Reliability of surface electromyographic (sEMG) measures of equine axial and appendicular muscles during overground trot.

The reliability of surface electromyography (sEMG) has not been adequately demonstrated in the equine literature and is an essential consideration as a methodology for application in clinical gait analysis. This observational study investigated within-session, intra-subject (stride-to-stride) and inter-subject reliability, and between-session reliability of normalised sEMG activity profiles, from triceps brachii (triceps), latissimus dorsi (latissimus), longissimus dorsi (longissimus), biceps femoris (biceps), superficial gluteal (gluteal) and semitendinosus muscles in n = 8 clinically non-lame horses during in-hand trot. sEMG sensors were bilaterally located on muscles to collect data during two test sessions (session 1 and 2) with a minimum 24-hour interval. Raw sEMG signals from ten trot strides per horse and session were DC-offset removed, high-pass filtered (40 Hz), full-wave rectified, and low-pass filtered (25 Hz). Signals were normalised to peak amplitude and percent stride before calculating intra- and inter-subject ensemble average sEMG profiles across strides for each muscle and session. sEMG profiles were assessed using waveform similarity statistics: the coefficient of variation (CV) to assess intra- and inter-subject reliability and the adjusted coefficient of multiple correlation (CMC) to evaluate between-session reliability. Across muscles, CV data revealed that intra-horse sEMG profiles within- and between-sessions were comparatively more reliable than inter-horse profiles. Bilateral gluteal, semitendinosus, triceps and longissimus (at T14 and L1) and right biceps showed excellent between-session reliability with group-averaged CMCs > 0.90 (range 0.90-0.97). Bilateral latissimus and left biceps showed good between-session reliability with group-averaged CMCs > 0.75 (range 0.78-0.88). sEMG profiles can reliably describe fundamental muscle activity patterns for selected equine muscles within a test session for individual horses (intra-subject). However, these profiles are more variable across horses (inter-subject) and between sessions (between-session reliability), suggesting that it is reasonable to use sEMG to objectively monitor the intra-individual activity of these muscles across multiple gait evaluation sessions at in-hand trot.

Swing phase kinematic and kinetic response to weighting the hind pasterns.

REASONS FOR PERFORMING STUDY: It is considered that specific exercises to strengthen limb musculature would be helpful. OBJECTIVE: To describe swing phase kinematic and kinetic changes in the hindlimbs of trotting horses in response to the addition of leg weights to the hind pasterns. METHODS: Six horses were prepared by placing reflective skin markers on the hindlimbs, the withers and fore hooves. Horses were evaluated at trot for 6 trials with and without leg weights (700 g) attached around the pasterns, with the 2 conditions applied in random order. The markers were tracked to determine peak heights of the flight arc of the hind hooves and swing phase joint angulations. Inverse dynamic analysis was used to calculate positive and negative work done across each joint in the first and second halves of the swing phase. Comparisons between conditions were made using paired t tests (normally distributed data) or the Wilcoxon rank-sum test (non-normally distributed data). RESULTS: Peak height of the flight arc of the hind hooves was significantly higher with leg weights as a result of increased flexions of the stifle, tarsal and metatarsophalangeal joints. Increased positive (concentric) work was performed by the hip and tarsal musculature to protract and raise the limb in early swing, then to retract and lower the limb in late swing. Increased negative (eccentric) work was performed across the stifle and metatarsophalangeal joints to control their movements in response to increases in inertia and momentum due to the weights. CONCLUSIONS: The addition of weight to the hind pasterns stimulates increased muscular activity across all the hindlimb joints from the hip to the metatarsophalangeal joint. CLINICAL SIGNIFICANCE: The addition of weight to the hind pasterns may have therapeutic applications in activating and strengthening the hindlimb musculature. This is particularly relevant in the hip region, which appears more sensitive and responsive to the effect of weights than to tactile stimulation alone.

Hindlimb response to tactile stimulation of the pastern and coronet.

REASONS FOR PERFORMING STUDY: Lightweight tactile stimulators attached to the hind pasterns increase the height of the hind hoof flight arc but details of the induced changes in swing phase kinematics and kinetics have not been investigated. HYPOTHESES: Stimulators on the hind pasterns are associated with increased hindlimb joint flexions and increased positive work performed by the hip and tarsal musculature. MATERIALS AND METHODS: Nine nonlame horses trotted 4 times with and without 55 g tactile stimulators loosely attached around the hind pasterns. Height of the flight arc and peak flexion angles of the hindlimb joints were measured and net positive and negative work performed across each joint during the swing phase were calculated using inverse dynamics analysis and compared across paired conditions. RESULTS: Speed and stride duration did not change but stimulators were associated with a reduction in hind stance duration. The flight arc was higher with stimulators due to increased flexions of the stifle, tarsal, metatarsophalangeal and distal interphalangeal joints. Positive work increased in the tarsal musculature, but not in the hip musculature, and negative work increased across the stifle, metatarsophalangeal and distal interphalangeal joints. POTENTIAL RELEVANCE: The effects of tactile stimulation of the hind pasterns on joint motion and muscle activation may be used in physiotherapy and rehabilitation to restore or increase flexion of the hindlimb joints with the exception of the hip joint. The ability to stimulate concentric activity of the tarsal musculature may have therapeutic applications in conditions such as toe dragging.

Trunk deformation in the trotting horse.

REASONS FOR PERFORMING STUDY: Estimates of the position of the centres of mass (CM) of body segments are usually extrapolated relative to bony landmarks as determined in cadaver studies. This extrapolation assumes that segments are rigid bodies. Since the trunk represents a large percentage of the total body mass in horses, violation of the rigid body assumption by the trunk segment has important consequences for studying the biomechanics of equine locomotion. OBJECTIVES: To assess the magnitude of error in CM position due to deformability of the trunk segment and the timing of these errors during the trotting stride. The hypothesis was that shape changes during a stride are repeatable and predictable. METHODS: Forty skin markers were attached in a grid pattern on the trunks of 6 adult horses, with an additional marker attached to each hoof. The markers were tracked using an 8 camera motion analysis system. Each horse was tested at 10 different velocities during trotting. The CM of the trunk was calculated under the assumption of a rigid body, based on 5 spine markers and from the volume encompassed by the 40 markers. The difference between the 2 calculation methods quantifies the effect of trunk deformation on the position of the CM. RESULTS: The trunk changed shape during locomotion in a repeatable manner resulting in cyclic changes in CM position. Amplitudes of the CM displacement due to trunk deformation were equal in magnitude in the transverse and longitudinal directions. In the vertical direction, the CM moved only at half the amplitude. Magnitudes were strongly horse-dependent. CONCLUSIONS AND POTENTIAL RELEVANCE: Shape changes in the equine trunk segment in the horizontal plane should be taken into account when modelling locomotion of horses. Amplitudes are horse dependent, complicating the development of correction routines.

Effects on behaviour and rein tension on horses ridden with or without martingales and rein inserts.

Unsteady hand position can cause discomfort to the horse, potentially leading to conflict behaviours (CB) such as head tossing or tail lashing. Some instructors feel that martingales or elastic rein inserts can reduce discomfort caused by inexperienced and unsteady hands. Others consider these devices to be inappropriate 'crutches'. Four horses and nine riders were tested under three conditions in random order: plain reins, adjustable training martingales (TM), and elasticised rein inserts (RI). Rein-tension data (7s) and behavioural data (30s) were collected in each direction. Rein-tension data were collected via strain-gauge transducers. Behavioural data were assessed using an ethogram of defined behaviours. No differences in the number of CB were observed. Mean rein tension for TM was higher than that of RI or controls. Relative to the withers, the head was lower for horses ridden with martingales. Carefully fitted martingales may have a place in riding schools that teach novices.

Lesions associated with the use of bits, nosebands, spurs and whips in Danish competition horses.

BACKGROUND: Information is needed to guide sport administrators in formulating rules for equipment use in competitions. OBJECTIVES: To seek associations between spurs, bits, nosebands and whips with injuries in horses during competitions in four equestrian sports. STUDY DESIGN: Cross sectional study. METHODS: Post competition evaluations were performed in 3143 horse/rider combinations competing in Danish Equestrian Federation competitions in dressage, showjumping, eventing and endurance by trained evaluators who recorded the presence and type of spurs, bits, nosebands, and whips. Further evaluations recorded noseband tightness, (in three categories <2 cm, 2-3 cm, >3 cm), the presence of hair or blood on spurs; hair loss, lesions or blood on the ribcage behind the girth; abrasions and/or blood at the commissures of the lips; and swelling, lesions or blood on the forequarters or hindquarters. Statistical analysis was performed to determine relationships between discipline (dressage, showjumping, eventing, endurance), level of competition (level 0-7), type/tightness of equipment, and prevalence of injuries. RESULTS: The presence of hair (3.2% of horse/rider combinations) and blood (0.4% of horse/rider combinations) on spurs were highly associated. Longer spurs and lower competition levels were significantly associated with hair on the spurs and worn hair on the horse's ribcage. Oral lesions or blood were visible at the commissures of the lips in 9.2% of horses and increased with level of competition but did not differ between bit types or bitless bridles. Looser upper noseband category was associated with decreased risk of oral lesions (odds ratio [OR] 0.66, 95% confidence interval [95% CI] 0.51-0.86, P = 0.002). However, the absence of a cavesson increased the risk of lesions at the commissures of the lips 2.39 times compared with the loosest noseband (95% CI 1.4-4.11, P = 0.002). MAIN LIMITATIONS: The rules of the equestrian federation did not permit a full intraoral examination. Selection of rider/horse combination was not random. CONCLUSIONS: Lesions of the skin or mucosa at the commissures of the lips may be decreased by limiting noseband tightness and lesions on the chest wall may be decreased by limiting the length of spurs.

Forces and pressures beneath the saddle during mounting from the ground and from a raised mounting platform.

The objective was to use an electronic pressure mat to measure and compare forces and pressures of the saddle on a horse's back when riders mounted from the ground and with the aid of a mounting platform. Ten riders mounted a horse three times each from the ground and from a 35 cm high mounting platform in random order. Total force (summation of forces over all 256 sensors) was measured and compared at specific points on the force-time curve. Total force was usually highest as the rider's right leg was swinging upwards and was correlated with rider mass. When normalized to rider mass, total force and peak pressure were significantly higher when mounting from the ground than from a raised platform (P<0.05). The area of highest pressure was on the right side of the withers in 97% of mounting efforts, confirming the importance of the withers in stabilizing the saddle during mounting.

Short-term habituation of equine limb kinematics to tactile stimulation of the coronet.

UNLABELLED: A lightweight bracelet that provides tactile stimulation to the horse's pastern and coronet induces a higher flight arc of the hoof. This study addresses the pattern of habituation to these devices. OBJECTIVE: To evaluate short-term habituation to tactile stimulation of the pastern and coronet in trotting horses. METHODS: Tactile stimulation was provided by a lightweight (55 g) device consisting of a strap with seven chains that was attached loosely around the pastern. Reflective markers were fixed to the dorsal hoof wall, the forehead and over the tenth thoracic vertebra of eight sound horses. The horses trotted in hand 10 times at a consistent velocity along a 30 m runway under three conditions applied in random order at two-hour intervals: no stimulators, stimulators on both front hooves or stimulators on both hind hooves. One stride per trial was analyzed to determine peak hoof heights in the swing phase. Sequential trials with stimulators were compared with unstimulated trials using a nested ANCOVA and Bonferronni's post hoc test (P < 0.005). RESULTS: Peak hind hoof height increased significantly for all 10 trials when wearing hind stimulators, whereas peak fore hoof height increased during the first six trials only when wearing fore stimulators. The first trial with stimulators showed the greatest elevation, followed by a rapid decrease over the next three trials and then a more gradual decrease. CONCLUSIONS: If the goal is to facilitate a generalized muscular response, a short burst of tactile stimulation is likely to be most effective, whereas longer periods of stimulation will be more effective for strength training.

Comparison of mandibular motion in horses chewing hay and pellets.

REASONS FOR PERFORMING STUDY: Previous studies have suggested that temporomandibular joint (TMJ) kinematics depend on the type of food being masticated, but accurate measurements of TMJ motion in horses chewing different feeds have not been published. HYPOTHESIS: The temporomandibular joint has a larger range of motion when horses chew hay compared to pellets. METHODS: An optical motion capture system was used to track skin markers on the skull and mandible of 7 horses as they chewed hay and pellets. A virtual marker was created on the midline between the mandibles at the level of the 4th premolar teeth to represent the overall motion of the mandible relative to the skull during the chewing cycle. RESULTS: Frequency of the chewing cycles was lower for hay than for pellets. Excursions of the virtual mandibular marker were significantly larger in all 3 directions when chewing hay compared to pellets. The mean velocity of the virtual mandibular marker during the chewing cycle was the same when chewing the 2 feeds. CONCLUSIONS: The range of mediolateral displacement of the mandible was sufficient to give full occlusal contact of the upper and lower dental arcades when chewing hay but not when chewing pellets. POTENTIAL RELEVANCE: These findings support the suggestion that horses receiving a diet high in concentrate feeds may require more frequent dental prophylactic examinations and treatments to avoid the development of dental irregularities associated with smaller mandibular excursions during chewing.

3D kinematics of the equine metacarpophalangeal joint at walk and trot.

The metacarpophalangeal (MCP) joint and its supporting soft tissues are common sites of injury in athletic horses. Equine gait analysis has focused on 2D analysis in the sagittal plane and little information is available which describes 3D motions of the MCP joint and their possible role in the development of injuries. The aim was to characterize the 3D rotations of the equine MCP joint during walking and trotting. Three-dimensional trajectories of marker triads fixed rigidly to the third metacarpus and proximal phalanx of the right forelimb of healthy horses were recorded at walk (n = 4) and trot (n = 6) at 120 Hz using eight infra-red cameras. Kinematics of the MCP joint were calculated in terms of helical angles between the two segments using singular-value decomposition and spatial attitude methods. The ranges of motion were: flexion/extension: 62 +/- 7 degrees at walk, 77 +/- 5 degrees at trot; adduction/abduction: 13 +/- 7 degrees at walk, 18 +/- 7 degrees at trot; and axial rotation: 6 +/- 3 degrees at walk, 9 +/- 5 degrees at trot. Flexion/extension had a consistent pattern and amplitude in all horses and appeared to be coupled with adduction/abduction, such that stance phase extension was accompanied by abduction and swing phase flexion was accompanied by adduction. Axial rotation was small in amount and the direction varied between horses but was consistent within an individual for the two gaits.

3D kinematics of the interphalangeal joints in the forelimb of walking and trotting horses.

The objective was to measure 3D rotations of the distal (DIP) and proximal (PIP) interphalangeal joints at walk and trot. 3D trajectories of markers fixed to the proximal phalanx, middle phalanx and the hoof wall of the right forelimb of four sound horses were recorded at 120 Hz. Joint kinematics were calculated in terms of anatomically-based joint coordinate systems between the bone segments. Ranges of motion were similar at walk and trot. Values for the DIP joint were: flexion/extension: 46 +/- 3 degrees at walk, 47 +/- 4 degrees at trot; internal/external rotation: 5 +/- 1 degrees at walk, 6 +/- 3 degrees at trot; and adduction/abduction: 5 +/- 2 degrees at walk, 5 +/- 3 degrees at trot. Within each gait, kinematic profiles at the DIP joint were similar between horses with the exception of adduction/abduction during breakover, which may vary depending on the direction of hoof rotation over the toe. Knowledge of the types and amounts of motion at the DIP joint will be useful in understanding the aetiology and treatment of injuries to the soft tissues, which are being recognized more frequently through the use of sensitive imaging techniques. Ranges of motion for the PIP joint were: flexion/extension: 13 +/- 4 degrees at walk, 14 +/- 4 degrees at trot; adduction/abduction: 3 +/- 1 degrees at walk, 3 +/- 1 degrees at trot; and internal/external rotation: 3 +/- 1 degrees at walk, 4 +/- 1 degrees at trot. The PIP joint made a significant contribution to flexion/extension of the digit. During surgical arthrodesis, the angle of fusion may be important since loss of PIP joint extension in late stance is likely to be accommodated by increased extension of the DIP joint.

Ground reaction forces of elite dressage horses in collected trot and passage.

In this study, sagittal plane ground reaction forces (GRFs) in ridden elite dressage horses performing 'collected trot' and in 'passage' over ground were determined. In-ground force plates captured GRF data from four Dutch Warmblood and four Lusitano horses ridden by their trainers. At least three stance phases were analysed for forelimbs and hind limbs per horse. The variables extracted were vertical and longitudinal (braking, propulsive) force maxima, their times of occurrence and the respective impulses for forelimbs and hind limbs. Lusitanos had lower vertical impulses than Dutch Warmbloods in collected trot. Across all horses, passage had larger vertical impulses than collected trot in the forelimbs and hind limbs. Propulsive impulse increased in the hind limbs in passage. Prolonged stance durations in passage contributed to higher vertical impulses that are needed to increase the vertical excursions of the centre of mass.

A simple method for equine kinematic gait event detection.

BACKGROUND: Previous studies have validated methods for determining kinematic gait events using threshold-based techniques. However, a simple method that can be successfully applied to walk, trot and canter is yet to be identified. OBJECTIVES: To develop a simple kinematic method to identify the timing of hoof contact (hoof-on), peak vertical force and lift off (hoof-off), which can be applied in walk, trot and canter. STUDY DESIGN: In vivo method authentication study. METHODS: Horses (n = 3) were ridden in walk, trot and canter down a runway on which four force plates were arranged linearly. Three-dimensional forces were recorded at a sampling rate of 960 Hz and were synchronised with a 10-camera motion analysis system sampling at 120 Hz. Events identified from vertical ground reaction force (GRFz) data were hoof-on (GRFz>50N), peak vertical force (GRFzpeak ) and hoof-off (GRFz<50N). Kinematic identification of hoof-on and hoof-off events was based on sagittal planar angles of the fore- and hindlimbs. Peak metacarpophalangeal (MCP)/metatarsophalangeal (MTP) joint extension was used to assess the time of GRFzpeak . The accuracy (mean) and precision (s.d.) of time differences between kinetic and kinematic events were calculated for fore- and hindlimbs at each gait. RESULTS: Hoof-off was determined with better accuracy (range: -3.94 to 8.33 ms) and precision (range: 5.43-11.39 ms) than hoof-on across all gaits. Peak MCP angle (range: 5.83-19.65 ms) was a more precise representation of GRFzpeak than peak MTP angle (range: 11.49-67.75 ms). MAIN LIMITATIONS: The sample size was small and therefore further validation is required. The proposed method was tested on a single surface. CONCLUSIONS: This study proposes a simple kinematic method of detecting hoof-on, hoof-off and GRFzpeak at walk, trot and canter. Further work should focus on validating the methodology in a larger number of horses and should extend the method for use on surfaces with varying levels of compliance.

Effect of standing tarsal angle on joint kinematics and kinetics.

REASONS FOR PERFORMING STUDY: The tarsal joint is a frequent site of lameness, but little objective information is available regarding the effects of tarsal conformation on joint movements or forces. OBJECTIVE: To compare tarsal kinematics and kinetics in horses with large, intermediate and small tarsal angles. METHODS: Sagittal plane standing angle of the right tarsal joint was measured in 16 horses as they stood squarely with the hind hooves vertically beneath the hip joint. Tarsal angles were classified as small (< 155.5 degrees), intermediate (155.5-165.5 degrees) or large (> 165.5 degrees). Reflective markers, attached over the centres of joint rotation, were tracked during stance as the horses trotted across a force plate at a standardised speed. Joint angles and ground reaction forces were combined with morphometric data to calculate net joint moments and net joint powers across the tarsus using inverse dynamics. RESULTS: In all horses, the tarsus flexed during the impact phase and extended in late stance. Tarsal angles were stratified according to standing tarsal angle throughout stance. Horses with large standing angles showed less flexion and less energy absorption at the tarsus during the impact phase than those with intermediate or small angles and generated less vertical impulse than horses with small standing angles. Net extensor moment at the tarsus during stance was lower for horses with large standing angles. CONCLUSIONS: In horses with large tarsal angles, less concussion was absorbed during the impact phase, which may be a factor in the development of degenerative joint disease; and the smaller vertical impulse and extensor moment later in stance may limit propulsive ability. However, the smaller net joint moment may reduce the risk of plantar ligament desmitis. CLINICAL SIGNIFICANCE: The effects of conformation on kinematics and kinetics of the tarsal joint may influence both performance and soundness.

Stance phase kinematics and kinetics of horses trotting over poles.

REASON FOR PERFORMING STUDY: Trotting over poles is frequently used therapeutically to restore swing phase ranges of joint motion. It is not known whether ground reaction forces (GRFs) increase as the swing phase limbs are lifted higher to clear the poles. Higher GRFs might be painful or jeopardise healing of musculoskeletal injuries. OBJECTIVES: To measure stance phase kinematics and GRFs in the forelimbs and hindlimbs of horses trotting on level ground, over low poles and over high poles, and to test the hypothesis that trotting over poles is associated with increases in peak GRFs and impulses in the supporting hindlimb and forelimb compared with trotting over level ground. STUDY DESIGN: Repeated measures experimental study on horses with normal gait. METHODS: Kinematic and GRF data were collected from 8 horses trotting on level ground under 3 conditions performed in random order: no poles, low (11 cm) poles and high (20 cm) poles spaced 1.05 ± 0.05 m apart. Spatiotemporal and angular kinematic variables and GRFs were measured during stance. Comparisons among conditions were made using repeated measures ANOVA (P<0.05) with Bonferroni correction for post hoc testing. RESULTS: The only GRF component that increased when trotting over poles was peak forelimb braking GRF. Forelimb vertical and braking impulses increased and the transverse impulse changed from medially to laterally directed. Extension of the metatarsophalangeal and metacarpophalangeal joints did not change. CONCLUSIONS: The fact that peak vertical forces and extension of the metatarsophalangeal and metacarpophalangeal joints did not increase when trotting over poles suggests that loading of the musculoskeletal tissues is comparable with that associated with trotting on level ground in horses with symmetrical movement at trot. The findings support the use of trot poles during rehabilitation from lameness in horses that move symmetrically. The generation of laterally directed forelimb transverse forces suggests that trotting over poles may recruit the forelimb adductor musculature.

Swing phase kinematics of horses trotting over poles.

REASONS FOR PERFORMING STUDY: Trotting over poles is used therapeutically to restore full ranges of limb joint motion. The mechanics of trotting over poles have not yet been described, hence quantitative evidence for the presumed therapeutic effects is lacking. OBJECTIVES: To compare limb kinematics in horses trotting over level ground, over low poles and over high poles to determine changes in joint angulations and hoof flight arcs. STUDY DESIGN: Repeated measures experimental study in sound horses. METHODS: Standard motion analysis procedures with skin-fixed reflective markers were used to measure swing phase kinematics from 8 horses trotting on level ground, over low (11 cm) and high (20 cm) poles spaced 1.05 ± 0.05 m apart. Spatiotemporal variables and peak swing phase joint flexion angles were compared using repeated measures ANOVA (P<0.05) with Bonferroni correction for pairwise post hoc testing. RESULTS: Peak heights of the fore and hind hooves increased significantly and progressively from no poles (fore: 13.8 ± 3.8 cm; hind: 10.8 ± 2.4 cm) to low poles (fore: 30.9 ± 4.9 cm; hind: 24.9 ± 3.7 cm) and to high poles (fore: 41.0 ± 3.9 cm; hind: 32.7 ± 4.0 cm). All joints of the fore- and hindlimbs contributed to the increase in hoof height through increased swing phase flexion. The hooves cleared the poles due to increases in joint flexion rather than by raising the body higher during the suspension phases of the stride. CONCLUSIONS: The increases in swing phase joint flexions indicate that trotting over poles is effective for activating and strengthening the flexor musculature. Unlike the use of proprioceptive stimulation devices in which the effects decrease over time due to habituation, the horse is required to elevate the hooves to ensure clearance whenever poles are present. The need to raise the limbs sufficiently to clear the poles and place the hooves accurately requires visuomotor coordination, which may be useful in the rehabilitation of neurological cases. The Summary is available in Chinese - see Supporting information.

Development of conditioning programs for dressage horses based on time-motion analysis of competitions.

The time-motion characteristics of Canadian basic- and medium-level dressage competitions are described, and the results are applied in formulating sport-specific conditioning programs. One competition was analyzed at the six levels from basic 1 to medium 3. Each test was divided into a series of sequences based on the type and speed of activity. The durations of the sequences were measured from videotapes. The basic-level tests had fewer sequences, and they were shorter in distance and duration than the medium tests (P < 0.10), but the average speed did not differ between the two levels. It is recommended that horses competing at the basic levels be conditioned using 5-min exercise periods, with short (10-s) bursts of lengthened trot and canter included at basic 2 and above. In preparation for medium-level competitions, the duration of the work periods increases to 7 min, 10- to 12-s bursts of medium or extended trot and canter are included, and transitions are performed frequently to simulate the energy expenditure in overcoming inertia.

Natural infection with Dictyocaulus arnfieldi in pony and donkey foals.

From June to October 1978 four pony mares and foals and two donkey mares and foals grazed a paddock contaminated with Dictyocaulus arnfieldi larvae. No signs of respiratory disease were seen in the foals but within 11 weeks of exposure to the paddock all six developed patent lungworm infections. In October 1978 one donkey and two pony foals were killed. At post mortem examination parasites in various stages of development and measuring up to 8 cm in length were found in the lungs. At this time the three surviving foals were stabled for the remainder of the experiment. Two of these ceased passing D arnfieldi larvae during the winter months but in one pony foal patency persisted until the study ended in August 1979. Patent lungworm infections were not seen in the pony mares, although two started to cough four to six weeks after starting to graze the infected paddock. One of the affected mares was killed in October 1978 when seven small (less than 7 mm) D arnfieldi were recovered. The other continued to cough until the end of the study over a year later.

Experimental Parascaris equorum infection of foals.

Six worm-free pony foals, two to four months old, were infected with parascaris equorum eggs using three different dosage regimes and killed at either 40 or 95-100 days after infection. Coughing and a circulating eosinophilia were features of large infections from which only a small number of worms developed to maturity. In small infections a high percentage of the parasites matured in the small intestine and this was associated with unthriftiness. Pre-patent periods of 80 and 83 days were recorded.

The development of immunity to Parascaris equorum infection in the foal.

Following infection with 8000 Parascaris equorum eggs in two- to four-week-old foals reared under worm-free conditions a high percentage of the infective dose completed its tissue migration and returned to the small intestine. Patent infections were establisehd between 81 and 104 days after infection and high faecal egg counts were recorded. A group of six- to 12-month-old foals, which had been either reared under worm-free conditions or exposed to natural ascarid and strongyle infections on pasture, received a similar infection of 8000 P equorum eggs. Compared with the younger foals there was a marked reduction in the number of larvae reaching the small intestine. Also, patent infections were established less frequently (50 per cent of cases) and, when present, the faecal egg counts remained low.