The purpose of this work is to investigate the effects of body mass (BM), velocity (V), and hoof shape on compressive surface strains in the wall of the front hoof at the trot. Toe angle (TA), heel angle (HA), toe length (TL), medial and lateral wall length (MWL, LWL) and BM were measured for nine adult, unshod Standardbreds. Five rosette gauges were glued around the circumference of the left forehoof of each animal which was then trotted on a treadmill at a set range of velocities from 3.5 to 7.5 m s−1. Analysis of variance (ANOVA) of principal compressive strains ɛ2 at midstance identified that all primary variables (BM, V, TA, HA, etc.) had a significant effect as did the interactions of TA×HA and BM×TA. These significant variables explained over 96% of the variation in ɛ2. Multiple regression of ɛ2 on these variables gave equations which accurately predicted ɛ2 within 3%, but the individual coefficients did not accurately describe how each variable affected ɛ2. Further tests using bivariate regression gave equations that enabled ɛ2 data to be standardized for BM and V at the gauge locations used here. Strain ɛ2 increased linearly with mass and curvilinearly with velocity (ɛ2∝V+V2), and both caused redistribution of strain to the dorsum and lateral quarter. Variation in each shape variable caused redistribution rather than simple increase or decrease in strains. The primary conclusion with regard to hoof shape is that the effects of change in any one measurement on strain magnitudes are affected by the values of all other measurements. Resolving the interplay among measurements in their effects on ɛ2 will need a considerably larger sample size than that used here.

The objective of this experiment was to compare the physiological changes that occurred in horses competing in the cross-country portion of Training, Preliminary and Intermediate horse trials. The hypothesis was that temperature (T), heart rate (HR), respiratory rate (RR), and on-site acid–base and electrolyte monitoring would allow differentiation between difficulty levels in horse trials. Sixteen client-owned horses competing at the Trojan-Horse Spring Horse Trials in Cave Creek, Arizona, USA, were studied. T, HR, RR and anaerobic lithium-heparinized jugular venous samples were obtained before, and 1–2 min after, cross-country exercise. Samples were analysed for blood gases (body temperature-corrected) and concentrations of sodium ([Na+]), potassium ([K+]), chloride ([Cl−]), ionized calcium ([Ca2+]i), blood urea nitrogen ([BUN]) and glucose ([GLC]) using a point-of-care analyser. Results were compared using analysis of variance with the level of significance set at P<0.05. In all groups, exercise increased T, HR, RR, packed cell volume and haemoglobin concentration, and decreased partial pressure of CO2 (PCO2), [total CO2 concentration], bicarbonate concentration ([HCO3−]) and [Ca2+]i (P<0.05). Post-exercise RR was higher, and pH, PCO2, [tCO2], [HCO3−] and base excess were lower, in Intermediate and sometimes Preliminary horses compared with Training horses (P<0.05). It was concluded that horse trials caused milder, but otherwise similar, physical, blood gas and electrolyte changes to those observed in complete three-day events. Physical and point-of-care plasma acid–base and electrolyte monitoring allowed differentiation between horses competing at various levels of difficulty in a horse trial.

In Standardbreds, the main aim of early training (begun during the growth period) is the mechanization of athletes leading to a particular gait called the ‘flying trot’. The present cross-sectional study was undertaken to investigate the biomechanical and physiological factors involved in this gait change, and aimed to analyse the effect of age on gait and energetic variables in a population of Standardbred horses under training. One hundred and forty-three horses aged from two to seven years were tested on a track at three speeds (8.5, 10 and 11.6 m s−1) with a gait-analysis system. Gait variables (temporal and linear variables, symmetry, regularity, two-beat rhythm, dorso-ventral, longitudinal and lateral activities) were compared between four age groups (two-, three-, four-, and five-year-olds and above). After a standardized exercise test, two energetic variables (V4 and V200) were also compared between these groups. Most variables were influenced by age/training status. The results indicated that, from young to mature racehorses, stride length and duration increase; and gait becomes more symmetric and more regular. We also observed a decrease in dorso-ventral, longitudinal and lateral activities, i.e. a decrease of thoracic displacements. These differences could be elucidated at slow speed and were still obvious at high speed. V4 and V200 also increased significantly with age/training status. All of these results indicate an improvement in co-ordination and a decrease in metabolic cost with increasing age/training status. Thus gait acquisition could be related to an improvement in trotting efficiency.

We studied the extent to which intra-articular hyaluronic acid (HA) administered to horses with experimentally induced synovitis in the third middle carpal joint altered cartilage proteoglycans (PGs) and the biomechanical properties of the third carpal bone. Intra-articular HA (Hylartin-V®) was administered to the middle carpal joints of healthy horses before and after the induction of synovitis by Escherichia coli lipopolysaccharide (LPS). Two groups of horses received intra-articular HA only, with evaluation 2 and 6 weeks later (group 2 and group 4). Two other groups (group 1 and group 3) received LPS followed by intra-articular HA and evaluation 2 and 6 weeks later. Ex vivo third carpal bone cartilage PG synthesis was measured by 35SO4 incorporation and third carpal bone cartilage PG content was determined by an assay for glucuronic acid. Biomechanical properties were measured by indentation testing. At the 2-week evaluation, HA did not ablate the quantitative reduction in PG synthesis and PG content in animals with experimental synovitis. However, by 6 weeks, there was a significant rebound effect in that PG synthesis and PG content were elevated in horses with experimental synovitis that had received intra-articular HA, compared with horses that had received HA only for that period of time. There were also alterations in the gel filtration profiles of newly synthesized PGs on Sepharose CL-2B among the groups. However, there were no de novo PG species associated with any of the treatments. Furthermore, we found that the biomechanical properties of third carpal bone cartilage were not altered in any of the groups. These studies showed that intra-articular HA administered to horses with experimentally induced synovitis did not provide short-term (i.e. 2-week) benefit to third carpal bone cartilage PG synthesis. However, a long-term benefit of intra-articular HA may occur after the acute effects of synovitis on PG synthesis and PG content subside.

The purpose of the present study was to determine the time course and magnitude of changes in extracellular and intracellular fluid volumes in relation to changes in total body water during prolonged submaximal exercise and recovery in horses. Seven horses were physically conditioned over a 2-month period and trained to trot on a treadmill. Total body water (TBW), extracellular fluid volume (ECFV) and plasma volume (PV) were measured at rest using indicator dilution techniques (D2O, thiocyanate and Evans Blue, respectively). Changes in TBW were assessed from measures of body mass, and changes in PV and ECFV were calculated from changes in plasma protein concentration. Horses exercised by trotting on a treadmill for 75–120 min incurred a 4.2% decrease in TBW. During exercise, the entire decrease in TBW (mean±standard error: 12.8±2.0 l at end of exercise) could be attributed to the decrease in ECFV (12.0±2.4 l at end of exercise), such that there was no change in intracellular fluid volume (ICFV; 0.9±2.4 l at end of exercise). PV decreased from 22.0±0.5 l at rest to 19.8±0.3 l at end of exercise and remained depressed (18–19 l) during the first 2 h of recovery. Recovery of fluid volumes after exercise was slow, and characterized by a further transient loss of ECFV (first 30 min of recovery) and a sustained increase in ICFV (between 0.5 and 3.5 h of recovery). Recovery of fluid volumes was complete by 13 h post exercise. It is concluded that prolonged submaximal exercise in horses favours net loss of fluid from the extracellular fluid compartment.

Routine study of three-dimensional (3D) tarsal kinematics is hampered by errors due to the displacement of skin surface-tracking markers relative to the underlying bones. Reliable kinematics can be obtained with bone-fixed markers, but an accurate, non-invasive method would have more applications. Simultaneous kinematic data from skin-based and bone-fixed markers attached to the tibia and third metatarsus were collected from three trotting subjects. The motion of the skin-based markers was extracted relative to the underlying bone motion tracked using the bone-fixed markers. The 3D skin displacement patterns for the skin-based markers were parameterized using a truncated Fourier series model. These displacements were expressed in terms of the local coordinate system for each bone. Skin displacement artefacts were observed in all three axes of each bone segment, with the largest displacements occurring at the proximal tibia. The mean skin displacement amplitudes in the tibia were 6.7%, 3.2% and 10.5% of segment length, and for the third metatarsus were 2.6%, 1.4% and 3.8% of segment length, for the craniocaudal, mediolateral and longitudinal segment axes, respectively. Skin displacement patterns could be expressed concisely using the Fourier series model. Displacements were also consistent between subjects, which should allow them to be used as a basis for developing a correction procedure for 3D tarsal joint kinematics.