Gaited horse research is limited, with the majority of the research focusing on the measurement of the temporal variables of adult-gaited horses. The objective was to measure the fore and hind limb kinematics of the flat-walking Tennessee Walking Horse (TWH) yearling. Four TWH yearlings were filmed at 60 Hz being led at a consistent flat walk that followed breed standards. Reflective markers attached along palpation points of the joint centres of the fore and hind limbs were tracked for five strides for each yearling. During stance, the elbow (154±3°), carpal (185±3°), fore (222±9 and 221±9°) and hind fetlocks (216±11°), hip (111±3°), stifle (157±4°) and tarsal (167±9°) joints demonstrated peak extension with the forelimb fetlock joint having double peaks of extension. During swing, the same joints demonstrated peak flexion with the elbow (109±3°) and hip (88±6°) peak flexion occurring later in the swing phase. The carpal (54±4°) joint demonstrated a greater range of motion than the tarsus (40±9°) with less vertical displacement. The hind fetlock (60±10°) had greater range of joint motion compared with the forelimb fetlock (45±8°), but lacked the double peak of extension during swing. Kinematic measurements will assist in objectively defining the gait for both clinical and performance applications.

This study used a randomized crossover design, with investigators blind to the treatment given, to test the hypothesis that seven commercially available electrolyte supplements would alter plasma concentrations of Na+, K+, Cl−, lactate, total protein (TP) and total carbon dioxide (tCO2) as well as plasma strong ion difference (SID) and haematocrit (HCT). Ten unfit Standardbred mares (∼450 kg, 4–9 years) completed a series of simulated race exercise tests (SRT) during which venous blood was collected at five sampling intervals (prior to receiving electrolyte treatment, prior to the SRT, immediately following exercise and at 60 and 90 min post-SRT). Plasma electrolyte and tCO2 concentrations were measured in duplicate using a Beckman EL-ISE electrolyte analyser. No difference (P>0.05) between treatments was detected at any of the five sampling intervals for plasma [Na+], [K+], [Cl−] or [tCO2]. Similarly, no significant difference was detected between treatments across each of the five sampling intervals for plasma SID, HCT or TP concentration. There were differences (P<0.05) in plasma [Na+], [K+] and [tCO2] (as well as plasma SID, HCT, and TP concentration) in the immediately post-SRT samples that were attributable to the physiological pressures associated with acute exercise. No differences (P>0.05) were detected between treatments across the pre-electrolyte and pre-SRT sampling intervals for plasma lactate concentration. There was, however, a significant time by treatment interaction during the 0, 60 and 90 min post-SRT sampling intervals for this parameter. The electrolyte supplements featured in this investigation did not affect either plasma tCO2 concentration or SID; however, this result does not rule out the potential for other supplements, especially those containing alkalinizing ingredients, to exert an effect that could push a horse towards threshold values.

The objective of the present study was to compare the hoof deceleration and ground reaction forces following impact on two different surfaces. Seven unshod Standardbreds were trotted by hand at 3.0–5.7 m s− 1 over a force plate covered by either of the two surfaces, sandpaper or a 1 cm layer of sand. Impact deceleration data were recorded from one triaxial accelerometer mounted on the fore- and hind hooves, respectively. Ground reaction force data were obtained synchronously from a force plate, sampled at 4.8 kHz. The differences between the two surfaces were studied by analysing representative deceleration and force variables for individual horses. The maximum horizontal peak deceleration and the loading rates of the vertical and the horizontal forces were significantly higher on sandpaper compared with the sand surface (P < 0.001). In addition, the initial vertical deceleration was significantly higher on sandpaper in the forelimb (P < 0.001). In conclusion, it was shown that the different qualities of the ground surface result in differences in the hoof-braking pattern, which may be of great importance for the strength of the distal horse limb also at slow speeds.

Pain, atrophy and dysfunction of the longissimus dorsi in the equine back can lead to poor performance and altered biomechanics. Back problems are often treated by manipulative therapy to this muscle. The purpose of this study was to identify if manipulative therapy resulted in changes to muscle tone or electromyographic (EMG) activity immediately after treatment. We measured the muscle tone during standing using a mechanical tissue indenter and the EMG activity (both at the T16 level in the longissimus dorsi) during walking around a figure-of-eight course in 26 horses. The horses were randomly assigned into three groups that received: (a) spinal (McTimoney) manipulations, (b) reflex inhibition therapy or (c) a control group that was not manipulated. The muscle tone and activity were measured immediately after treatment. Both the McTimoney and the reflex inhibition groups showed significant decreases in muscle tone (c. 12%) and walking EMG activity (c. 19%). The control group showed no significant change in tone or EMG activity. These results document how the longissimus dorsi muscle responds immediately after manipulative therapy. Further studies would be needed to identify how long such changes persist or if such changes caused a reduction in pain or an increase in performance.

The role of cardiac function or dysfunction in the pathogenesis of exercise-induced pulmonary hypertension and haemorrhage in horses has been minimally investigated. We hypothesize that pericardiotomy would enhance diastolic function and attenuate pulmonary vascular pressures in maximally exercising horses. Our objective was to evaluate diastolic function and cardiopulmonary pressures before and after pericardiotomy, at rest and at maximal exercise. Study design was both self- and externally controlled. Five horses underwent pericardiotomy after a baseline exercise test. They subsequently performed the same exercise protocol at 1 week and 13 weeks post-operatively. An external, unoperated control group of five horses performed the same experimental protocol. Pulmonary arterial pressure (PAP), pulmonary artery wedge pressure (PWP), right ventricular pressure, heart rate (HR) and oesophageal pressure were measured continuously at rest and at maximal exercise; maximum rates of ventricular pressure decrease (−dP/dtmax), relaxation half-time (t1/2), time constant of isovolumic relaxation (τ) and pulmonary capillary pressures (PcapP) were derived. Statistical analysis was performed using two-tailed Wilcoxon's signed-rank and rank-sum tests, with significance set at P<0.05. No significant differences were found in any variable after pericardiotomy was performed or between the experimental and external control groups. We conclude that during a 13-week study period, pericardiotomy does not alter pulmonary or ventricular pressures or rate of ventricular relaxation in the resting or maximally exercising horse. Results indicate that, in past and future studies requiring an open pericardium in normal horses, the cardiopulmonary parameters measured here are not affected by reduced pericardial pressure.

This study evaluated the effects of exercise on cardiac troponin I (cTnI) concentrations in healthy, adult horses.

Fifteen fit, healthy horses determined to have a normal cardiovascular system completed a standardized exercise test on a high-speed treadmill. Heparinized blood was collected for plasma cTnI concentrations before maximal exercise, and 1, 3, 6, 9, 12 and 24 h post-exercise. The cTnI concentrations were measured with a commercial system (Stratus CS, Dade Behring, Inc.). Results were analysed by a multivariate ANOVA, where indicated post hoc analysis was done by Tukey–Kramer HSD and significance was placed at p < 0.05.

All horses had elevations in cTnI concentrations after maximal exercise. Values for cTnI trended higher at 3 h (0.066 ± 0.011 ng ml− 1) and 6 h (0.062 ± 0.011 ng ml− 1) post-exercise compared with pre-exercise (0.039 ± 0.007 ng ml− 1), although this did not reach statistical significance. Mean cTnI concentrations were within our normal reference range at all time points, although four individuals were above our normal range after exercise.

These data show that short-term, high-intensity exercise induces a small rise in plasma cTnI in normal horses. This should be kept in mind when evaluating cTnI concentrations in horses that have recently completed intense exercise. In addition, these data suggest that 3–6 h after intense exercise may be the optimal time for measurement of cTnI concentrations in horses with suspected exercise-induced myocardial damage.

Impact-related peak decelerations with high loading rates are described as indicators of mechanical stress to the limb. The hoof deceleration pattern in the beginning of the stance phase has recently been described, together with ground reaction force measurements at slow speed; however, no information is available at high speeds. The objective of the present study was to investigate the hoof deceleration pattern following impact at slow speeds, comparable to earlier force plate studies, and at high speeds on a racetrack. Eight Standardbreds equipped with triaxial accelerometers mounted on fore- and hind hooves were driven from a jogcart on a harness-training racetrack with a stone dust surface at the mean speeds of 4.7, 5.7, 10.1 and 12.7ms−1. The accelerometer signals were sampled at 10kHz during 10s of constant speed along one straight of the racetrack. The signal was studied for each speed by the analysis of representative peak decelerations. At slow trot, the deceleration pattern was similar to what was found in earlier studies over the force plate. The peak values of both the vertical and horizontal decelerations increased significantly with a higher speed (P≤0.01). It was shown that a higher speed results in changes of the hoof deceleration pattern with higher peak decelerations. The maximum horizontal deceleration, together with the second vertical peak deceleration, were suggested to be major indicators on the mechanical stress subjected to the limb.