Heart rate and blood lactate responses during the cross-country test of 2-star to 5-star eventing competitions

The objective of this retrospective study was to evaluate the physiological demands of cross-country competitions at different levels. Heart rates (HR) and post exercise blood lactate concentrations (LAC) measured between 2010 and 2019 in response to 1,463 cross-country competitions (437 at 2-star, 703 at 3-star, 313 at 4-star and 10 at 5-star level) in 294 horses were analysed. The effect of competition level, mean velocity, height profile, total distance, number of jumping efforts, climate, age, sex, percentage of Thoroughbred blood and performance level on HR, LAC, HR recovery and LAC disappearance rates was evaluated by Linear Mixed Effects Models. Mean HR and LAC significantly increased from 2-star to 4-star level (P<0.001). Each 30 m/min increase in mean velocity was associated with a 3 beats/min increase in HR (P<0.001) and a 41% increase in LAC (P<0.001) and each 30 m increase in cumulative elevation with a 2 beats/min increase in HR (P<0.001) and a 32% increase in LAC (P<0.001). Each 20 m increase in mean distance per jumping effort was associated with a 1 beat/min decrease in HR (P<0.01) and a 13% decrease in LAC (P<0.001). Compared to Warmbloods, horses with 75% Thoroughbred blood had 4 beats/min lower HRs (P<0.05) and 34% lower LAC values (P<0.001). Each 5 years increase in age was associated with a 4 beats/min decrease in HR (P<0.001, only in mares) and an 11% decrease in LAC (P<0.01). The HRs during the first 3 minutes of recovery were higher at warmer and more humid conditions (P<0.05). The rate of LAC disappearance was higher in horses with higher percentages of Thoroughbred blood (P<0.05).

Correlation of competition performance with heart rate and blood lactate response during interval training sessions in eventing horses

Objective performance monitoring in eventing horses is rare as the implementation of standardised exercise tests is commonly perceived to interfere with the daily training routine. The validity of performance parameters derived from GPS data, heart rate (HR) and post exercise blood lactate concentration (LAC) measured during usual training sessions should therefore be evaluated. Velocity (V), HR and post exercise LAC recorded during 172 interval training sessions in 30 horses were retrospectively analysed. Linear regression of HR, averaged over retrospectively defined speed ranges, was used to calculate the V at HRs of 150 (V150) and 200 (V200) beats/min. A single exponential regression model, fitted to LAC in relation to HR values from the whole group of horses, was used to predict LAC for each horse’s individual HR value and to calculate the difference between measured and predicted LAC (LACdiff). Recovery HRs were derived from bi-exponential regression of HR decrease after exercise. Results were compared between different stages of training in the same horses and between horses categorised as superior (SP) and average performer (AP) according to their competition performance. V150 and V200 significantly increased with progressing training. SP had higher V150 and V200 values, lower LACdiff values and lower HRs after 1 min of recovery (HRR60s) than AP. Competition performance was positively correlated to V150 and V200 but negatively correlated to LACdiff and HRR60s. Regular monitoring of HR and LAC in response to interval training provided valuable indicators of performance. The results of this study may contribute to an increased applicability of routine performance monitoring in eventing horses.

Cardiovascular, respiratory, gastrointestinal and behavioral effects of intravenous lidocaine in healthy, conscious horses and evaluation of the relationship with lidocaine and monoethylglycinexylidide serum concentrations

This study aimed to evaluate the relationship between the serum concentrations of lidocaine/ monoethylglycinexylidide (MEGX) and their effects on several systems in horses. Five healthy, conscious horses received a two-hour placebo intravenous infusion followed by a two-hour lidocaine infusion (bolus of 1.3 mg/kg over ten minutes followed by a continuous rate infusion of 0.05 mg/kg/min). Lidocaine and MEGX serum concentrations were sampled every ten to fifteen minutes during the experiment, and the presence of muscle fasciculations and loss of balance as well as the respiratory, digestive and cardiovascular systems of the five horses were evaluated by means of different non-invasive methods. During the lidocaine infusion, the mean (± SD) lidocaine and MEGX concentrations were respectively 768.88 ± 93.32ng/ml and 163.08 ± 108.98 ng/ml. The infusion of lidocaine significantly influenced the presence of fasciculations, caused a statistically but non-clinically significant decrease of systolic and diastolic blood pressures, which were both correlated with lidocaine and MEGX serum concentrations, and it increased the duodenal contractions frequency, which was correlated with the serum lidocaine concentration. In this study, mild hypotensive and prokinetic effects of short-term lidocaine infusion were observed.

Mitochondrial function and aerobic capacity assessed by high resolution respirometry in Thoroughbred horses

During the initial stages of training of young Thoroughbred horses, low intensity exercise is employed to increase aerobic capacity. High Resolution Respirometry (HRR) allows the determination of aerobic capacities in small samples of permeabilised muscle fibres. The aim of the study was to measure the mitochondrial function by HRR in Thoroughbred horses, to compare these values to Warmblood horses and to evaluate the effect of a 10-weeks training period. The mitochondrial function was measured by HRR using different substrate-uncoupler protocols (SUIT 1 and 2) in muscle microbiopsies from two groups of untrained horses: 17 Warmblood and 8 Thoroughbred and in the group of 8 Thoroughbred horses before and after a 10-week training period. The SUIT1 protocol employed to compare the two groups of horses showed that in Thoroughbred horses, the mean values for oxygen flux expressed as tissue mass-specific respiration were significantly higher for complex I (CI)Glutamate+Malate, CI + complex II, and maximum electron transport capacities (ETSmax) than the mean values measured in Warmblood horses. The SUIT 1 and SUIT 2 protocols revealed large differences among Thoroughbred horses before and after training. The SUIT 2 protocols showed a significant difference for the complex I activity before and after training but only when the oxygen flux was expressed as percentage of ETSmax. This study shows the interest of HRR in equine sport medicine and exercise physiology, but shows that the technique requires further refinement. Indeed significant differences have been shown between the Thoroughbred and the Warmblood horses highlighting the need to have baseline data for each breed. The Thoroughbred horses had globally a high oxidative phosphorylation capacity with an increase of CI activity induced by an aerobic training program.

Age-dependent expression of osteochondrosis-related genes in equine leukocytes

INTRODUCTION

Osteochondrosis (OC) is a developmental disease in horses which has a significant impact on the horse's welfare and performance. The early disturbance in the process of endochondral ossification progresses to inflammatory and repair processes in older horses. Previously, differentially expressed genes in leukocytes of OC-affected horses have been identified. The aim of the present study is to detect age-related changes in these differentially expressed genes.

MATERIALS AND METHODS

The expression of OC-related genes was analysed by real-time PCR and subsequent statistical analysis (ΔΔCT) in the leukocytes of 135 Belgian Warmblood horses divided into three different age groups: <12 months (n=47), 18-24 months (n=50) >30 months (n=38).

RESULTS

Relative expression of genes of horses less than 12 months of age showed significant induction of the genes MGAT4A, PRKCG, MHCI, ApoB, ApoB3G, B4GALT6 and a significantly lower expression of the genes OAS3. Horses of 18-24 months of age, showed a significantly higher expression of the genes TBC1D9, MGAT4A, IFIH1, MHCIIa and MMP1. Horses of more than 30 months of age showed a significantly higher expression of the genes MGAT4A, HP, SECTM1 compared with their age-matched control groups.

CONCLUSIONS

The study demonstrates that OC-related genes are differentially expressed in horses of different ages compared with their age-matched controls. Some of the genes may be implicated in cell signalling and differentiation as well as carbohydrate and lipid metabolism and inflammation. However, the causal relationship between the differentially expressed genes and the development and progression of the OC lesions needs to be determined.

159 EFFECTS OF EMBRYO TRANSFER IN A LARGER BREED ON POSTNATAL GROWTH AND GLUCOSE METABOLISM IN HORSES

In equids, the size of the uterus determines fetal intrauterine development, which in turn affects postnatal insulin sensitivity and growth rate. We induced intrauterine growth enhancement through embryo transfer using Pony (P), Saddlebred (S), and Draft (D) horses and studied growth and insulin sensitivity in foals from birth to one year of age. Control pregnancies of S-in-S (n = 14) and P-in-P (n = 10) were obtained by AI. Enhanced fetal growth was obtained by transferring S (S-in-D, n = 7) and P embryos (P-in-D, n = 5) into D mares. From birth to weaning (180 days), each foal was kept with its surrogate P, S, or D dam. At 3, 140, and 380 days, glucose clearance and pancreatic beta cell response to exogenous glucose were assessed with an intravenous glucose tolerance test (IVGTT). At 200 days, the euglycemic-hyperinsulinemic clamp method was used to determine the sensitivity and responsiveness of tissues to exogenous insulin. Plasma T3, T4, and IGF1 were assayed at 3 and 180 days. Data were analysed using one-way ANOVA and Tukey post hoc tests. S-in-S were heavier and taller than P-in-P from birth to 380 days (P < 0.001). Before weaning, plasma concentrations of several hormones involved in growth were lower in S-in-S than P-in-P (at 3 and 180 days, respectively, T3: P = 0.08 and P = 0.02, T4: P < 0.001 and P = 0.06, IGF1: P = 0.04 and P < 0.001). No difference was found in glucose regulation between these groups. In contrast, post-weaning insulin resistance was observed in P-in-P at 200 days (P < 0.001) and confirmed at 380 days where they exhibited slower glucose clearance (P = 0.03) associated with higher fasting glucose (P < 0.001) than S-in-S. Fetal growth was not enhanced in S-in-D with no difference in height and weight at birth. Although S-in-D grew faster from 30 to 140 days, growth rates were not different from S-in-S after weaning, weaning coinciding with lower T3 (P < 0.001) in S-in-D than in S-in-S. Glucose regulation was not different between the two groups, but insulin remains to be assayed at 140 and 380 days. Fetal growth was enhanced in P-in-D: at birth, they were heavier (P = 0.01) and taller (P < 0.001) than P-in-P. Growth of P-in-D was faster until weaning. No more difference, however, was observed between P-in-D and P-in-P at 380 days. Plasma concentrations of T3 (P = 0.03) and those of T4 (P < 0.001) were lower at 3 days and T3 was still lower at 180 days (P < 0.001) in P-in-D compared with P-in-P. Moreover, P-in-D developed early insulin resistance: insulin secretion was higher in P-in-D compared with P-in-P (P = 0.002) after IVGTT at 3 days. At 200 days, however, P-in-D and P-in-P had the same sensitivity to insulin. There was no difference in glucose clearance rates at 380 days, but P-in-D had lower fasting glucose (P < 0.001) than P-in-P. Insulin assays at 140 and 380 days are pending. In conclusion, these data indicate that transfer of a small breed embryo into a large breed mare and subsequent suckling by the recipient mare can enhance fetal and postnatal growth and affect the foal’s glycaemia and sensitivity to insulin at birth and in subsequent months. Ongoing work includes analyses of milk samples and effects on general health.

Relationship between exercise-induced systemic inflammatory like reaction and racing performance in endurance horses

Endurance race induces a rise of serum creatine kinase (CK) activity and a systemic inflammatory like response characterised by an increase of neutrophil counts, plasma and muscle myeloperoxidase (MPO) and elastase (ELT) concentrations in horses. Horses performing the same standardised exercise test do not respond with the same magnitude of inflammatory reaction. The aim of the present study was to measure the total neutrophil count, the ratio neutrophil:lymphocyte, the MPO and ELT plasma concentrations and concomitant increases of serum CK activities in competing endurance horse and to relate these results to their race performance. Twenty one horses participating in a 120 km 4 star endurance race recruited on a voluntary basis finished the race with a mean speed ranging from 13.1 to 19.8 km/h. Blood was taken the day before the race and two hours after the race. Mean values of neutrophil counts, ratio neutrophil:lymphocyte, plasma MPO and ELT concentrations and serum CK activities after the race were significantly higher than the pre-race values. There was no correlation between neutrophil counts, MPO, ELT or CK and the mean speed of the horses during the race except for the ratio neutrophil:lymphocyte where a significant negative correlation was observed. These results showed that systemic responses induced by strenuous exercise such as an endurance race is not clearly related to performance but also to horse-related factors, such as intrinsic capacity or training.

Exercise and pharmacological stress echocardiography in healthy horses

REASONS FOR PERFORMING STUDY

Stress echocardiography could be a useful diagnostic test in horses suspected to suffer from exercise-induced myocardial dysfunction as a cause of exercise intolerance.

OBJECTIVE

To evaluate the effect of treadmill exercise and pharmacological stress test on left ventricular echocardiographic parameters.

METHODS

Echocardiography was performed in 2 groups of 5 healthy horses, either immediately after a near-maximal treadmill exercise (Group EXE) or during a pharmacological challenge (Group DOB) consisting of 35 microg/kg atropine, followed by incremental dobutamine infusion rates of 2-6 microg/kg bwt/min for 5 min duration each, which led to a cumulative dobutamine dose of 100 microg/kg. Left ventricular M-mode parameters were compared at rest and at heart rates of 80, 100, 110, 120 130, and 140 beats/min, within each group.

RESULTS

In 2 horses of Group EXE, echocardiographic measurements were impossible at 140 and 130 beats/min, as their heart rates dropped too fast in the immediate post exercise period. In the remaining 3 horses image quality was not always satisfactory at heart rates of 130 and 140 beats/min. Systolic left ventricular parameters and fractional shortening measured at 130 and 140 beats/min were significantly different from values obtained at lower heart rates. Horses in Group DOB reached expected heart rates of 80 and 100 beats/min, after the administration of atropine and during a dobutamine infusion rate of 2 microg/kg bwt/min, respectively. Heart rates targets of 110, 120, 130, and 140 beats/min were reached at mean (+/- s.d.) dobutamine infusion rates of 2.8 +/- 0.4, 3.2 +/- 0.4, 4.0 +/- 0.7, 5 +/- 0.7 microg/kg bwt/min, respectively. Systolic left ventricular parameters and fractional shortening at heart rates of 110, 120, 130, and 140 beats/min, were significantly different from values obtained at lower heart rates.

CONCLUSION

The pharmacological stress test induced changes in ventricular dimensions at heart rates of 80 to 140 beats/min. Using this test, high quality images can easily be obtained at heart rates of 140 beats/min. Conversely, in post exercise echocardiography, obtaining good quality images at heart rates of 130 and 140 beats/min is difficult, which limits use of the technique in routine clinical settings.

POTENTIAL RELEVANCE

Further studies should demonstrate the potential of pharmacological stress test as a diagnostic tool in horses suffering from exercise-induced myocardial dysfunction.

The use of radial extracorporeal shockwave therapy in the treatment of urethral urolithiasis in the horse: a preliminary study

BACKGROUND

Radial extracorporeal shockwave therapy (ESWT) is widely used in equine practice for the treatment of orthopedic problems. However, its original use as a lithotripsy device in human and canine urology led us to postulate that it could be used as an alternative to the surgical treatment of urethral calculi in horses.

HYPOTHESIS

Radial ESWT can easily and safely fragment calculi in the distal urethra of the horse.

ANIMALS

Two postmortem cases and 1 live case of obstructive urinary disease admitted at the Veterinary Teaching Hospital of Liege.

METHODS

A radial shockwave device was directly applied to the urethra in an attempt to fragment calculi. An ex vivo trial was performed on the same retrieved calculi to investigate pressure settings in order to obtain complete fragmentation of the calculus.

RESULTS

In all cases, radial ESWT was able to fragment the calculus partially, enabling retrieval of the remaining fragments via the urethra. Much higher pressure settings than those used for in vivo partial fragmentation were necessary to obtain complete destruction of the calculi ex vivo.

CONCLUSIONS AND CLINICAL IMPORTANCE

This brief report suggests the use of radial ESWT as a safe and useful alternative to more invasive surgical management of urethral calculi in horses.

Tetanus in the equine species: a retrospective study of 31 cases

BACKGROUND

Few studies exist about factors affecting the outcome of horses with tetanus.

ANIMALS

31 equids (30 horses and 1 donkey) with a clinical diagnosis of tetanus admitted to the Equine Clinic of the University of Liege between 1991 and 2006. The cases were divided into two groups according to the outcome (survivors and non-survivors).

METHODS

The clinical data of survivors and non-survivors were compared using an ANOVA (continuous data) or a Fisher's test (discrete data).

RESULTS

The survival rate was 32%. Most animals were 5 years or younger, and none had been appropriately vaccinated. The non-survivors were significantly younger than the survivors. The development of dyspnoea, recumbency, and the combination of dysphagia, dyspnoea, and recumbency was observed significantly more in the non-survivors than in the survivors. The timing of tetanus antitoxin administration (either immediately after the onset of suggestive signs or after a delay) was not different between the two groups. The time between the occurrence of a wound and the first signs ranged from 2 days to 2 months and was not significantly different between groups. All non-survivors died within 8 days of the first signs.

CONCLUSIONS & CLINICAL IMPORTANCE

This study suggests that young animals are affected more often and more severely by tetanus than older animals. Dyspnoea, recumbency, and the combination of dysphagia, dyspnoea, and recumbency can be considered as indicators of a poor prognosis in equids suffering from tetanus.

Determination of lidocaine and its two N-desethylated metabolites in dog and horse plasma by high-performance liquid chromatography combined with electrospray ionization tandem mass spectrometry

A sensitive method for the quantification of lidocaine and its metabolites, monoethylglycinexylidide (MEGX) and glycinexylidide (GX), in animal plasma using high-performance liquid chromatography combined with electrospray ionization mass spectrometry is described. The sample preparation includes a liquid-liquid extraction with methyl tert-butylmethyl ether after addition of 2M sodium hydroxide. Ethylmethylglycinexylidide (EMGX) is used as an internal standard. For chromatographic separation, an ODS Hypersil column was used. Isocratic elution was achieved with 0.01 M ammonium acetate and acetonitrile as mobile phases. Good linearity was observed in the range of 2.5-1000 ng ml(-1) for lidocaine in both dog and horse plasma. For MEGX, linear calibration curves were obtained in the range of 5-1000 ng ml(-1) and 20-1000 ng ml(-1) for dog and horse plasma, respectively. In dog and horse plasma good linearity was observed in the range of 200-1500 ng ml(-1) for GX. The limit of quantification (LOQ) in dog plasma for lidocaine, MEGX and GX was set at 2.5 ng ml(-1), 20 ng ml(-1) and 200 ng ml(-1), respectively. For horse plasma a limit of quantification of 2.5 ng ml(-1), 5 ng ml(-1) and 200 ng ml(-1) was achieved for lidocaine, MEGX and GX, respectively. In dog plasma, the limit of detection (LOD) was found to be 0.8 ng ml(-1), 2.3 ng ml(-1) and 55 ng ml(-1) for lidocaine, MEGX and GX, respectively. In horse plasma the LOD's found for lidocaine, MEGX and GX, were 1.1 ng ml(-1), 0.5 ng ml(-1) and 13 ng ml(-1), respectively. The method was shown to be of use in pharmacokinetic studies after application of a transdermal patch in dogs and after an intravenous infusion in horses.

p65 Homodimer activity in distal airway cells determines lung dysfunction in equine heaves

Nuclear factor-kappaB (NF-kappaB) activity, which is a key regulator of inflammatory gene expression, is increased in bronchial epithelial cells from horses suffering from heaves (a hypersensitivity-associated inflammatory condition of the lung). To determine whether this increased activity extends to distal airways and to other pulmonary cells, cells recovered by broncho-alveolar lavage (BAL) in healthy and heaves-affected horses were assessed for NF-kappaB activity. NF-kappaB activity was much higher in BAL cells from heaves-affected horses, especially during crisis (disease exacerbation), than in cells from healthy horses. Moreover, the level of NF-kappaB activity found in BAL cells was positively correlated to total lung resistance and to the proportion of neutrophils present in BAL fluid. Finally, prototypical p65-p50 NF-kappaB heterodimers were absent from BAL cells, which mostly contained p65 homodimers. These results (1) show that increased NF-kappaB activity is a general feature of heaves lung; (2) demonstrate the importance of p65 homodimers in neutrophilic inflammation; and (3) suggest that the use of specific NF-kappaB inhibitors could improve lung function in heaves-affected horses.