J. P. Valette

Sub-clinical diseases affecting performance in Standardbred trotters: diagnostic methods and predictive parameters.

The objectives of this study were to determine the prevalence of sub-clinical diseases in poorly-performing Standardbred horses, compare their physiological response to exercise with control horses, and identify predictive parameters of poor-performance. Fifty horses underwent thorough clinical and ancillary examinations, including haematological and biochemical evaluation, Doppler echocardiography, standardised exercise tests (SETs) on both treadmill and racetrack, treadmill video-endoscopy and collection of respiratory fluids. Most of the poorly-performing horses exhibited many concomitant diseases. The most frequently diagnosed problems involved the lower and upper respiratory tract and the musculoskeletal system. Poor-performers had lower speeds at a blood lactate (LA) concentration of 4mmol/L (V(LA4)) and a heart rate (HR) of 200bpm (V(200)) on treadmill and racetrack, as well as lower values for haematological parameters, plasma angiotensin-converting enzyme and antioxidants, compared to control horses. Problems of the respiratory system were the most frequently diagnosed sub-clinical diseases affecting performance. SETs, together with some blood markers, may be useful as a non-specific diagnostic tool for early detection of diseases that may affect performance.

Effects of a synthetic all-weather waxed track versus a crushed sand track on 3D acceleration of the front hoof in three horses trotting at high speed.

REASONS FOR PERFORMING STUDY Inadequate track surfaces are believed to be a risk factor in the occurrence of musculoskeletal injuries, but quantification of the shocks and vibrations provoked by hoof impact on different ground surfaces (including new synthetic tracks) has been insufficiently documented in trotters under high-speed training conditions. OBJECTIVES To test the reliability and sensitivity of an accelerometric device to discriminate between the biomechanical effects of 2 different tracks at high speed. METHODS Three French Trotters were used and their right front hooves were equipped with one triaxial accelerometer. Two different track surfaces (crushed sand track: S and all-weather waxed track: W) were tested when horses were trotting in a straight line. For each session of measurements, trials were repeated 3 times in a Latin square design. The speed of the runs was set at 10 m/s, controlled by the driver and recorded synchronously. Sample rate was set at 6 kHz. Acceleration of the hoof (resultant vector and 3D components), power spectral density at impact and variability (between strides, trials, sessions and horses) were analysed. Statistical differences were tested using a GLM procedure (SAS). Least square mean differences were used for comparisons between tracks (P < 0.05). RESULTS Results showed that the deceleration of the hoof (magnitude of the resultant vector) was statistically different between the 2 tracks with an attenuation of the shock of about 50% on the all-weather waxed track. Magnitude of the power spectral density was reduced at higher frequencies on W. CONCLUSIONS AND CLINICAL RELEVANCE These preliminary results demonstrate the sensitivity of the tool to discriminate between the different behaviours of the hoof on the different track surfaces at high speed. Deceleration and vibration of the hoof at impact were reduced on W compared to S, suggesting a better shock-absorbing quality of this track.

The effects of treadmill inclination and speed on the activity of two hindlimb muscles in the trotting horse

Electromyographic activity (EMG) was used to determine how hindlimb muscle activation patterns vary with speed and incline in the horse. EMG was recorded using surface electrodes over the gluteus medius and tensor fasciae latae muscles during treadmill locomotion at trot for different combinations of speed (3.5 to 6 m/s) and inclination (0, 3 and 6%). Raw EMG signals were processed to determine stride duration, activity onset and end, and integrated EMG (IEMG). Stride and stance phase duration decreased linearly with increasing speed. Stride duration was not influenced by the slope. Onset and end of muscle activity came significantly earlier in the stride cycle when speed increased and later when inclination changed from 0 to 6%. The relative duration of the burst (percentage of stride duration) increased as running speed increased, but tended to decrease with increasing slope. The IEMG of the muscles increased with increasing speed and slope, the largest increase being observed in the tensorfasciae latae. It is concluded that both increases in speed and inclination lead to an increase in the integrated electromyographic activity and hence to a higher workload of the 2 hindlimb muscles investigated.

The effects of treadmill inclination and speed on the activity of three trunk muscles in the trotting horse.

The purpose of this study was to evaluate the effects of speed and slope on the activity of trunk muscles. The electromyographic (EMG) activity of the splenius (Sp), longissimus dorsi (LD) and rectus abdominis (RA) muscles was recorded with surface electrodes during treadmill locomotion at trot for different combinations of speed (3.5 to 6 m/s) and slope (0 to 6%). Raw EMG signals were processed to determine activity duration, onset and end and integrated EMG (IEMG). For the 3 muscles investigated, onset and end of activity were obtained earlier in the stride cycle when speed increased. A longer duration of activity for the LD, a shorter duration for the RA and an unchanged duration for the Sp were also observed. The IEMG of the latter was poorly affected by speed, whereas it increased linearly with speed for the 2 other muscles. When treadmill inclination changed from 0 to 6%, EMG activity of the LD and RA began and ended later; a longer activity duration was noted. Temporal parameters for Sp did not change with slope. A significant and progressive increase in the IEMG of the 3 muscles was observed with increasing slope. This evaluation of the activity of trunk muscles provides objective data for the use of speed or slope in training programmes.

Use of a 3D dynamometric horseshoe to assess the effects of an all-weather waxed track and a crushed sand track at high speed trot: Preliminary study

REASONS FOR PERFORMING STUDY Track surface quality is considered a risk factor of musculoskeletal injuries. Ground reaction force (GRF) measurement is a relevant approach to study the interaction between the hoof and the ground. Force plates are not adapted to compare different surfaces at high speed. A 3D dynamometric horseshoe (DHS), using 4 triaxial piezoelectric sensors, has been developed and validated. OBJECTIVES To use the DHS to compare the effects of 2 track surfaces, an all-weather waxed track and a crushed sand track, on the GRF in trotter horses under training conditions. METHODS The right forelimb of 3 French Trotters was equipped with the DHS. Two tracks were tested in a straight line: a crushed sand track (S) and an all-weather waxed track (W). For each session, trials were repeated 3 times in a Latin square design. The speed of the runs was set at 10 m/s and recorded synchronously. For each trial, data acquisition was performed at 600 Hz and 10 consecutive strides were analysed. Statistical differences were tested using a general linear model procedure. RESULTS The amplitude of the maximal longitudinal braking force (Fx) was significantly lower on W compared to S. This event happened about 6% later in the stance phase on W. The magnitude of the GRF at impact decreased on W. The average speed and the mean stance phase duration were not statistically different on both surfaces. The stride length was about 6 cm longer on S. CONCLUSION AND POTENTIAL RELEVANCE This study demonstrates the ability and sensitivity of the DHS to discriminate track surfaces by measuring the GRF at high speed. These preliminary results show that the loading rate, the amplitude of horizontal braking and shock at impact are attenuated on W, which suggests a reduction of stresses in the distal limb.

Use of linear and non-linear functions to describe the growth of young sport- and race-horses born in Normandy.

The objectives of this study were to establish standards for growth and to model the evolution of wither height (WH) between birth and adult age in different breeds of sport- and race-horses. Therefore, 398 foals, then yearlings of three different breeds, were measured regularly between birth and 18 months of age. Linear and non-linear functions were compared for describing the growth in each breed group. The monomolecular, Gompertz, logistic and cubic models correctly estimated WH in the three breeds during the first 2 years (R2 = 0.99, s.e. 3.9 to 4.5) and better than the cubic and quadratic models (R2 = 0.93, s.e. = 4.7 to 5.3). The logarithmic and power model seemed better in the last part of the growth period (2 to 6 years, R2 = 0.85, s.e. = 5.6 to 5.9). The linear model did not fit with data on most of the growth period. Comparison of the growth in the three breeds using these models confirmed that race-horses had an intense growth in their first months whereas sport-horses had a more regular growth prolonged in their first years of life.

Evolution of some biochemical markers of growth in relation to osteoarticular status in young horses: results of a longitudinal study in three breeds

Osteocalcin (OC), bone fraction of alkaline phosphatases (BAP) and hydroxyproline (HOP) are markers of bone cell activity. The kinetics of these markers and the analysis of their variations could be related to the osteoarticular status (OAS) of young horses. The growth of Thoroughbreds, French Trotters and Selle Francais horses was fol- lowed up to 18 months. Blood samples were taken regularly to measure OC, HOP and BAP by standardized tech- niques. The OAS was evaluated by radiographic examination of the limbs. Based on radiographic findings, two groups of horses were investigated, with no lesions or severely affected. Analysis of variance was used to detect the effects of age and breed, and OAS on parameters. The logarithmic model was used to determine the kinetics of the markers. A rapid decrease in marker concentrations with age and differences between breed was observed. At birth, BAP, OC and HOP concentrations were significantly higher in normal horses (1910 UI l 21 , 192 ng ml 21 and 35 mg l 21 , respectively) than in horses with severe lesions (1620 UI l 21 , 149 ng ml 21 and 24 mg l 21 , respectively). During the first 6 months, OC, HOP and BAP remained lower in severely affected horses.

Biomechanical analysis of hoof landing in horses trotting at high speed and the effects of ground surfaces

Excessive and repetitive loadings are thought to induce injury to the distal limb (Radin 1999). Therefore, the phase of rapid loading following initial contact of the hoof with the surface is thought to be important for the orthopaedic health of the horse (Johnston and Back 2006). Shock and vibration during hoof impact on different ground surfaces have already been measured. The biomechanical analysis of hoof landing combining kinematics of the hoof, 3D deceleration, 3D forces and CoP has not been investigated yet during high-speed exercise in the field condition because of the technical issues of such challenging conditions. As the events during this initial phase of the stance are believed to be modified by track surfaces, these have been incriminated in the induction of injurious loading and movement. Hypothesis can be made that the properties of different ground surfaces can alter the kinetic and kinematic patterns of hoof landing. The aim of the present study is to describe the mechanism of hoof landing in the trotting horse at high speed and to evaluate the effects of different ground surfaces on this phenomenon.Recent numerical studies of abdominal aortic aneurysm (AAA) suggest that intraluminal thrombus (ILT) may reduce the stress loading on the aneurysmal wall. Detailed fluid structure interaction (FSI) in the presence and absence of ILT may help predict AAA rupture risk better. Two patients, with varied AAA geometries and ILT structures, were studied and compared in detail. The patient specific 3D geometries were reconstructed from CT scans, and uncoupled FSI approach was applied. Complex flow trajectories within the AAA lumen indicated a viable mechanism for the formation and growth of the ILT. The resulting magnitude and location of the peak wall stresses was dependent on the shape of the AAA, and the ILT appeared to reduce wall stresses for both patients. Accordingly, the inclusion of ILT in stress analysis of AAA is of importance and would likely increase the accuracy of predicting AAA risk of rupture.

A method for quantifying vertical displacements of the trunk and gait symmetry in horses trotting at high speed

Evaluation of trunk movements is an interesting parameter for quantifying gait symmetry in the horse. The trot is a symmetric gait in which two diagonal stance phases (right frontlimb/left hindlimb (LH) and left frontlimb/right hindlimb (RH)) are following each other and spaced by a suspension phase. During one stride, the withers and the croup are moving downward and then upward during each diagonal stance. Evaluation of gait symmetry in the horse mainly relies on the comparison of the vertical displacements of those anatomical points. Because of the great economical loss due to lameness and the difficulties in establishing a diagnosis, techniques of lameness quantification have been a research priority (Audigié et al. 2002). Biomechanical studies traditionally employ optical motion capture systems for the determination of the position of an object in a room-based coordinate system. This constrains experiment to the calibrated volume of the camera system. Only a few strides may be collected per “trial” and this kind of system is not well suited for outdoor experiments at high speed on a racetrack. The objective of this study was to develop a system allowing the objective measurement of back mobility and gait symmetry in horses trotting at high speed in racing condition.

LE PROJET SEQUISOL: ÉVALUATION BIOMÉCANIQUE DE L'EFFET DES SOLS ÉQUESTRES SUR L'APPAREIL LOCOMOTEUR DU CHEVAL

The quality of ground surfaces conditions equine locomotion and can be a risk factor for osteoarticular and tendinous lesions. A novel protocol of biomechanical measurements has been developed to characterize the effects of ground surfaces on the locomotor system and locomotion of harnessed trotter horses under training conditions. This protocol is based on the simultaneous use of a 3D dynamometric horseshoe, a 3D accelerometer, a superficial digital flexor (SDF) tendon force ultrasonic sensor, inertial measurement units, and a high-speed camera. Three French trotters were used to compare two tracks at the Grosbois training centre (crushed sand and all-weather waxed track) ; biomechanical measurements were performed at a standardized speed (9.7 m/s, i.e. 35 km/h). The all-weather waxed track appeared as the most damping (shock absorbing), i.e. lesser impact deceleration and braking force and lesser maximal loading rate of the SDF tendon. However, the horse’s locomotor comfort (determined by the stride length) did not seem to be greater. The preliminary results of the tests performed since October 2006 as part of the Sequisol project (10 tracks tested on 5 different sites) confirm superior shock-absorbing properties as well as a “slower” characteristic during the braking phase for the all-weather waxed tracks, and generally speaking, the strong influence of maintenance conditions of the surfaces on the biomechanical results.