Haemodynamic response to exercise in Standardbred trotters with red cell hypervolaemia

Validity of an established metabolic disorder index as a predictor for metabolic eliminations in endurance horses

Endurance horses are usually eliminated from the race due to lameness, metabolic ailments or technical reasons. The purpose of the study was to determine the validity and reliability of the metabolic disorder index (MDI) in predicting metabolic eliminations in endurance horses during an endurance race. Fifty-four endurance horses competing on two local endurance tracks were involved in the study. Blood samples were collected a day prior to the event to determine packed cell volume (PCV), chloride (Cl-), interleukin-6 (IL-6), creatine kinase (CK) and glutathione reductase (GR) concentrations from all participating horses. These parameters were used for the determination of metabolic disorder index in endurance horses at rest (one day before the competition). All data were statistically analysed. In 40, 80 and 120 km race distances, the successfully completed horses had a significant lower serum concentration of CK and a significant higher serum concentration of Cl- than the eliminated horses (P < .05). There were no significant differences in PCV, serum concentrations of IL-6 and GR between the successfully completed and eliminated horses in the 40, 80 and 120 km race distances. The MDI at the rest one day before the race could predict potential of metabolic eliminations in endurance horses with at least 78.26%, 80% and 83.33% accuracies in 40, 80 and 120 km race distances. The sensitivity of the MDI was 81.82%, 80% and 100% in the 40, 80 and 100 km race distances. The specificity of the MDI was 80% for the 80 km race distance and 75% for the 40 and 120 km race distances. In conclusion, the metabolic disorder index is a reliable method for the prediction of metabolic eliminations in endurance horses participating in endurance races.

Metabolic responses of acute phase protein, antioxidant and cytokine in Arabian Endurance horses

Changes in serum amyloid A (SAA), glutathione reductase (GR) and interleukin-6 (IL-6) could be responsible for the metabolic disorders and poor performance in Arabian horses during gruelling endurance events. Therefore, this study aims to evaluate the metabolic responses in relation to SAA, GR and IL-6 in Arabian horses during endurance events. After physical examination, the successfully completed (SC) (n=16) and eliminated-from-race (ER) (n=16) endurance horses were identified. The data obtained were analysed using ANOVA and pairwise correlations and the analysis were considered significant at P<0.05. There were significant differences between the SC and ER Arabian horses in haemoglobin (Hb), packed cell volume (PCV), creatine kinase, plasma protein, lactate and monocytes (P<0.0001), IL-6, GR (P<0.0007), SAA (P<0.0068), glucose (P<0.00342), aspartate transaminase (P<0.0049) concentrations. There were significant negative correlations between GR and plasma protein (r=-0.2830; P<0.0299) and GR and SAA (r=-0.2554; P<0.0489). There were significant positive correlations between IL-6 and Hb (r=0.2977; P<0.0220) and positive and not significant correlation between IL-6 and PCV (r=0.2449; P<0.0615). In conclusion, SAA, GR and IL-6 were significantly associated with metabolic crises in Arabian endurance horses. Therefore, SAA, GR and IL-6 could be used to evaluate performance and health status of endurance horses during training and endurance events.

Curriculum vitae paper - Sune G.B. Persson (1931-2009)

Sune Persson was born in Landskrona Sweden in 1931 and grew up on the west coast of Sweden. He graduated from the Royal Veterinary College in Stockholm in 1960 and in 1967 received his PhD entitled ‘On blood volume and working capacity in horses’. Sune pursued an academic career devoted to internal medicine and exercise physiology. He rapidly became Professor of Medicine in 1979 as the veterinary school moved from Stockholm to the Swedish University of Agricultural Sciences in Uppsala.

Myosin heavy chain-based fibre types in red cell hyper- and normovolaemic Standardbred trotters

An assumed link between red cell hypervolaemia, an excessive amount of training and impaired performance of hypervolaemic horses has led to a theory that the muscle fibres could be affected. Myosin heavy chain (MHC)-based fibre type composition in gluteus medius muscle of red blood cell normo- (NV) and hypervolaemic (HV) Standardbred trotters was evaluated using immunohistochemistry. Muscle biopsies were obtained from 13 NV and 16 HV horses. Serial transverse sections were cut and reacted with antibodies against different isoforms of the myosin heavy chains MHCI, MHCIIA and MHCIIX. Sections were also stained for myofibrillar ATPase pH 4,6 to identify types I, IIA and IIB, and NADH tetrazolium reductase to evaluate the oxidative capacity. The results show that types I and IIA fibres corresponded between staining methods, whereas IIB fibres in the ATPase stains were more numerous than pure MHCIIX fibres from immunohistochemistry. Many fibres identified histochemically as type IIB fibres contained both MHC isoforms IIA and IIX (MHCIIAX). Most fibres had a high oxidative capacity, but among the fibres within a section, the lowest was seen subjectively in pure MHCIIX fibres. Immunohistochemical stains make it possible to detect differences in fibre type composition that are not observed with myosin ATPase stainings, as it was found that HV horses had a lower percentage of MHCIIX fibres than NV horses. Immunohistochemical methods are, therefore, valuable for use in further research and clinical studies concerning muscle adaptations.

Gas exchange during intense exercise in Standardbreds with earlier Rhodococcus equi pneumonia

It is not known if pulmonary function and gas exchange during exercise are altered after pyogranulomatous pneumonia caused by Rhodococcus equi infection in the foal. The aim was to evaluate whether pulmonary gas exchange during high intensity exercise was altered in mature Standardbreds with a history of R. equi pneumonia as foals. In 7 foals, R. equi pneumonia was confirmed and treated. At age 3 years, when these horses were subjected to professional training, an inclined treadmill exercise test including 4 speeds was performed. Samples were collected when a steady state in VO2 was obtained. Red cell volume, heart rate, respiratory rate, and systemic and pulmonary mean arterial pressures were measured and cardiac output calculated. Oxygen and carbon dioxide tensions in arterial and mixed venous blood were analysed. The alveolar ventilation and the alveolar-arterial oxygen tension difference were determined. Pulmonary gas exchange was assessed and the ventilation-perfusion distribution, VA/Q, was estimated by the multiple inert gas elimination technique. Ventilation-perfusion mismatch and shunt were determined and diffusion limitation calculated. The gas exchange in Standardbred trotters previously infected with R. equi and successfully treated was not compromised during intense treadmill exercise compared with reference values for healthy, fit Standardbreds. We conclude that adult Standardbreds trotters with diagnosed R. equi pneumonia as foals, can achieve an adequate gas exchange at a workload close to VO2peak.

Effects of phlebotomy on haemodynamic characteristics during exercise in standardbred trotters with red cell hypervolaemia

Five Standardbred trotters with red cell hypervolaemia (RCHV) were compared before and after removal of approximately 22% (36 ml/kg bwt) of the total blood volume in order to evaluate the haemodynamic responses, haemorheological alterations and oxygen transport during exercise to fatigue. Data were recorded during submaximal exercise at 4 different speeds on a treadmill and then during continued running at the highest speed step until fatigue. Oxygen uptake (VO2), pulmonary artery pressure (PAP), systemic artery pressure (SAP), heart rate (HR), haematocrit and haemoglobin concentrations (Hb) were measured. Arteriovenous O2 content difference (C(a-v)O2), pulmonary vascular resistance (PVR) and total systemic resistance (TSR) were calculated. Whole blood and plasma viscosity and erythrocyte aggregation tendency were determined with a rotational viscometer. Endoscopy was performed after exercise. ANOVA was used for statistical analysis. Phlebotomy resulted in a decrease in haematocrit and Hb during the course of exercise. Blood and plasma viscosity were lower and erythrocyte aggregation tendency was higher after phlebotomy. Throughout exercise, including submaximal work and continued running to fatigue, PAP, SAP, PVR, TSR and C(a-v)O2 were lower after phlebotomy. HR was higher after phlebotomy during submaximal exercise. Oxygen delivery and VO2 were lower after phlebotomy in the period from submaximal exercise to fatigue. Run time to fatigue was shorter after phlebotomy. Four horses showed exercise-induced pulmonary haemorrhage (EIPH) before phlebotomy and the degree of bleeding was diminished but not abolished after phlebotomy. The reductions in PVR, TSR, PAP and SAP after phlebotomy were probably a result of reduced blood viscosity. In conclusion, although a 22% reduction in blood volume improved the haemodynamic and haemorheological parameters and the degree of EIPH, it was found that RCHV trotters have to rely on high oxygen delivery to the working muscles for maintenance of maximal performance.