Skeletal injuries in the equine athlete are a tremendous concern with both economic and animal welfare implications. As a result, much research has focused on improving bone quality through nutritional and exercise interventions. With the recent utilization of biochemical markers, changes in bone metabolism can be monitored. This study examined and compared the response of bone markers and estimates of bone mineral content, in studies with nutritional interventions, with those utilizing exercise interventions. The post hoc analyses suggest that nutritional interventions result in less change to bone markers and bone mineral content than exercise treatments. Of the bone markers examined, osteocalcin correlates most strongly to estimates of bone quality while keratin sulphate, an indicator of cartilage turnover, showed the least correlation. Comparing the results of this study with other published studies, similar findings were observed, suggesting that small alterations in exercise play a greater role in affecting measurable changes in bone metabolism and quality of the equine athlete than do small changes in nutrition.

Discussions on growing more durable equine athletes often revolve around developmental orthopaedic disease (DOD). What degree of DOD, if any, is acceptable or inconsequential to long-term athletic performance remains a question. Much effort has been directed toward diminishing or eliminating the incidence and severity of DOD, but with limited success. We must continue to define what degree the management decisions affect the horse during different stages of its growth. It would seem logical that the most profound influence would occur during the most rapid periods of growth. Therefore, concerns have been directed toward the last third of gestation and the possible indirect effect that broodmare management has on foetal development. The early postnatal period is another period of rapid growth; thus, the effect of broodmare management on lactation may affect the growth of the foal. Management will also have a direct effect on growth and development from weaning through to maturity. Recent research in other species as well as in horse suggests that genetic predisposition is the primary determinant of DOD. Non-nutritional management also may have significant effects on articular and skeletal health and athletic durability. Much effort has been directed toward nutrition and potential impact on DOD, but with limited success. Except for overt deficiencies, or perhaps excessive imbalances, nutrition does not appear to be a primary determinant of DOD, particularly of focal lesions associated with osteochondrosis. However, nutrition may serve a secondary role in diminishing the severity and incidence of DOD in horses genetically predisposed to such conditions. Producing horses that will have long-term and productive athletic careers requires sound management that starts at conception and continues throughout the life of the horse.

Methoxy polyethylene glycol–epoetin β (pegylated epoetin β, peg-epoetin β, Mircera®) is an erythropoiesis-stimulating agent that is synthesized by pegylating epoetin β. It is prohibited in racehorses and humans because it enhances their performance. It is detectable in human urine and plasma using the isoelectric focusing–double-blotting (IEF–DB) method that has been widely applied in human doping control laboratories to detect doping with recombinant erythropoietins (EPOs). Fifty micrograms of peg-epoetin β were administered intravenously to a 450 kg female Thoroughbred, and blood was collected for 48 h. The plasma was processed by immunopurification followed by IEF–DB. The analytical procedures required about 2 days. No peg-epoetin β was detected in the baseline plasma collected prior to drug administration. It was readily detected in samples collected at 2, 4, 6, 8, 24 and 48 h. The isoforms showed a characteristic pattern that differed from epoetin β and was unlike any other known erythrocyte-stimulating agent or recombinant EPO. No peg-epoetin β was detected in plasma from five control horses. The plasma samples were also tested by a rapid, automated and chemiluminescent immunometric assay for EPO (Immulite®). The samples collected from the treated horse at 2–48 h contained the equivalent of approximately 200–800 pg ml− 1 of peg-epoetin β. The samples from the ten control horses were negative. These data show that a small dose of peg-epoetin β is detectable for 48 h by two different methods that are based on two different principles (chemiluminescence immunoassay and IEF–DB). The Immulite® assay is suitable as a screen and the IEF–DB assay as a confirmation method. These studies need to be expanded to other horses. The screen and confirmation tests, if applied, will probably eliminate the use of peg-epoetin β as a horse doping agent.

This study tested the hypothesis that phenylbutazone would block the exercise-induced increase in cytokine markers of inflammation in blood. Blood samples were obtained from unfit Standardbred mares (age 10 ± 4 years, ~500 kg) before and after three different trials (standing control (CON), n = 9; exercise with phenylbutazone (EX-bute), n = 9; and exercise with water, n = 9). Comparisons were made for data collected in three trials, one where each horse underwent an incremental exercise test (graded exercise test (GXT)) where they were administered water as a placebo, a GXT following phenylbutazone administration (2 g given orally 2 h before the GXT) or standing parallel control where they stood quietly in stalls. During the GXT, horses ran on a treadmill (1 m s− 1 increases each min until fatigue, 6% grade). Blood samples were obtained 30 min before exercise, immediately after exercise and at 0.5, 1, 2, 4 and 24 h post-GXT or at matched time points during the parallel control trials. Samples were analysed using real-time PCR for measurement of mRNA expression of interferon-γ (IFN-γ), tumour necrosis factor-α (TNF-α) and interleukin (IL)-6 in samples collected during all three trials, and for IL-1 and IL-10 in samples collected for the CON and EX-bute trials. Data were analysed using ANOVA for repeated measures, and where appropriate, post hoc separation of means utilized the Student–Newman–Keuls test. The null hypothesis was rejected when P < 0.05. There were no changes (P>0.05) in IL-1, IL-6, IFN-γ or TNF-α during CON or following phenylbutazone administration. During the water trial, exercise resulted in significant increases in IFN-γ, IL-1 and TNF-α. It was concluded that high-intensity exercise results in a transient increase in the expression of inflammatory cytokines in blood that is blocked when phenylbutazone is administered to horses.

While temporal variable measurements have assisted in objectively defining and distinguishing between four-beat stepping gaits performed by gaited horses, kinematic research describing joint motion of the gaited horse is limited. The objective of this study was to measure the temporal variables and the forelimb kinematics of the flat walk and fox trot of the Missouri Fox Trotter (MFT) to provide a more comprehensive description of these gaits and to assist in distinguishing between them. Reflective markers placed along the lateral aspect of the right forelimb and the zygomatic process of the temporal bone were tracked at 60 Hz as eight MFTs were ridden at a flat walk and fox trot for ten strides. Student's paired t-tests were performed to compare means of analysed parameters between gaits on finding that the fox trot was a faster stepping gait (fox trot velocity: 3.17 ± 0.03 m s− 1, flat walk velocity: 1.75 ± 0.06 m s− 1) with a shorter stride duration (fox trot: 0.63 ± 0.03 s, flat walk: 1.17 ± 0.06 s) and greater stride frequency (fox trot: 1.59 ± 0.09 strides s− 1, flat walk: 0.09 ± 0.04 strides s− 1) than the flat walk (P < 0.05). Both gaits were performed with similar stride length (fox trot: 2.0 ± 0.03 m, flat walk: 1.95 ± 0.05 m), but the fox trot had an irregular rhythm with diagonal couplets (diagonal advanced placement: 0.10 ± 0.01 s, lateral advanced placement: 0.23 ± 0.02 s). Vertical head excursions, protraction/retraction angles and joint angle-time curves for the shoulder, elbow, carpus and forelimb fetlock were similar between gaits. Shoulder peak flexion of the fox trot occurred later in the stride (fox trot: 38 ± 5%, flat walk: 20 ± 3%; P < 0.05), but the timing of the other peak flexion and extension joint angles were similar between gaits. The fox trotting carpus flexed more (fox trot: 136 ± 3°, flat walk: 147 ± 4°) than the carpus of the flat walk (P < 0.05), but the other peak flexion and extension joint angles were comparable between gaits. Measured temporal and kinematic variables assisted in defining the fox trot and flat walk and differences between variables can be applied in distinguishing between the two gaits.

Nutritional management studies to improve the performance of Mangalarga Marchador (MM) horses during the marcha test are limited. This study was designed to test the hypothesis that chelated trivalent chromium (CR) feed supplementation may reduce the suitability of the length of the interval between concentrate feeding and the marcha test among MM horses. A total of 12 healthy mares (4.25 ± 0.62 years) were randomly assigned to one of six dietary treatments (0 or 10 mg Cr by concentrate, fed 0.5, 2 or 4 h before exercise), according to a completely randomized design, with a split-plot arrangement. The diet was Cynodon pasture and concentrate (50:50 ratio). The first 29 days of the trial were for diet, Cr and exercise adaptation; during the next 15 days, horses were submitted to three 50-min field marcha tests, once a week. Heart rate (HR) was measured before, during and until 25 min after the exercise. Respiratory rate and rectal temperature were measured; blood samples were collected before, at the end and 25 min after the test. There was no effect of Cr by concentrate feeding strategy on any physiological variables (P>0.05). Supplementation of Cr increased glycaemia before and soon after the second marcha test (P < 0.01). In addition, Cr reduced HR during the second marcha test and decreased the time to first post-exercise HR recovery (P < 0.05). Insulinaemia was greater when the concentrate was provided 2 h prior to the test (P < 0.05). Concentrate provided 0.5 and 2 h before the test reduced plasma triacylglycerol in the first and second tests, respectively. The interval between concentrate feeding and marcha tests should not be decreased in horses supplemented with Cr. Horses should be fed more than 2 h before that test. Cr supplementation during training may improve the cardiac performance of MM mares during the marcha test.

The tension applied to the girth is usually based on an individual's experience rather than by scientific measurement or procedure. The equine thorax is a dynamic structure, and therefore the actual readings of girth tensions at rest and during exercise (actual tension) are likely to vary from the tension to which the girth was intended to be tightened at rest while standing (intended tension). This study was undertaken to determine the variability of girth tensions at rest and during exercise. A total of 19 Hanoverian horses were lunged on a 20 m circle in walk, trot and canter on both reins. In a randomized design, each horse was exposed to intended tensions 6, 10, 14 and 18 kg (saddle and girth at appropriate intended tensions). Girth tension was measured and recorded continuously using an in-line load cell. Intended girth tensions were not significantly different with mean actual girth tensions while standing. Actual girth tensions increased significantly (P < 0.001) between walk, trot and canter at all tensions except rest to trot at tension 6 kg, where the significance level was P < 0.01. Actual girth tension was significantly higher (P < 0.001) on the left rein at tension 14 kg in walk and trot, and at tensions 6, 10 and 14 kg during canter, and there was an overall trend for higher actual girth tensions on the left rein for the other tensions. As the thorax is a dynamic structure, girth tension variation could be due to multiple factors such as respiration, breath holding, muscular contraction, back flexion and extension, speed, gait and vertical acceleration of the saddle. Girth tension is a relatively new area of research, and as there are many opportunities for further research, a better understanding of the impact the girth has on the horse could help to improve performance and welfare.

Successful completion of endurance exercise is facilitated by conditioning that enhances the capacity of the cardiovascular and musculoskeletal systems to maintain a high level of aerobic activity. Insufficiency or disease in these systems may be diagnosed using routine haematology and serum chemistry testing. Pre-race blood samples obtained from 82 endurance-trained sled dogs were used to test the hypothesis that common haematological and serum chemistry values could identify subjects with occult disease, decreasing the likelihood of their finishing a multi-day exercise challenge. Multivariate logistic regression was used to identify the combinations of specific biomarkers that best predicted the eventual outcome of the exercise challenge for an individual dog. This analysis constructed six different predictive formulas. In all cases, the formulae contained the pre-race values for creatine kinase and some measurement of erythrocyte abundance. When a probability of 0.4 was used as a cut-off value, all dogs with values below the cut-off did not complete the race. These results suggest that in a population of healthy, aerobically conditioned subjects, routine clinical biomarkers can be used to identify subjects unsuited to performance for endurance exercise.

The impact of body density (BD) on an animal's capacity to sustain a workload is important in the accuracy of evaluating swimming exercise in rats and the associated training protocols. The aim of this study was to quantify the influence of BD the maximal lactate steady-state (MLSS) workload in swimming rats. The BD of ten 90-day-old rats and sixteen 120-day-old rats was determined by underwater weighing, and their aerobic capacity was determined by the MLSS test. The MLSS blood concentration values were 4.11 ± 0.96 mmol l− 1 in the 90-day-old rats and 4.81 ± 1.49 mmol l− 1 in the 120-day-old rats. There was no significant (P>0.05) difference between these values. The older rats were more dense (P < 0.001) and showed a significantly increased (P < 0.001) absolute effort and relative-to-body-weight effort to keep themselves on the water surface when compared with the younger rats. BD can significantly affect an animal's capacity to sustain work within this age range, and individual fluctuation in effort should be determined to avoid mistakes when interpreting the results. This is particularly important in longitudinal studies in which the intervention or ageing process can modify the animal's body composition. Our results quantify the effects of BD on the performance of rats in the MLSS test.

The assessment of the effect of race training on the locomotory apparatus can be confounded by tissue responses to the increasing training load, such as dorsal metacarpal disease. The aim of this paper was to examine the changes in gait during the early stage of race training in a cohort of 19.2-year-old Thoroughbreds, 11 of which had previously been exposed to spontaneous pasture exercise and also to preconditioning exercise from an early age (CONDEX), and the remainder had been exposed to only spontaneous pasture exercise (PASTEX). Data were collected 52, 60, 77, 109 and 176 days after the horses had entered the racing stable. At each examination, the horses were trotted in-hand on a hard asphalt surface, and kinematic data were collected. The horses trotted slowest on the first examination day, with a significantly longer and slower stride and associated percentage stance time. On day 77, the CONDEX horses trotted faster, had a longer stride length and achieved mid-stance earlier than the PASTEX horses. Across both groups, the introduction of galloping was associated with a significant reduction in stride duration (0.69 ± 0.01 vs. 0.66 ± 0.01 s, P = 0.001), stride length (2.49 ± 0.03 vs. 2.38 ± 0.02 m, P = 0.004) and stance duration (27.3 ± 1.0 vs. 32.0 ± 1.0%, P = 0.001). The changes in gait appeared to be associated with the introduction of galloping and the associated tolerance of the CONDEX group to the musculoskeletal loading.

This study was designed to determine the effect of 200 ml of autologous blood instilled in the lungs of healthy horses had on gas exchange, maximal oxygen consumption and breathing mechanics during supramaximal exercise, as a model of exercise-induced pulmonary haemorrhage (EIPH). The subjects were six healthy well-conditioned Thoroughbred horses. On four occasions over a 6-week period, six horses were subjected to two bouts of exercise to fatigue per day, each at speeds equated with an oxygen requirement that was 110% of . Prior to the second bout of exercise on each day, the horses underwent bilateral bronchoscopy during which either nothing (control), or 200 ml of saline, plasma or blood was inoculated into the distal airways, divided equally between each lung. Run time to fatigue, and measurements of pulmonary gas exchange and breathing mechanics were made and analysed for the effects of the four treatments (control, saline, plasma and blood). Inoculation of blood significantly reduced pulmonary oxygen exchange, and run time to fatigue. Plasma inoculation caused intermediate effects, adversely affecting arterial oxygen tension but without significantly reducing or run time to fatigue. Saline treatment had no effect. None of the treatments had an effect on ventilatory mechanics. The results of this study suggest that volumes of blood in the order of 200 ml can impair gas exchange and interfere with the ability of horses to exercise at supramaximal intensities. Blood volumes of this magnitude are readily evident endoscopically, and probably reflect a moderate-to-severe level of EIPH, in contrast to previously published studies where the unilateral instillation of 100 ml of blood or less did not affect performance.

The study undertook comparative analysis of horse gender and eventing performance. Limited previous research has investigated the impact horse gender may have on performance. However, many competitors have a preference for one gender over another (normally geldings). The study sampled five levels of the sport (intro, pre-novice, novice, intermediate and advanced) and investigated dependent variable penalty scores within the dressage, show jumping and cross-country phases; additionally, final penalty score, rank in competition and lifetime score were analysed. Results indicated the effect of gender to be limited. Issues relating to sample size, data structure and scoring mechanisms are discussed further.

Intense exercise has been associated with free radical damage that forms potentially measurable by-products in the blood and muscle of exercising subjects. The extent of damage to the exercising animal has yet to be conclusively determined, and studies often focus on by-products in the blood rather than muscle. The current study examined the presence of oxidative products in the muscle of exercising horses as well as the effects of excess vitamin E on the presence of these products. Eight Thoroughbred horses were used in a crossover design, with one group being fed vitamin E at the 1989 NRC [National Research Council (1989) Nutrient Requirements of Horses. 5th revised edn.; Washington DC: National Academy Press, pp. 48] level recommended for horses in moderate to intense work (80 IU kg DM− 1), and the second group being fed the control diet plus 3000 IU day− 1dl-α-tocopheryl acetate. The horses underwent an 8-week training programme and a final standard exercise test (SET). During the SET, the horses ran on a 6° incline to exhaustion. Muscle samples were biopsied before and after performing the SET and analysed for the presence of carbonyl groups and ubiquitin. Blood was collected prior to the SET and analysed for vitamin E. No significant differences in plasma vitamin E were found between treatment groups. However, myofibril carbonylation, a product of free radical damage to muscle tissue, was found to be lower in vitamin E-supplemented horses post-SET exercise (P < 0.05), suggesting that vitamin E influences some measures of oxidative stress in exercising horses, particularly following a strenuous bout of exercise. Ubiquitin was not detected in myofibrils, indicating clearance of carbonyl groups by a different mechanism.

The purpose of this study was to test the hypothesis that the gastric ulcer medications, ranitidine and omeprazole, would alter plasma concentrations of total carbon dioxide (tCO2), lactate (LA), Na+, K+, Cl−  and total protein (TP), as well as calculated plasma strong ion difference (SID) and packed cell volume (PCV) in horses subjected to a simulated race test (SRT). Twelve unfit Standardbred mares (~520 kg, 9–18 years) were used in a randomized crossover design with the investigators blind to the treatment given. Each mare received a treatment three times daily (TID) at 06.30, 12.30 and 18.30 hours. The treatments administered orally were omeprazole (4 mg kg− 1 was given in the morning with apple sauce given at the later, two dosing times to encourage good behaviour), ranitidine (6 mg kg− 1 crushed and mixed in 20 ml apple sauce) and control (20 ml apple sauce TID). Each horse completed a series of SRTs with blood samples taken via jugular venipuncture at five intervals (prior to receiving treatment, prior to SRT, immediately following exercise and at 60 and 90 min post-SRT). During the SRTs, each horse ran on a treadmill fixed on a 6% grade for 2 min at a warm-up speed (4 m s− 1) and then for 2 min at a velocity predetermined to produce VO2max. Each horse then walked at 4 m s− 1 for 2 min to complete the SRT. Plasma tCO2, electrolytes, LA and TP concentrations and PCV–TP were measured in duplicate at all intervals. No differences (P>0.05) were detected between control, ranitidine or omeprazole for any of the measured variables. There were differences (P < 0.05) in tCO2, SID, PCV, TP, LA and electrolyte concentrations relative to sampling time. However, these differences were attributable to the physiological pressures associated with acute exercise and not an effect of the medication. It was concluded that ranitidine or omeprazole did not alter plasma tCO2 concentration.

Twenty-seven mature Standardbred mares (9–27 years, ~522 kg) were used to test the hypothesis that training and short-term cessation of training would alter total plasma total carbon dioxide (tCO2) concentrations. Plasma tCO2 concentrations were measured in blood samples (20 ml) collected at rest from the same ten unfit mares that were used in two separate studies that were conducted 1 month apart. Comparisons between the samples obtained from the two trials were made to demonstrate the consistency of plasma tCO2 concentrations in the untrained population. Another set of resting blood samples was collected from an additional 17 mares that were being utilized in a training study that was under way during the same period. All the mares were housed in groups on dry lots, and were fed approximately 12 kg of mixed alfalfa-grass hay divided into two feedings per 24 h period. During the ‘detraining’ period, the 17 horses were housed in 5 × 5 m stalls, and were fed the same hay ration. Water and trace-mineral blocks were available ad libitum. Blood samples were collected from the mares prior to the last session of their 12 weeks of training at 60% HRmax (maximum heart rate), as well as on the third day following 2 days of detraining (simulated quarantine). Plasma tCO2 concentrations were measured in duplicate using a Beckman EL-ISE analyser. For data analysis, t-tests with the a priori level of statistical significance set at P < 0.05 were used. Resting plasma tCO2 concentrations were lower (P < 0.05) in the trained horses (31.4 ± 1.9 mMol l− 1) than in the untrained horses (34.4 ± 0.9 mMol l− 1). There were no effects (P>0.05) due to cessation of training. It was concluded that training causes a decrease in plasma tCO2 concentrations that is not reversed by limited cessation of training.

An innovative exercise machine, which mimics the movement of horseback riding, has been made available in the market. As an initial step in characterizing this device, we determined the cardiovascular and metabolic responses to exercise. Twenty apparently healthy subjects rode the device (Equus) on day 1. The upper body exercises were added on day 2, to see whether cardiac and metabolic demands were further elevated (Equus+aerobics). After 10 min of continuous exercise, oxygen consumption increased significantly. In the Equus+aerobics condition, increase in oxygen consumption was significant as early as 4 min into the graded exercise test. Overall oxygen consumption was greater in the Equus+aerobics condition than in the Equus condition (P < 0.05). Oxygen consumption returned to baseline levels within 1 h after the Equus (190 ± 58–188 ± 50 ml min− 1) and Equus+aerobics (198 ± 54–194 ± 43 ml min− 1) conditions. Heart rates increased gradually during the graded exercise tests in both conditions (64 ± 11–78 ± 15 and 65 ± 11–83 ± 12 bpm in the Equus and Equus+aerobics conditions, respectively). Both systolic and diastolic blood pressure (BP) increased significantly 6 min into the graded exercise tests and remained elevated throughout exercise in both the conditions. There were no significant differences in BP responses between the two conditions. These results indicate that the cardiac and metabolic stresses achieved with this exercise device are small.

The exchange of water between plasma and interstitial fluid (ISF) along the length of a capillary is attributed to a balancing of the Starling forces, site-specific differences in hydrostatic and osmotic pressures that theoretically determine directional fluid movement. The osmotic forces for water movement are attributed to the osmotic effects of proteins, colloid osmotic pressure (COP). Several physiological inconsistencies question the role of proteins and COP in fluid flux. A reconsideration of Hulett's insights concerning the osmosis of water provides substantial evidence that the effect of COP does not cause osmosis, and therefore another force is needed to explain plasma–ISF exchange. Review of whole-body tissue and blood ion concentrations and/or ion differences across isolated tissue or secretory epithelia from a variety of species indicates that the diffusion of bicarbonate and strong ions within plasma is the dominant osmotic effect returning ISF to the capillary. Conceptually, as these ions diffuse along physiological gradients, they alter the chemical potential of water through which they are diffusing (solute–solvent drag), creating an osmotic effect on plasma water, and explain plasma–ISF exchange. Considering venous–arterial differences, diffusing and strong ions give rise to a net osmotic force (~35 Torr) in venous end capillary plasma water that is coupled to ISF through pores in the endothelium. More importantly, diffusing and strong ions provide an incremental osmotic force (~150 Torr) that is essentially matched to any change in metabolic rate (e.g. muscular work) when CO2 output and water production are increased. The proposed diffusing ion osmotic force does not negate the necessity for colloidal proteins in volume regulation. Proteins can have an essential effect on fluid exchange in plasma when blood flow is intermittent or changes in protein concentration in the ISF such that proteins exert a force against a distensible boundary (i.e. the endothelium and basement membrane) as they are reflected by it or diffuse through the membrane due to changes in permeability.

Some of the clinical signs seen in horses during endurance races may result from increases in neuromuscular excitability and are related to plasma [K+] and [Ca++]. The present study aimed to test the following hypotheses: (1) Potassium supplementation will affect plasma [K+] and may result in clinical signs related to neuromuscular hyperexcitability during an 80 km endurance ride. (2) Plasma [Ca++] will reflect dietary cation–anion balance (DCAB) and calcium intake. Feeding with a high DCAB and high dietary calcium content (1.5% total calcium of daily ration) diets would lead to higher plasma [Ca++] during an endurance race than on feeding high DCAB diets with a moderate dietary calcium content (1% of total calcium of daily ration). The current study was undertaken during the 80 km endurance research ride in 2002 in Virginia, USA. Forty volunteer rider–horse pairs participated in the race. During the race, electrolyte mixtures with (EM+K) and without (EM − K) potassium were supplied to 18 and 22 horses, respectively. After the race, the horses receiving EM − K during the race were supplied with a recovery formula containing potassium (EM-REC). The horses were fed in addition to their own forage (hay and pasture) either their own commercial concentrate (CC; 1% calcium, n = 11) or one of two research-supplied concentrates during 3 months preceding the research ride, one concentrate rich in sugar and starch (SS; 2% calcium, n = 15) and the other rich in fat and fibre (FF; 2% calcium, n = 14). Peripheral blood samples were taken the day before, within 3 min of the arrival at the vet checks at 27, 48 and 80 km, and after 3 h of recovery. Plasma samples were analysed for pH, haematocrit (Hct), [Na+], [K+], [Cl− ], [Ca++], [Mg++], total protein (TP) and albumin [alb]. Effects of sampling times, treatments and interactions were evaluated by ANOVA in a mixed model with repeated measures and applied to the 25 horses that completed 80 km. Eliminated horses had their blood sampled before entering the elimination vet check and 3 h after elimination, and were compared with finishing horses by t-test. As the ride progressed, significant increases were found in plasma pH, [Na+], , [TP], [alb], Hct and osmolality; and decreases in [K+], [Mg++], PCO2, [Ca++] and [Cl− ]. Horses supplied with potassium-free, sodium-rich electrolyte formulae (EM − K) had 12.5% lower (P = 0.001) mean plasma [K+], 7.8% lower (P = 0.024) TP and 8.4% lower (P = 0.004) albumin at 80 km, and at 3 h after the race they had 6.8% lower (P = 0.045) TP, when compared with EM+K supplemented horses. Horses fed with SS and FF had higher [Ca++] at 27 (P = 0.027), 56 (P = 0.006) and 80 km (P = 0.022) when compared with horses fed with CC. The lower [K+] in the EM − K group, and the higher [Ca++] in the SS- and FF-supplemented horses may help prevent increases in neuromuscular excitability and related clinical signs. The lower TP and albumin indicate less dehydration in the EM − K group and could help prevent related disorders.

A kinematic multi-planar analysis (MPA) reduces a subject's three-dimensional motion to two-dimensional projections onto planes defined by a fixed global coordinate system (GCS). An alternative to this kinematic method is a joint coordinate system ( JCS) that describes the three-dimensional orientation of the segments comprising the joint with respect to each other so that the JCS moves dynamically with the horse's anatomy. Therefore, the objectives of this study were to locate where differences may occur between the joint motion measurements made using MPA and those made using JCS and to document why these differences in measurements may occur. A Peruvian Paso was recorded during six walking trials using 60 Hz video camcorders. Skin markers tracked the movements and defined the anatomical axes of antebrachial, metacarpal and proximal phalangeal segments. A JCS was established between the two segments comprising the carpal and fetlock joints to measure flexion/extension, internal/external rotation and adduction/abduction at each joint. The MPA model used two markers aligned on the long axis of each segment and measured flexion/extension angles projected onto the sagittal plane of the coordinate system and adduction/abduction angles projected onto the frontal plane of the coordinate system. Carpal and fetlock flexion/extension angles for the walk were similar for the JCS and MPA (peak absolute difference: carpal joint = 7 ± 4° and fetlock joint = 7 ± 2°), indicating that sagittal plane analysis using MPA is adequate when flexion and extension are the only measurements being made provided the horse's plane of motion is aligned with the plane of calibration. There were relatively larger differences in carpal and fetlock adduction/abduction angles measured using an MPA compared with a JCS. Peak absolute difference between the JCS and MPA adduction/abduction angles occurred at 53% of the stride for the carpus (17 ± 4°) and at 61% of the stride for the fetlock (123 ± 25°). Analysis of the reasons for these differences indicated that the accuracy of frontal plane analysis to measure adduction/abduction is limited by its inability to correct for out-of-plane rotations along the long axis of the segments comprising the joint.

This study tested two hypotheses. First, that moderate exercise would alter maternal and foetal heart rate (HR) in the horse. Second, that pregnancy would alter the HR, plasma cortisol and plasma lactate response to moderate exercise in mares. Six unfit, pregnant Standardbred mares (6–19 years) underwent two incremental graded exercise tests (GXT). The first GXT was performed at approximately 9 months of gestation, which represents c. 80% of the total pregnancy time, and the second GXT at approximately 6 months post-parturition. During the GXT, mares ran on a treadmill up a fixed 6% incline completing three 1 min steps at velocities of 4, 6 and 7 m s− 1. Maternal HR was obtained via both electrocardiograph (ECG) and the ventricular waveform obtained from a micromanometer catheter. Data were recorded at rest, at 4, 6 and 7 m s− 1 of the GXT and at 0, 1, 2, 3, 4 and 5 min post-GXT. Foetal HR rate was measured via ECG before, immediately after and at 1, 2, 3, 4 and 5 min post-GXT. Radioimmunoassay (RIA) kits were used to measure plasma cortisol concentration in samples collected before the GXT, immediately after exercise and after 5 min of recovery. Plasma lactate concentrations (LA) were measured at rest, at 4, 6 and 7 m s− 1 and at 5 min post-GXT. Plasma cortisol concentrations were measured using RIA and the samples collected at rest, immediately after and at 5 min post-GXT. Exercise caused no change (P>0.05) in foetal HR. Maternal HR, plasma LA and plasma cortisol concentration were greater (P < 0.05) during the post-parturient GXT compared with the pre-parturition GXT. Body weight (mean ± SE) was lower after parturition (570 ± 20 vs. 505 ± 22 kg; P < 0.05). Consequentially, there were differences (P < 0.05) in work rate (watts) at each step of the GXT (1557 ± 53 vs. 1381 ± 60; 2339 ± 80 vs. 2071 ± 90; and 2571 ± 121 vs. 2416 ± 105 W). These data suggest that mares benefit from greater cardiovascular efficiency during pregnancy. Additionally, the lack of a change in foetal HR suggests that the unborn foal is not stressed during moderate maternal exercise.