bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of dietary phosphorus and calcium on induction of dyschondroplasia in foals
Authors: Savage C. J. , McCarthy R. N. , Jeffcott L. B.
Published: June 2010

Thirty mixed‐bred foals aged 2.5–6.5 months (mean age 4.4 ± 1.0 months,) with no clinical or radiographic lesions indicating dyschondroplasia (DCP) were each fed 1 of 4 diets for 16–18 weeks. Twelve foals were fed a Control diet according to NRC recommendations. Six foals were fed a diet ˜388% NRC recommended level for P; another 6 foals were fed a diet with ˜342% NRC level for Ca and the remaining 6 foals were fed a diet which contained both ˜342% NRC level for Ca and ˜129% NRC level for digestible energy (DE). Diets were formulated using different rice‐based pellets and oaten chaff, with added maize oil for the High DE diet, and additions of limestone (CaCO3) for the High Ca and sodium monophosphate (5.5% of the pellet) for the High P.

Foals fed excess DE (High Ca/DE group) had slightly greater average daily gains, humeral lengths and wither heights, but these were not significantly different from foals fed the Control diet. Clinical and radiographic signs of DCP were seen in 7 foals; 4 foals fed High P and 3 foals fed High Ca/DE. Suspicious joint lesions of DCP were identified atpost mortemin 13 foals (1 Control, 5 High P, 2 High Ca, 5 High Ca/DE). Histologically confirmed lesions of DCP were found in multiple joints and growth plates in 15 foals (2 Control, 5 High P, 2 High Ca, 6 High Ca/DE). The lesions were more numerous and severe in the foals fed High P and High Ca/DE than in the foals fed the Control and High Ca diets. High levels of dietary Ca did not appear to induce lesions of DCP in foals fed ˜100% NRC recommendation for dietary DE, or reduce the incidence in foals concurrently fed high dietary DE. High levels of P intake resulted in the formation of lesions in foals fed the basal level of DE (˜100% NRC DE), although the mechanism by which this occurred has not been elucidated.
Preliminary results of demineralised bone matrix implantation in horses
Authors: Douglas Janet , Clarke A. F.
Published: June 2010

In rats the subcutaneous or intramuscular implantation of allogeneic demineralised bone matrix (DBM) induces host mesenchymal cells to undergo endochondral ossification. In normal rats this process adheres to a rigid timetable, cartilage being present by Day 7 and bone by Day 12. This technique was applied to horses. Demineralised bone matrix from 3 different equine donors, a neonate, a yearling and a 4‐year old, was implanted intramuscularly or subcutaneously in 4 different equine hosts, aged 6 weeks to 6 years. Implants were removed 10–37 days later. No evidence of endochondral ossification was detected in any of the implants. As a control experiment, DBM prepared from rats was implanted into allogeneic hosts using the same bone preparation and implantation technique as was used in the horses. Endochondral ossification was induced in the rats, and the process followed the expected time course. Preliminary results suggest that hyaline cartilage formation does not occur in horses within 37 days. The present study does not exclude the possibility that endochondral ossification may occur in horses if longer implantation periods or different methods of DBM preparation are used.
Utilisation of an accelerometric device in equine gait analysis
Authors: BARREY E. , HERMELIN M. , VAUDELIN J. L. , POIREL D. , VALETTE J. P.
Published: June 2010

An accelerometric device was developed for evaluating the gait of young horses in field situations. Some measurements and data analysis were made to show its potential applications in gait analysis. The transducers consisted of two accelerometers measuring acceleration along the longitudinal and dorso‐ventral axes of the horses. They were put into a leather pocket applied over the sternum by means of an elastic girth fastened onto the horse. This accelerometric belt was connected to a light weight radio telemetric system. The signals were transmitted to a receiver connected to a portable microcomputer. An alternative method to use this device was to connect it directly to an analog‐digital converter of the microcomputer. The maximum data acquisition rate was 50 Hz for each accelerometer using the telemetric system and 3500 Hz using direct connection. The accelerometric device could be used either on a treadmill or in field situations. Longitudinal and dorsoventral acceleration of the sternum provided some information about basic temporal stride kinematics and kinetics of a running horse. Two tests illustrated the usefulness of the accelerometric belt to investigate the velocity‐dependent changes in stride frequency and longitudinal acceleration, and the gait asymmetry of a lame horse. Three signal analysis procedures were used for data analysis, respectively: Fourier analysis, peak‐finding and autocorrelation functions. It was concluded that the accelerometric belt allows an objective study of some basic characteristics of the horse locomotion in field situations. It could be useful to test young horses provided that standardised protocols are developed to measure and analyse the acceleration data.
Surface strain on the dorsomedial metacarpus of yearling Thoroughbreds at different speeds and gaits on a treadmill
Authors: DAVIES H. M. S. , McCARTHY R. N.
Published: June 2010

Stacked rectangular rosette strain gauges were used to measure surface bone strain on the dorsomedial cortex of the third metacarpal bones in 6 yearling (16 to 19 months old) Thoroughbred horses during exercise on a treadmill. The peak principal compressive and tensile strains, angle of the peak strains and strain rate during loading were calculated and compared with speed and gait. At speeds ranging from 4 to 16.5 m/s there was compression of the dorsomedial cortex of the metacarpus and the magnitude of compression and rate of compression were proportional to the speed of exercise. At the walk (2 m/s) tension was recorded in some strides. The mean maximum compressive strains in the 6 horses were −966 μstrain at 2 m/s; −1630 μstrain at 4 m/s; −2172 μstrain at 6 m/s; −2857 μstrain at 8 m/s; −3500 μstrain at 10 m/s; and −3911 μstrain at 12 m/s. Recordings from 3 horses gave a mean −5028 μstrain at 14 m/s. One horse gave a mean −6296 μstrain at 16.5 m/s. These strains were all about 25% higher than those recorded from the metacarpus of adult Thoroughbreds under similar exercise conditions. It was concluded that the higher strains may predispose the young Thoroughbred racehorse to dorsal metacarpal disease.
Coordination of equine forelimb motion during the gallop
Authors: DEUEL NANCY R.
Published: June 2010

The objective of this study was to compare shoulder, elbow and carpus rotations bilaterally during the gallop in an investigation of intralimb coordination of the foreleg during high‐speed asymmetrical quadrupedal locomotion. The motion patterns of the forelimb during the gallop stride were documented using high‐speed cinematography. The gallop stride characteristics of 4 Quarter Horse fillies, approximately 30 months of age, were examined. Horses were housed and fed together and received the same amount and type of limited training, and were all ridden with the same tack by one person. Both sides of each horse were filmed simultaneously (243 frames/s) while galloping individually along a 1.5 m‐wide track. Kinematic variables describing 29 strides (16 left lead, 13 right lead; mean velocity 13.1 m/s, stride frequency 2.60 strides/s, stride length 5.06 m) included temporal and linear measurements of the approximate centres of rotation of the shoulder, elbow and carpal joints; maximum and minimum relative angles and angular velocities of those joints; and maximum and minimum angles with respect to the horizon of the scapula, humerus, radius and metacarpus segments. In both forelimbs, hoof impact was followed sequentially by maximal carpal extension and maximal elbow extension in weightbearing during the stance phase. Hoof lift‐off was followed sequentially by maximal carpal flexion, maximal shoulder flexion, maximal elbow flexion and simultaneous shoulder maximal extension and an initial extension peak of carpus well prior to hoof impact. Temporal patterns of forelimb motion at the gallop appear to originate proximal to the elbow joint. Distal to the shoulder joint, basic motion patterns are remarkably similar on the leading and trailing sides of the body. A high degree of reciprocity in shoulder joint action was observed, a mechanism contributing to the energetic economy of the equine gallop.
Drop hammer tests of Scandinavian harness racetracks
Authors: DREVEMO S. , HJERTÉN G. , JOHNSTON C.
Published: June 2010

Drop tests were carried out on 8 Scandinavian harness racetracks in order to evaluate their shock force attenuation properties. A drop hammer model was designed to simulate the hoof strike of the horse. The analysis comprised calculations for mean hardness index, impact time and energy loss which were correlated to ground composition parameters. The range of hardness, impact time and energy loss was 246–366 s−1, 7.6–13.2 ms and 74–95%, respectively at the inner lane of the track when the fallheight 0.6 m was used. The corresponding data for an outer lane were 225–392 s−1, 8.2–13.4 ms and 78–93%. The study showed significant differences in hardness, impact time and energy absorption between racetracks and between different test areas along the same course, with the outer lane usually being the harder. The drop height 1.5 m simulated a higher hoof landing velocity but gave similar results.

It is suggested that impact force influence from the ground may be detrimental to horses and significant effort should be made in track construction and management. It is postulated that tracks with adequate cushioning are likely to prevent excessive shock loading and related musculo‐skeletal disorders in racehorses.
Biokinematic differences between riding horses judged as good and poor at the trot
Authors: HOLMSTRÖM M. , FREDRICSON I. , DREVEMO S.
Published: June 2010

The trotting gait of 4 approved Swedish Warmblood stallions with a mean gait score ≥8.67 (maximum score = 10) at official performance tests and 4 horses with poor gaits (mean gait score ≤6.5) was recorded by high speed film (250 frames/s). Angular patterns and hoof trajectories of the left fore and hind limbs were analysed and presented as mean and standard deviation curves. The good horses had longer stride duration (p<0.001) and larger positive diagonal advanced placement (p<0.01). The swing phase retraction in the forelimbs was longer in the good horses. The most important differences in the forelimb angular patterns were found in the elbow and carpal joint angles. They were considerably more flexed in the good horses at the beginning of the swing phase retraction. Larger decrease of the pelvis inclination, increase of the femur inclination and larger flexion of the hock and hind fetlock joints during the stance phase were correlated with high trot scores. This indicates that storage of elastic strain energy during the stance phase may be important for the elasticity, energy and propulsion in trot.
Stress and strain of equine tendons of the forelimb at failure
Authors: JANSEN MARGOT O. , SAVELBERG H. H. C. M.
Published: June 2010

Tendons of 12 equine forelimbs were loaded until failure using a drawbench. Preceding the tensile test, the cross sectional area was measured at the narrowest site of the tendon. Small beads were sutured to the tendons, as markers for length change measurement from photographs. During loading, photographs were taken at about 3 Hz and the load was recorded. The maximal strain was calculated by means of linear regression of length‐time data and extrapolation to the instant of failure according to the force‐time curve. Total failure of the superficial and deep digital flexor tendons, the distal check ligament and the suspensory ligament occurred at a strain (± sd) of respectively 10.9 (± 1.4), 9.5 (± 1.5), 12.4 (± 1.0) and 11.6 (± 1.4) % and at a stress of respectively 116 (± 21), 133 (± 14), 86 (± 11) and 70 (± 12)MPa.
Relationships between ground reaction force patterns and kinematics in the walking and trotting horse
Authors: MERKENS H. W. , SCHAMHARDT H. C.
Published: June 2010

Simultaneous recordings were made of retardatory‐propulsory horizontal (Fy) and vertical (Fz) ground reaction forces (GRF), and kinematics of the fetlock joint and the hoof‐sole with respect to the ground of the right forelimbs and hind limbs of 4 Dutch Warmbloods, at the walk and the trot. The impact oscillation visible in Fy and Fz is the same at the walk and trot, and differs between fore‐ and hind limbs. The angulation pattern of the fetlock joint does not follow the faster oscillations visible in the GRF. The change in the course of Fy and Fz in the final stage of ground contact is caused by onset of heel lift‐off.
Objective determination of ground contact of equine limbs at the walk and trot: comparison between ground reaction forces, accelerometer data and kinematics
Authors: SCHAMHARDT H. C. , MERKENS H. W.
Published: June 2010

Mutual timing relationships between hoof and fetlock joint kinematics, and objective criteria for ground contact based on accelerometry and ground reaction force measurements, were obtained for the right forelimbs and hind limbs of 4 horses at the walk and trot. Initial ground contact can be determined from accelerometer data or force plate signals, but not with sufficient accuracy from kinematics only. Prior to initial ground contact the hoof is positioned with the heels lowered in 3 of 4 horses. The change to foot flat occurs within 9 ms and can be identified unequivocally, provided that the hoof is visible and the recording equipment is sufficiently fast. Assuming that the onset of the stance phase is known, the end of the stance phase can be determined within 10% stride duration from the time at which the fetlock joint angle is identical to that at initial ground contact. Another criterion is the time at which the metacarpus or metatarsus and the first phalanx are aligned.
Review Article: Echocardiography
Authors: BONAGURA J. D. , BLISSITT KAREN J.
Published: June 2010

Echocardiography encompasses a number of specific imaging techniques. The two‐dimensional (2‐D) echocardiogram is used to identify lesions of the heart and great vessels, assess myocardial function and provide a template for guiding contrast echocardiography, colour‐coded Doppler echocardiography and spectral Doppler studies. M‐mode echocardiography is used to measure cardiac size and ventricular function and can be combined with contrast or colour‐coded Doppler studies for accurate timing of flow events. Pulsed wave and continuous wave Doppler echocardiography display the direction and velocity of red blood cells within the heart and circulation. Continuous wave Doppler studies are used to calculate pressure gradients in the circulation. Any of the Doppler techniques can be used to identify abnormal or high velocity flow responsible for pathologic heart murmurs. Each Doppler format is complementary to the others: colour‐coded Doppler is used to screen large areas for flow disturbances; pulsed wave Doppler can pinpoint regions of abnormal flow; and continuous wave Doppler quantifies the maximal velocities of blood flow across cardiac lesions. Echocardiographic studies are very useful for the diagnosis and assessment of horses with cardiac murmurs, arrhythmias, and poor exercise performance. A number of cardiac disorders can be evaluated by echocardiography, including: cardiac malformation, valvular heart disease, cardiomyopathy, bacterial endocarditis, pericardial effusion, and congestive heart failure. When combined with a careful clinical examination, exercise evaluation and results of electrocardiography, the echocardiogram provides the best overall clinical assessment of the equine heart.
Echocardiographic measurements of cardiac dimensions and indices of cardiac function in normal adult Thoroughbred horses
Authors: PATTESON M. W. , GIBBS CHRISTINE , WOTTON P. R. , CRIPPS P. J.
Published: June 2010

Cardiac dimensions and indices of cardiac function were measured in 29 clinically normal adult Thoroughbreds (TB) which performed minimal exercise using guided M‐mode and two‐dimensional (2‐D) echocardiography, from a variety of image planes and measurement methods, and standardised imaging planes based on intracardiac anatomical landmarks. The different methods of measuring these variables were compared. The variables which were considered to be most valuable for quantitative echocardiography were measured in a further 9 horses.

Comparable measurements of cardiac dimensions can be obtained from a variety of different imaging planes, using either 2‐D or guided M‐mode echocardiography from the left or right side of the chest, although differences in measurement methods must be taken into account. The results of this study give a useful range of dimensions and indices of cardiac function in normal adult TBs for comparison with those recorded from horses with suspected cardiac disease. Comparisons are only valid if there is meticulous attention to correct orientation of imaging planes with regard to internal landmarks and that comparable measurement locations and timing are used.
Echocardiographic measurements of cardiac dimensions in normal ponies and horses
Authors: SLATER J. D. , HERRTAGE M. E.
Published: June 2010

Echocardiographic examinations were performed on 41 clinically normal small ponies, large ponies and horses. Using standardised two‐dimensional (2‐D) echocardiographic images to guide M‐mode studies, the interventricular septal thickness, left ventricular internal dimension and left ventricular wall in systole and diastole, and aortic diameter in diastole were measured. Normal values for these echocardiographic dimensions were obtained across a wide range of bodyweights. Although there was a trend for echocardiographic dimensions to increase with bodyweight across the whole range of animals examined, little or no linear correlation was found between dimensions and bodyweight within the small pony, large pony and horse groups.
Effects of sedation with detomidine hydrochloride on echocardiographic measurements of cardiac dimensions and indices of cardiac function in horses
Authors: PATTESON M. W. , GIBBS CHRISTINE , WOTTON P. R. , CRIPPS P. J.
Published: June 2010

Twenty‐six horses were sedated with detomidine hydrochloride (Domosedan, SmithKline Beecham Animal Health, Tadworth, Surrey, UK) at a dose of 10 μg/kg bwt, administered i.v. Echocardiograms were recorded before and after sedation, measurements of cardiac dimensions were made and functional indices were calculated. The pre‐ and post sedation values were compared. No significant change was detected following sedation in the ejection time (ET), left ventricular dimension, left atrial diameter at the sinotubular junction at end‐systole or end‐diastole or at the sinus of Valsalva at end‐diastole. Sedation was found to result in a statistically significant increase in end‐systolic left ventricular diameter and internal area and aortic diameter measured at the sinus of Valsalva. Left ventricular free‐wall thickness and interventricular septal thickness at end‐systole, fractional shortening, fractional area change and heart rate were significantly reduced following sedation. A significant increase in pre‐ejection period (PEP), duration of electromechanical systole (EMS) and PEP/ET (ejection time) was detected.
Colour flow Doppler echocardiography in normal horses
Authors: BLISSITT KAREN J. , BONAGURA J. D.
Published: June 2010

Colour flow Doppler echocardiography is a technique that is used with two‐dimensional (2‐D) echocardiography to study blood flow patterns in the heart and blood vessels. This method was used to define normal flow patterns and to evaluate valvular function in 40 clinically normal Thoroughbred and Thoroughbred cross horses. Flow patterns from 10 standardised echocardiographic images were described in relation to anatomic landmarks and timing during the cardiac cycle. Consistent intracardiac flow patterns were identified in the normal horses. High velocity flow signals or regurgitant jets were recorded at the tricuspid (77.5%), mitral (67.5%), aortic (47.5%) and pulmonary valves (40%) in clinically normal horses. Most of these signals were transient, and many were associated with valve closure.

This study demonstrates that colour flow Doppler echocardiography is a sensitive technique for the detection of intracardiac flow in horses. It will provide a basis by which to compare studies in horses suspected of having valvular heart disease.
Feasibility of transoesophageal echocardiography for evaluation of left ventricular performance in anaesthetised horses
Authors: YOUNG LESLEY E. , BLISSITT KAREN J. , CLUTTON R. E. , MOLONY V. , DARKE P. G. G.
Published: June 2010

Transoesophageal Doppler echocardiography was performed in 7 Thoroughbred horses anaesthetised with halothane. The procedure was performed on 4 occasions under standard conditions. On one occasion dobutamine hydrochloride was infused at 4 μg/kg/min for 20 min. Recordings of aortic blood velocity, obtained using high pulsed repetition frequency Doppler echocardiography (HPRF), were used to derive maximum acceleration (dv/dtmax), maximum velocity (Vmax), left ventricular ejection time (ET), pre‐ejection period (PEP), velocity time integral (VTI) and cardiac output (CO).

The coefficient of variation and 95% confidence intervals were narrower for the Doppler variables than for those obtained from cardiac catheterisation. For each horse the anaesthetic to anaesthetic repeatability of the Doppler indices of left ventricular function, exceeded that of maximum rate of rise of left ventricular pressure (LVdp/dtmax). The horse to horse variability was significant for heart rates Vmax, dv/dtmax, and VTI. After dobutamine infusion there were significant changes in all measured variables except heart rate, VTI and CO. The % change that occurred exceeded the predicted 95% confidence intervals for single measurements in all significantly affected variables. This suggests Doppler indices of cardiac performance may be useful to assess changes in haemodynamic function.

Passage of the probe into the oesophagus was not associated with serious adverse effects. Mild serous nasal discharge was visible for up to 24 h after the horses recovered from anaesthesia. Mild nasal haemorrhage occurred on 5 occasions during probe insertion. It is concluded that transoesophageal Doppler echocardiography provides a minimally invasive, continuous method for monitoring left ventricular systolic performance in anaesthetised horses.
Review Article: Heart murmurs in horses: determining their significance with echocardiography
Authors: REEF VIRGINIA B.
Published: June 2010

Physiological flow murmurs occur frequently in horses and may be difficult to distinguish from murmurs associated with underlying cardiac disease. The significance of heart murmurs auscultated in horses is often difficult to determine if the horse is not exhibiting any clinical signs or if the signs, such as poor performance, are nonspecific. A complete echocardiographic examination (M‐mode, 2‐dimensional (2‐D) and Doppler) provides an objective assessment of the severity of the horse's underlying cardiac disease. Valvular regurgitation and ventricular septal defects (VSDs) occur frequently and may impair performance, result in the horse's premature demise or have no apparent effect on the horse's life expectancy or performance capabilities. The echocardiographic findings that are used to formulate a prognosis for longevity and performance in horses with valvular regurgitation include the abnormalities detected on the valve leaflets, degree of cardiac chamber enlargement, severity of the resultant volume overload, size of the regurgitant jet, and relative relationship of jet size to chamber size. The echocardiographic findings that are used to formulate a prognosis for horses with VSDs are the number, size and location of the defect(s), degree of left ventricular volume overload, maximal velocity and direction of shunt flow through the defect and the presence and severity of concurrent valvulus regurgitation. Knowledge of the natural progression of the common types of cardiovascular disease in horses, coupled with the echocardiographic findings, clinical history and owner's or trainer's expectations can help the veterinarian form en accurate prognosis for life and performance in horses with heart murmurs.
Colour flow Doppler echocardiography in horses with cardiac murmurs
Authors: BLISSITT KAREN J. , BONAGURA J. D.
Published: June 2010

Thirty‐two horses with cardiac murmurs typical of tricuspid, mitral and aortic regurgitation were studied using colour flow Doppler echocardiography. The dimensions and duration of any regurgitant signals, recorded at the cardiac valve suspected as being the site of origin of the murmur, were measured. Results were compared with flow signals described at the valves of normal horses (Blissitt and Bonagura 1995). Horses with murmurs suggestive of tricuspid (n=8) and aortic (n=8) regurgitation showed larger regurgitant signals at the tricuspid and aortic valves respectively, than has been reported in normal horses. Horses with murmurs suggestive of mitral regurgitation (n=8) had a regurgitant signal of longer duration than occurs in normal horses, but the jets were not larger. Comparison of two groups of horses with low and high grade murmurs of tricuspid regurgitation, showed that horses with louder murmurs had significantly longer jets of larger area than those with low grade murmurs. This study demonstrates that colour flow Doppler echocardiography is a sensitive technique for the detection of valvular regurgitation in horses. However, quantification of jet size and duration are important for distinguishing physiological backflow which occurs in normal horses (Blissitt and Bonagura 1995) from valvular regurgitation associated with cardiac murmurs.
Characterisation of beta‐adrenoceptors in equine digital veins: implications of the modes of vasodilatory action of isoxsuprine
Authors: ELLIOTT J. , SOYDAN J.
Published: June 2010

Isolated equine digital veins (EDVs) were used to study β‐adrenoceptor mediated vasodilation and to examine isoxsuprine's vasodilatory mechanism of action. When the blood vessel wall tension was raised with potassium chloride solution (KCl; 59 mmol/l), the order of vasodilator potency of β‐agonists was: isoprenaline > fenoterol > noradrenaline > dobutamine > isoxsuprine. The β2‐selective adrenoceptor antagonist, ICI 118551 (1 nmol/1) caused a 6.74 and 6.65‐fold parallel shift to the right in the dose response curves to fenoterol and noradrenaline respectively. Propranolol (10 nmol/l) inhibited the vasodilatory action of isoprenaline in a competitive manner (19.6 ± 6.4‐fold parallel shift to the right) but was much less effective as an inhibitor of isoxsuprine's vasodilatory action. Isoprenaline and fenoterol were just as effective as vasodilators when blood vessel wall tension was raised with KCl, the thromboxanemimetic U44069 (9, 11‐dideoxy‐9α, 11α‐epoxymethano‐prostaglandin F2α; 30 nmol/l) or the α1‐adrenoceptor agonist, phenylephrine (0.3 μmol/l). In addition, fenoterol's relaxation of U44069‐induced tone was competitively inhibited by the β2‐selective adrenoceptor antagonist ICI 118551 (8.4 ± 0.9‐fold parallel shift to the right). By contrast, isoxsuprine was 81.9 times more potent as a vasorelaxant of phenylephrine‐induced tone when compared with KCl‐induced tone and proved completely ineffective as a vasodilator of U44069‐induced tone. When dose response curves to α‐adrenoceptor vasoconstrictor agonists were obtained in the presence of isoxsuprine (0.1 μmol/l), competitive antagonism occurred with methoxamine and noncompetitive antagonism with BHT‐920. These data suggest EDVs possess β2‐adrenoceptors mediating vasodilation. Isoxsuprine is an α1‐selective adrenoceptor antagonist but has very low potency and efficacy as a β‐adrenoceptor agonist in this functional bioassay. Indeed, much of the vasodilatory action of isoxsuprine may be due to a mechanism which does not involve β‐adrenoceptors.
Quinidine administration increases steady state serum digoxin concentration in horses
Authors: PARRAGA MARIA E. , KITTLESON M. D. , DRAKE CHRISTIANA M.
Published: June 2010

The aim of this study was to determine if quinidine administration increases steady state serum digoxin concentration in horses. Digoxin (0.01 mg/kg q. 12 hper os) was administered to 6 horses for 7 days. Steady state was confirmed by identifying statistically indistinguishable peak and trough serum digoxin concentrations on Days 4, 5, and 6. On Day 6, serum digoxin concentration was measured at baseline and 0.25, 0.5, 1, 2, 4, 6, 8 and 12 h after digoxin administration. On Day 7, quinidine (20 g at baseline and 10 g at 2, 4 and 6 h) was administeredper osand serum digoxin concentration was measured at the same time intervals. Creatinine and renal digoxin clearances were measured on Days 6 and 7. Results indicated that there was approximately a doubling of serum digoxin concentration (from mean ± s.d. 2.57 ± 0.96 ng/ml at baseline to 4.28 ± 1.31 at 15 min and 5.98 ± 1.21 ng/ml at 30 min) after starting the administration of quinidine.

This elevation persisted for the 12 h after starting quinidine administration. Renal digoxin and endogenous creatinine clearances decreased but the decrease in digoxin clearance was greater. Serum quinidine concentration achieved the therapeutic range (2–6 μg/ml) in 5 of the 6 horses. In summary, similar to findings in other species, quinidine administration increases steady state serum digoxin concentration in horses and this occurs, at least in part, due to a decrease in renal digoxin clearance. Some of the decrease in renal clearance is due to decreased glomerular filtration which is dissimilar to findings in other species.
Preparing for and competing in the heat: the human perspective
Authors: MAUGHAN R. J. , LINDINGER M. I.
Published: June 2010

This review provides an overview of the challenges that face man and horses when exercising in the heat. Some of the strategies that are used and are being developed for human atheletes exercising in the heat are reviewed. There are many similarities between human and equine physiological responses to exercise in the heat; and equine exercise science may gain some useful insights from the training, fluid replacement and heat acclimatisation strategies used by human athletes. There are, however, some important differences that impact on the ability of horses to thermoregulate and to regulate fluid and electrolyte balance. The major differences are the low surface area to body mass ratio in horses compared to man; and the high metabolic capacity of equine skeletal muscle. These 2 factors may limit the ability of horses to dissipate heat when exercise is performed under hot conditions. Some of the more important equine differences are highlighted within the context of the ‘human perspective’.
Electrolyte and total protein changes in nonheat acclimated horses performing treadmill exercise in cool (20°C/40% RH), hot, dry (30°C/40% RH) or hot, humid (30°C/80% RH) conditions
Authors: HARRIS PATRICIA A. , MARLIN D. J. , SCOTT C. M. , HARRIS R. C. , MILLS P. C. , MICHELL A. R. , ORME C. E. , ROBERTS C. A. , SCHROTER R. C. , MARR CELIA M. , BARRELET F.
Published: June 2010

Four horses (H, J, N and M) undertook a simulated competition exercise test (CET), designed to simulate physiological and metabolic stresses of the Speed and Endurance (S & E) test of a 3‐day‐event, under 3 different environmental conditions: 20°C/40% relative humidity (RH) (cool, dry [CD] 2 sessions); 30°C/40%RH (hot, dry [HD]) and 30°C/80%RH (hot, humid [HH]) (Marlinet al.1995a). Venous blood samples for electrolyte and total protein (TP) determinations were collected from indwelling catheters at predetermined time points throughout each CET and initial 30 min recovery period. Venous blood samples were collected by jugular venepuncture at 2 h and 24 h after the end of the final 8 min canter (Phase D). The effects of exercise, environmental condition and horse on venous TP, sodium (Na+), potassium (K+), chloride (Cl−), calcium (Ca2+), magnesium (Mg2+) and phosphate (PP43‐) plasma concentrations were investigated. In addition, the effect of environmental condition on estimated cation loss was evaluated.

All horses completed the full CET under the CD and HD conditions, but only one horse completed the full 8 min of the final canterPhase Dunder HH conditions. Exercise had a significant (P<0.05) effect on all parameters similar to those reported previously in field competitions. There was a significant (P<0.05) interaction between time and horse for TP, Na+and Cl−. Overall, the environmental condition had a significant (P<0.05) effect on all parameters, but the differences were not considered to be of any physiological relevance, other than for Cl−and TP. There was a significant (P<0.05) interaction between time and environmental condition for Cl−and TP only. During much of the CET and recovery period, mean Cl−values were higher with the first CD session than the second CD session or under the HH or HD conditions. For TP after 2 min ofPhase Dand during the initial recovery period, concentrations were higher under the HH conditions and returned to the Pre‐ values less quickly. There were marked individual variations in the estimated cation losses and no consistent effect of environmental condition was found. Although estimated fluid loss was similar following both HD and HH sessions, restoration of bodyweight was slower following the CET studies under HH conditions.
Physiological responses of horses competing at a modified 1 Star 3‐day‐event
Authors: KOHN CATHERINE W. , HINCHCLIFF K. W. , McCUTCHEON L. J. , GEOR R. , FOREMAN J. , ALLEN A. K. , WHITE SUSAN L. , MAYKUTH PATRICIA L. , WILLIAMSON LISA H.
Published: June 2010

The impending 1996 summer Olympic 3‐day‐event in Atlanta has focused attention on the need to determine what modifications to the demanding Endurance Test will be required to ensure safety of the horses competing. Three groups of horses participated in a Field Trial held in August of 1994 in northern Georgia to determine the safety and feasibility of conducting a modified 3‐day‐event in hot, humid weather. One group (TD) completed a modified 1 Star 3‐day‐event test, a control group (HT) completed a Horse Trial identical to the modified 1 Star test except for the omission ofPhases BandCand the third group (E), comprised of European horses, completed the modified 1 Star test with a longer, fasterPhase Cthan was used for TD.

During the Endurance Test, the ambient temperature and relative humidity ranged from 24.3°C and 98.9% in the morning to 30.2°C and 51.6% in the afternoon. No horse failed to complete the Trial because of heat stress or fatigue. There were no significant (P<0.05) differences detected in heart rate, rectal temperature, respiratory rate or net weight loss between HT and TD horses at any observation time. The highest rectal temperature recorded at the end ofPhase Cwas 39.6°C. These findings suggest that the modified 1 Star Endurance Test was as well tolerated by American horses as the control Horse Trial test. Rectal temperature was significantly higher for E than for TD or HT at the finish ofPhase C.European horses had significantly greater decreases in weight than HT and TD at the end ofPhases CandDand the next day. These findings probably reflect the faster and longer work effort of E horses duringPhase C.

Modification ofPhase Cand the rest‐pause to ensure that recovery and heat dissipation occurred before the start ofPhase Dresulted in a 3‐day‐event that was safe for horses. The Field Trial provides a model for designing a modified Olympic Endurance Test. If the 1996 Olympic 3‐day‐event is held in hotter and more humid weather than the Field Trial, additional modifications to the Endurance Test (decreased distances, speeds and numbers of jumping efforts) will probably be required to ensure safety of competing horses.
Acid:base and serum biochemistry changes in horses competing at a modified 1 Star 3‐day‐event
Authors: HINCHCLIFF K. W. , KOHN CATHERINE W. , GEOR R. , McCUTCHEON L. J. , FOREMAN J. , ANDREWS F. M. , ALLEN A. K. , WHITE SUSAN L. , WILLIAMSON LISA H. , MAYKUTH PATRICIA L.
Published: June 2010

We examined the effects of participation in each of 3 modifications of Day 2 of a 3‐day‐event on blood and serum variables indicative of hydration, acid:base status and electrolyte homeostasis of horses. Three groups of horses − 8 European (E) horses and 2 groups each of 9 North American horses performed identical Days 1 (dressage) and 3 (stadium jumping) of a 3‐day‐event. E horses and one group of the North American horses (TD) performed modifications of Day 2 of a 1 Star 3‐day‐event and the other group of North American horses (HT) performed a Horse Trial on Day 2. Jugular venous blood was collected from each horse on the morning of Day 2 before any warm‐up activity, between 4 min 55 s and 5 min 15 s afterPhase Dand the following morning. Eight E horses, 5 TD horses and 8 HT horses completed the trials. There were few significant differences in acid:base or serum biochemistry variables detected among horses performing either 2 variations of the Speed and Endurance day of a 1 Star 3‐day‐event, or a conventional Horse Trial. Failure to detect differences among groups may have been related to the low statistical power associated with the small number of horses, especially in the TD group, variation in quality of horses among groups and the different times of the day at which the E horses competed. Differences detected among time points were usually common to all groups and demonstrated metabolic acidosis with a compensatory respiratory alkalosis, a reduction in total body water and cation content, and hypocalcaemia. Importantly, horses of all groups did not replenish cation, chloride, and calcium deficits after 14–18 h of recovery.
Water and ion losses during the cross‐country phase of eventing
Authors: ECKER GAYLE L. , LINDINGER M. I.
Published: June 2010

Loss of total body water and ions during prolonged exercise can predispose the horse to health and performance problems. This study examined total body water (TBW) losses and extracellular (ECF) ion losses during the crosscountry (XC) phase of Preliminary, Intermediate and Advanced Horse Trials and CCI level 3‐day‐events. Jugular venous blood samples and body mass (BM) were collected on 49 horses at rest, Pre‐XC, Post‐XC and following 30 min of recovery. Plasma was separated from blood cells within 10 min of collection. Plasma was analysed for [Na+], [K+], [Cl−], ionised [Ca++], [glucose], [lactate] and packed cell volume (PCV) and plasma [protein] ([PP]). Distances ranged from 3000–6000 m for the XC phase with speeds of 500–570 m/min. In general, losses of TBW, Na+and Cl−increased with increasing level of difficulty. Loss of TBW Post‐XC ranged from 2–6.1% of resting values or 8.9–12.6 litres for the Preliminary level to mean ± s.e. 20.4 ± 1.8 litres for CCI. Losses of ECF ions ranged from 0.5–6.4% for Na+, 1.2–7.7% for Cl−, gains of 8% to losses of 23% for K+, and gains of 7% to losses of 11.7% for Ca++at 30 min Post‐XC. There was little recovery following 30 min and deficits of 5.3 ± 2.5 litres persisted overnight in horses that were tested. Plasma protein and PCV increased Post‐XC and PCV remained elevated above resting values at 30 min recovery. It is concluded that significant water and ion losses occur and, in general, increase with increased level of difficulty. There was little change with 30 min of recovery and for some horses losses persisted overnight.
Physiological measurements in horses after strenuous exercise in hot, humid conditions
Authors: ART TATIANA , VOTION DOMINIQUE , LEKEUX R.
Published: June 2010

The purpose of this study was 1) to measure and compare some physiological parameters in horses during a standardised treadmill exercise performed either in temperate atmospheric conditions (TC) (ambient temperature: 15°C; relative humidity: 55%), or in hot and humid conditions (HHC) (ambient temperature: 30°C; relative humidity: 75%) and 2) to follow the recovery of the same horses during 1 h after both tests. Five healthy fit Standardbred horses were investigated twice at 8 days interval, in TC and in HHC. Some measurements were made during a standardised treadmill exercise test (SET), others during a 1 h recovery period. The SET consisted of 8 min warm‐up and 8 min exercise.

During the SET, respiratory airflow and O2and CO2fraction in the respiratory gases were continuously recorded, using 2 ultrasonic pneumotachographs connected to a face mask and a mass spectrometer. Oxygen uptake (V̇O2), carbon dioxide output, respiratory quotient and expired minute volume (V̇E) were obtained on a breath‐by‐breath basis. The maximal values obtained during the highest intensity of the SET and the values obtained 2 min after the end of the test were used for the comparison between both tests. Heart rate (HR) and skin temperature were continuously recorded, using a heart rate recording system and a real time infrared thermographic unit, respectively. After both SETs in TC and HHC, the horses recovered in TC. Heart rate, respiratory frequency (f) and rectal temperature were regularly measured during 1 h after the test. Venous blood was sampled after the completion of the test for biochemical analysis, namely plasma electrolytes and enzymatic activities.

Exercising in HHC induced a reduction of the aerobic metabolism to the total energy requirement, i.e. a 20% decrease of V̇O2and 55% increase in lactate, as well as a decrease in V̇E. The increase in rectal and skin temperature, the dehydration and the weight loss were higher in HHC than in TC. During the recovery period the HR and f remained higher up to 30 min after the end of the SET in HHC while the rectal temperature remained higher up to 60 min after the end of this test. Therefore, despite the fact that our horses recovered in TC after exercising in HHC, there were significant differences between their physiological parameters measured during the recovery. This means that the recovery in air‐conditioned unit would probably be an insufficient measure to ensure an adequate cooling of the horses and justify consequently the adaptations proposed by the Federation Equestre Internationale (FEI), i.e. the decrease of the distance of the run and the increase of the time devoted to the halt between phases.
The effects of tonicity, glucose concentration and temperature of an oral rehydration solution on its absorption and elimination
Authors: LEÓN L. A. SOSA , DAVIE A. J. , HODGSON D. R. , ROSE R. J.
Published: June 2010

Effects of different tonicities, glucose concentrations and temperatures of an oral rehydration solution (ORS) on its uptake and elimination in resting horses were studied. Fluid and electrolyte deficits similar to those occurring during prolonged exercise were induced by the administration of 1 mg/kg bwt of frusemide i.m., 3 h prior to the ORS. Fluid was administered via nasogastric tube at a volume equivalent to 4% bodyweight, which approximated diuretic induced losses. The uptake of fluid was evaluated by changes in haematocrit (PCV) and plasma total protein concentration (TP). Changes in electrolyte balance were studied by measurements of plasma and urinary electrolyte concentrations while changes in bodyweight, urine volume and faecal water content were used to estimate retention of the administered fluids. Changes in acid base status were assessed from venous blood bicarbonate values. Fluid tonicity had a major effect on the uptake and elimination of the ORS. The hypertonic fluid (628 mOsm/kg bwt) was less rapidly absorbed and resulted in more rapid fluid and electrolyte excretion than the isotonic (314 mOsm/kg bwt) and hypotonic (water) fluids. The inclusion of glucose did not enhance the absorption of the ORS, although fluids containing higher concentrations of electrolytes resulted in more rapid elimination of fluid in urine. There was a direct relationship between higher concentrations of sodium in the ORS, plasma sodium values and osmolality. Fluid temperature (5, 21 and 37°C) had no demonstrable effect on absorption of the ORS and elimination of fluids post administration.

We concluded that while glucose concentration and fluid temperature have minimal effects on fluid absorption and elimination, fluid tonicity was a key element in the uptake and elimination of orally administered fluid. These findings are likely to be of relevance when administering ORS in association with exercise.
Sweating rate and sweat composition during exercise and recovery in ambient heat and humidity
Authors: McCUTCHEON L. J. , GEOR R. J. , HARE M. JESSIE , ECKER GAYLE L. , LINDINGER M. I.
Published: June 2010

The objective of this study was to determine the composition and extent of sweat losses during submaximal exercise under hot and humid conditions and to compare these findings with the same exercise protocol conducted under cool, dry and hot, dry conditions. Five Thoroughbred horses (age 3 to 6) completed exercise tests under each of 3 environmental conditions in random order: cool, dry (CD), room temperature (T) = 20°C, relative humidity (RH) = 45–55%; hot, dry (HD), T=32–34°C, RH=45–55%; and hot, humid (HH), T=32–34°C, RH=80–85%. Horses exercised at 50% of their predetermined V̇O2maxon a treadmill set at a 10% slope until attainment of a pulmonary artery blood temperature of 41.5°C followed by a 60 min recovery. Sweat was collected from a sealed polyethylene pouch enclosing a 150 cm2area on the lateral thorax. During exercise and the first 30 min of recovery, sweat fluid losses were 7.9 ± 0.7 litres, 9.9 ± 0.5 litres and 6.6 ± 1.2 litres (mean ± s.e.m.) for CD, HD and HH, respectively. Sweating rate (SR), calculated from sweat volume per unit area of enclosed skin, was lowest in CD and similar in HD and HH during exercise such that at end of exercise in HH (16.5 min) calculated sweat losses were approximately 5% and 32% higher than in HD and CD, respectively. In recovery, SR declined in all conditions but was significantly lower in CD (P<0.05). Sweating was detectable until 30 min recovery in CD, 45 min recovery in HD and 60 min recovery in HH. Sweat composition and osmolality was different under the 3 environmental conditions and changed gradually during exercise and recovery in all conditions. Osmolality and [Na] was highest in HD and lowest in CD. During exercise, [Na] increased with increasing SR. Although exercise duration was significantly decreased in HH (16.5 ± 1 min) when compared to HD (28 ± 2 min) and CD (37 ± 2 min), fluid and ion losses in HH were comparable to those in HD as a result of a high SR and prolonged sweating during recovery.
Redistribution of cardiac output in response to heat exposure in the pony
Authors: McCONAGHY FINOLA F. , HODGSON D. R. , ROSE R. J. , HALES J. R. S.
Published: June 2010

Radioactive microspheres were used to measure cardiac output and blood flow to most major tissues in 4 ponies at rest in thermoneutral (16°C/60% RH) and mildly hot (41°C/34% RH) environments. In response to heat stress there were increases in cardiac output (2‐fold), respiratory frequency (5‐fold), blood flow to the skin of the body (3‐fold), and limbs (50%), respiratory muscles (2‐fold) and the upper respiratory tract (3‐fold). Ponies were able to maintain body temperature in the hot environment by increasing blood flow to the tissues involved in heat dissipation, while blood flow to all other tissues remained stable. This was achieved by increasing the cardiac output without need for reduction of blood flow to other tissues.