and neoplastic causes of PE. Medical records from 4 equine hospitals in the UK were searched for horses diagnosed with PE. Information recorded included case background, admission physical examination and biochemical findings, and characteristics of the effusion (volume, cell count, total protein [TP] concentration). A total of 69 horses were identified, with 26 (38%) diagnosed with a neoplastic effusion. The remainder were categorised as septic, including 14/43 (32.5%) that had a history of international transport. Horses with septic effusions were significantly younger (8 vs. 13 years; P = 0.001) and had significantly smaller volumes of pleural fluid drained at admission (9.8 l vs. 32.2 l; P<0.001). Horses with septic PE had a significantly higher rectal temperature (38.6°C vs. 38.2°C; P = 0.03), fibrinogen concentration (7.8 g/l vs. 5.3 g/l; P = 0.01) and serum amyloid A concentration (230 mg/l vs. 59 mg/l; P = 0.02) than those with neoplastic effusions. Significantly higher pleural fluid cell count and TP concentration were identified in horses with septic PE (63.9 × 109/l vs. 8.6 × 109/l; P<0.001; 57.5 g/l vs. 35.9 g/l; P = 0.04). These results suggest that in the UK, neoplastic effusions account for a greater proportion of PE than previously reported. A large volume of PE in an older horse with a low cell count and relatively low TP concentration should increase the index of suspicion of neoplasia

Coagulation, oncotic and haemodilutional effects of a third-generation hydroxyethyl starch (130/0.4) solution in horses

REASONS FOR PERFORMING STUDY : Clinical indications for hydroxyethyl starches (HES) in horses include rapid plasma volume expansion and oncotic support during periods of hypoproteinaemia. Side effects such as coagulopathies associated with HES administration pose limitations to their use in veterinary medicine. In humans, tetrastarch [hydroxyethyl starch (130/0.4)] has demonstrated less profound effects on coagulation compared to 1st and 2nd generation HES. OBJECTIVES : To evaluate the haemostatic and oncotic effects of tetrastarch (130/0.4) administered at 10, 20 and 40 ml/kg bwt in healthy horses. Study design: Randomised crossover study design. METHODS : Tetrastarch (130/0.4) was administered to 6 healthy pony mares at 10, 20 and 40 ml/kg bwt with a 2-week washout period. Packed cell volume (PCV), total solids (TS), plasma colloid oncotic pressure (pCOP), platelet count and thromboelastography (TEG) was measured at baseline, immediately after infusion (0 h), 1, 6, 12, 24, 48, and 96 h after tetrastarch infusion. RESULTS : All TEG variables remained within normal reference ranges in all 3 treatment groups. Administration of tetrastarch at 40 ml/kg bwt resulted in a prolonged K-time (P=0.049) at 6 h post-infusion, and decreased maximum amplitude at 0 (P<0.001), 1 (P=0.022), 6 (P=0.006), 24 (P<0.001) and 48 h (P=0.013) postinfusion compared to baseline. Administration of tetrastarch increased mean pCOP values above baseline in all 3 treatment groups, persisting to 24, 6 and 48 h for the 10, 20 and 40 ml/kg bwt dose respectively. CONCLUSION : Although still within established reference ranges, compared to lower dosages, the administration of 40 ml/kg bwt tetrastarch (130/0.4) is more likely to induce changes in coagu lation as measured by TEG. Tetrastarch increased pCOP at all dosages evaluated in healthy horses.Faculty of Veterinary Science Research Fund ; Department of Companion Animal Clinical Studies, University of Pretoria ; and the Abe Bailey Trust.http://onlinelibrary.wiley.com/journal/10.1001/(ISSN)2042-33062015-11-30hb201

Exercise-induced pulmonary haemorrhage impairs racing performance in thoroughbred racehorses

REASONS FOR PERFORMING STUDY : Exercise-induced pulmonary haemorrhage (EIPH) occurs commonly in Thoroughbred racehorses worldwide. While EIPH is believed to be an important cause of impaired performance in these horses, there is limited evidence from sufficiently powered studies to evaluate this association. OBJECTIVES : To evaluate whether EIPH is associated with finishing position, distance finished behind race winners and differences in race earning among Thoroughbred horses racing in South Africa. STUDY DESIGN : Prospective cross-sectional study. METHODS : One thousand Thoroughbred horses racing in South Africa were enrolled prior to a single race and underwent tracheobronchoscopic examination within 2 h of racing. Three observers, blinded to the horses’ identity and race performance, independently evaluated EIPH occurrence and severity using video recordings of the examination. Data were analysed using multivariable logistic and linear regression while controlling for important horse and race factors as potential confounding variables. RESULTS : Overall, 68% of horses had evidence of EIPH (grade ≥1). Horses without evidence of EIPH (severity grade 0), when compared with horses with any evidence of EIPH (grade ≥1), were >2 times more likely to win races (odds ratio = 2.3; 95% confidence interval 1.4–3.7; P = 0.001), finished an average of one length ahead of horses with EIPH (P = 0.03), and were 2.5 times more likely to be in the highest decile in race earnings (odds ratio = 2.5, 95% CI 1.5–4.1, P<0.001). However, no association was identified regarding finishing in the top 3 positions or earning money when analysed as a continuous variable or analysed as any winnings vs. none. CONCLUSIONS : Exercise-induced pulmonary haemorrhage was associated with impaired performance in Thoroughbred racehorses not medicated with furosemide and not using nasal dilator strips. These findings provide strong corroboration of previous research indicating that the occurrence of EIPH has a major impact on the ability of Thoroughbred racehorses to compete successfully as elite athletes.Equine Research Centre, Faculty of Veterinary Science, University of Pretoria, and by the Thoroughbred Racing Trust of South Africa.http://onlinelibrary.wiley.com/journal/10.1001/(ISSN)2042-33062016-05-31hb201

Phenotypic characteristics of Hydrocephalus in stillborn Friesian foals

Hydrocephalus is uncommon in horses. However, in recent years, it has become clear that the prevalence of hydrocephalus is greater in Friesian horses than in other breeds probably due to their limited gene pool. Before identification of candidate genes that predispose to the development of hydrocephalus in Friesian horses can be pursued, an in-depth, phenotypic, pathological description of the condition in Friesians would be of great benefit. Our study aimed to characterize the morphology of hydrocephalus in Friesian horses, to support further investigation of the genetic background of this condition. Four stillborn Friesian foals with hydrocephalus were examined macroscopically and microscopically and compared with 2 normal stillborn Friesian foals without hydrocephalus. In all clinical cases, tetraventricular and venous dilatations were observed, together with malformation of the petrosal bone and, as a result, narrowing of the jugular foramen. These observations suggest a communicative hydrocephalus with a diminished absorption of cerebrospinal fluid into the systemic circulation at the venous sinuses due to a distorted, nonfunctional jugular foramen. This type of hydrocephalus is also recognized in humans and dogs and has been linked genetically to chondrodysplasia; this has already been recognized in dwarfism, which is another monogenetic defect in Friesian horses.http://vet.sagepub.com/am201

Prevalence of phayngeal, laryngeal, and tracheal disorders in thoroughbred racehorses, and effect on performance

Endoscopic examinations were performed on 1005 thoroughbred racehorses in South Africa a mean (sd) 24 (12·3) minutes after racing, to determine the prevalence of pharyngeal, laryngeal and tracheal disorders, and to determine the relationship of these disorders with performance (number of wins and placed finishes). Overall, there was a low prevalence of grade 2 and 3 laryngeal function (LF) (2·2 per cent), grade 4 LF (0·6 per cent), epiglottic entrapment (1·3 per cent), subepiglottic cyst (0·2 per cent) and epiglottic deformity (0·6 per cent), while a higher prevalence of grade 2 to 4 pharyngeal lymphoid hyperplasia (PLH) (63 per cent), laryngeal debris (43·5 per cent), tracheal debris (21·9 per cent), tracheal mucus (99·5 per cent) and tracheal cartilaginous nodules (TCNs) (6·8 per cent) was observed. Performance was not affected by the presence of epiglottic deformity, grade 2 and 3 LF, grade 4 LF, debris within the trachea or larynx, or epiglottic entrapment. Grade 3 PLH occurred in younger racehorses; performance was impaired in horses with grade 2 and 3 PLH. Furthermore, TCNs were more prevalent in male racehorses and were associated with better performance