Exercise physiology. An overview

Through the study of equine exercise physiology, one can learn more about what happens to the body of the performance horse during all forms of exercise. Better understanding of skeletal, joint, tendon, and ligament adaptations to loading and stress may allow adjustments to be made in training techniques to reduce the incidence of injury. The information obtained from exercise research may also facilitate the investigation of questions such as the following: What makes one horse perform better than another? How can one bring out the optimal performance in each horse? How can one tell when a horse has arrived at its peak performance capability? What are the factors that actually limit performance?     

Heart rate variability after horse trekking in leading and following horses

Horse trekking (HT) is having a stroll on a horse along a walking trail in a forest, field, and/or sandy beach. Generally in HT, horses exercise in tandem line outside the riding facilities. Because the leading horse will be confronted with stressors in the forefront, we hypothesized that the leading horse shows higher stress responses than the following one. In order to verify the hypothesis, we compared short‐term stress responses between each position in six horses. Exercise consisted of 15 min of ground riding and 45 min of HT with walking and trotting. Heart rate variability was analyzed for 5 min at 30, 60, and 90 min after the exercising period. There was no significant difference in heart rate during exercise between leading and following positions. The high frequency / low frequency power band of heart rate variability, an index of sympathetic nervous activity, after exercise, tended to be higher in the leading position than following one (P < 0.1). The result in this study can suggest that the leading horse was in a higher stressed state than the following horse after HT.     

How to Perform Transabdominal Ultrasound-Guided Fetal Fluid Sampling in Mares

Little is known about the composition and physiology of fetal fluids in all domestic mammals in comparison with humans, where the amniotic fluid has been the focus of numerous reports. Previously, in the horse, there have been concerns regarding the safety of fetal fluid sampling and the risks to the well-being of the fetus and techniques limitations that may preclude serial assessment. The objective of this report was to describe a transabdominal ultrasound-guided technique to safely perform multiple fetal fluid collections during the last trimester of gestation in mares. Similar methodology has been described previously; however, here we described step by step how to perform fetal fluid sampling. Several illustrative images have been included to facilitate the understanding of the technique by others lacking experiences with the procedures. In addition, small modifications on the sedation protocols and sampling have been performed in the present study. Six light horse mares carrying normal singleton pregnancies (260–280 days of gestation) were sampled three times at 5- to 7-day intervals (i.e., 0, 5, and 12 days). There were no apparent complications using the protocol described here. All mares delivered normal foals uneventfully. We foresee that the publication of this report may be useful to other research laboratories interested in studying the fetal fluids in mares, as well as in specific clinical evaluations of fetal well-being in research mares.     

Exercise in Thoroughbred yearlings during sales preparation: a cohort study

Reasons for performing study: There is increasing evidence suggesting that early exercise in Thoroughbred racehorses may be beneficial to the development of the musculoskeletal system. At present, information on the exercise programmes and health problems of individual yearlings during a sales preparation is scant. Objectives: To describe the exercise and health problems of Thoroughbred yearlings during preparation for sales, and to identify variations in exercise between and within farms. Methods: A prospective cohort study was used to collect exercise and health information from 18 farms across New Zealand. Daily exercise records for individual horses were recorded during the studfarms' preparation for the annual national yearling sales in January 2009. Results: Data were collected from 319 yearlings, of which 283 (88.7%) were exercised (hand walking, mechanical walker and lungeing) during their preparations. Sales preparation lasted a median of 69 days (interquartile range 61–78) and differed significantly between farms (P<0.001). The median exercise time performed differed significantly by gender (P<0.001), farm (P<0.001) and month of the preparation (P<0.001), but not by type of sale (P = 0.14) or category of sales price (P = 0.12). Within certain farms, daily exercise differed between horses as did total exercise by gender and the number of days spent in the sales preparation. Lameness was the most common condition affecting yearlings and the overall incidence rate of lameness was 0.08 per 100 horse days (95% confidence interval 0.05–0.13). Incidence rates of lameness varied significantly between farms (P = 0.02), but not by age (P = 0.77), sales type (P = 0.58) or month of the preparation (P = 0.53). Conclusions and potential relevance: Yearling exercise programmes varied between and within farms. Since exercise is already being tailored for each individual horse, there may be an opportunity to allow for modifications to sales preparation with the future career in mind.     

Dynamic epiglottic retroversion as a cause of abnormal inspiratory noise in six adult horses

This case report describes the endoscopic findings and outcome in 6 horses diagnosed with dynamic epiglottic retroversion (ER) during exercise. Horses included 2 showjumpers, one eventer, one pleasure riding horse and 2 Thoroughbred racehorses. All were adults (age range: 4–10 years). Dorsal angulation of the epiglottis was identified at rest in one horse. However, resting endoscopy was unremarkable in the remaining 5 horses. Exercising endoscopy was performed during high‐speed treadmill exercise in 3 horses and during ridden exercise in the other 3. Intermittent ER occurred during inspiration in all horses and the frequency increased with increasing speed. In 2 horses the epiglottis retroverted beyond the rima glottidis. All horses made an abnormal respiratory noise described as a ‘grunt’ when retroversion of the epiglottis occurred. Poll flexion was found to be an exacerbating factor in the nonracehorses. Two horses continued in work but abnormal inspiratory noise persisted. Surgical treatment, in the form of subepiglottic resection, was attempted in one horse. However, it never raced again after the procedure. Of the remaining horses, 2 were retired and the third was subjected to euthanasia.     

Effects of different forms of exercise on post inhibitory rebound and unwanted behaviour in stabled horses

Reasons for performing study: It is unknown if different locomotor activities are equally effective at meeting the stabled horse's need for exercise and if they attenuate unwanted behaviour. Hypothesis: Alternative forms of exercise influence the intensity of locomotor activities during a period of turn‐out (the so‐called rebound effect) and the occurrence of unwanted or undesirable activities during standard handling situations. Method: Twenty‐four horses kept in stables were randomly assigned to one of 4 exercise regimes (walker, treadmill, turn‐out and riding) for 4 consecutive days. Because these forms of exercise provide additional environmental stimulation, beyond that provided by exercise, each horse served as its own control in 4 corresponding (no exercise) control treatments presented in a balanced order. Unwanted behaviour was tested by taking horses to weighing scales and loading and unloading them onto a 4‐horse float by an experienced handler and the rebound effect was tested by releasing them into a large arena for a period of 15 min at the end of the exercise and control treatments. Results: Locomotor activities made up a large part of behaviour in the large arena following control treatments and all exercise regimes were sufficient to reduce the intensity of walking (P<0.05), trotting (P<0.01) and cantering (P<0.001) on release into a large arena. Exercise regime reduced the number of bucks (P<0.01) and rolling (P<0.05) during rebound tests suggesting that turn‐out was having a stronger effect than the other 3 exercise regimes. Exercise regimes significantly reduced the amount of unwanted behaviour and the number of commands given by the handler during weighing (P<0.05) but had no effect on these behaviours during loading onto a float. Conclusion: Providing stabled horses with one hour/day of exercise on a walker, treadmill, turn‐out or by being ridden are all effective at allowing expression of locomotor activities in stabled horses. Potential relevance: Providing stabled horses with regular exercise is likely to provide positive effects on horse welfare, training ability and handler safety.     

Treadmill exercise testing. Treadmill installation and training protocols used for clinical evaluations of equine athletes

The use of motorized treadmills has made it possible to evaluate equine poor performance with sophisticated diagnostic techniques during peak exercise. Treadmill exercise tests currently being used for clinical evaluations include treadmill gait analysis, dynamic hoof balancing, endoscopic evaluation of upper airway function, and exercise performance profiling. Large motorized treadmills (1 to 1.5 m in width and 4 to 5 m in length) are best suited for clinical evaluations. Ideally, the treadmill should be installed in-ground using a pit. This type of installation results in the tread surface being at the same level as the surrounding floor. A standard protocol should always be used to train horses to exercise on a treadmill. Training should be designed to introduce the horse to procedures required for a specific clinical evaluation gradually.     

Impedance plethysmography

The technique of impedance plethysmography is described and its application to observation of lung volume changes in the horse at exercise is discussed. The results from horse at rest show that there is a close relationship between rate of lung volume change (flow rate) and the associated impedance changes during both inspiration and expiration. Impedance changes during exercise were related to inspiration and expiration by observation of associated respiratory sounds. Artefacts related to technical difficulties are also indicated.     

Exercise and stress: impact on adaptive processes involving water and electrolytes

The horse has a regulatory system which responds in a complex manner to stress, such as exercise. It supplies the fuel and ensures thermoregulation, resulting in the production of sweat. Cutaneous water and electrolyte losses are controlled by thermoregulation, independent of hydration status and/or electrolyte homeostasis. The negative balance for water Na, K and Cl may be a factor in limiting performance and impairing recovery. The strategy in caring for a horse before, during and after exercise involves improving hydration and electrolyte status and the use of NaCl as a feed or in a watery solution (iso- or hypotonic). The voluntary intake of saline is not safe for any horse. If salt is supplemented in a feed, it is essential that water be made available ad libitum. It is also important that, after salt intake, sufficient time is allowed to give the horse the opportunity to drink an adequate quantity of water. Application of K prior to exercise is not recommended. During exercise, NaCl solutions can be administered, while salty supplements are less suitable as regard the time required to stimulate water intake. After exercise, K can be added to supplements or solutions to balance the K deficit.     

Cumulative racing-speed exercise distance cluster as a risk factor for fatal musculoskeletal injury in Thoroughbred racehorses in California

Thoroughbred racehorses which suffered a fatal musculoskeletal injury (FMI) while racing or race training at a California racetrack during 9 months of 1991 were studied to determine the importance of intensive, high-speed exercise schedules prior to injury. Seventy-seven horses which sustained an FMI while racing and 45 horses which sustained an FMI while race training were successfully matched by race or timed workout session with one control horse and included in the analyses. Race and timed workout (racing-speed exercise) histories were obtained for the case and control horses. Two-month cumulative, racing-speed cutoff distances were calculated from the control horse sample by two methods. Median racing-speed exercise frequencies and distances of the control horses were used to estimate age-specific (2, 3, 4 and ≥ 5 years), 2-month cumulative, racing-speed distances (Method 1). For the second method, the last race or timed workout for each control horse occurring just prior to, or on the date of injury for the matched case horse was identified. Cumulative racing-speed distances 2 months prior to these exercise events were determined for each control horse and used to estimate median age-specific (2, 3, 4 and ≥ 5 years), 2-month cumulative racing-speed distances (Method 2). The cumulative cutoff distances estimated from both methods were used to classify each matched pair according to the presence or absence of a 2-month cumulative, racing-speed distance which exceeded the age-appropriate cutoff distance (exercise distance cluster) within 6 months prior to injury. Manlel-Haenszel matched-pair odds ratios and 95% confidence limits were calculated separately for the racing and race-training fatal injuries. The relative risk for racing FMI was significantly greater for those horses which ran 2-month, cumulative racing and timed workout distances in excess of the cutoff values determined with Method 1 (relative risk (RR) = 3.0, 95% confidence interval (CI) = 1.2, 7.6) and Method 2 (RR = 7.2, 95% CI = 2.6, 20.6). The relative risk for race-training FMI was significantly greater for those horses which ran 2-month, cumulative racing and timed workout distances in excess of the cutoff values determined with Method 2 (RR = 3.4, 95% CI =1.0, 13.2).     

Method of investigation of the accuracy of four digitally-displaying heart rate meters suitable for use in the exercising horse

The measurement of heart rate during exercise in the horse has been recommended as a means of prescribing work effort, monitoring the changes in aerobic capacity during training and as part of the clinical examination of the performance horse. The accuracy of four heart rate meters (PEH 100, PU 10, HR 14 and HRM-7) was assessed by comparison with heart rate determined by simultaneous telemetry electrocardiography (ECG) using a rapid incremental exercise test on a treadmill. Heart rate displayed by all four meters showed significant correlations with the ECG heart rate, but only two meters (PEH 100 and HRM-7) had correlation coefficients of 0.98 or greater.     

The effect of exercise on blood metabolite levels in the horse.

The effects of exercise of different intensities on blood concentrations of glucose, lactate, pyruvate, free fatty acids and glycerol were studied in a group of clinically normal horses. Blood lactate, pyruvate and lactate/pyruvate ratio increased during exercise, particularly during galloping. These changes occurred within the first 12-15 seconds of exercise indicating that anaerobic metabolic pathways are brought into use very quickly in the strenuously exercising horse. Since blood glycerol levels were significantly increased during exercise body lipids were also mobilised. At the same time, free fatty acid levels increased during cantering but decreased during galloping indicating increased fat oxidation during strenuous exercise. It was concluded that both lipids and carbohydrates are as important energy sources in the exercising horse as in other species.     

Arterial blood gas tension and acid base balance during exercise in horses with pharyngeal lymphoid hyperplasia

Arterial blood gas and acid-base values during maximal exercise over a 1.2 km distance were recorded in four Thoroughbred horses before and after the chemical induction of pharyngeal lymphoid hyperplasia (PLH). Samples were collected after galloping 0.8 km and 1.2 km, immediately upon stopping and 5 mins after exercising. In only one horse was any difference noted in the pre and post PLH induction results. The horse was more hypercapnoeic at the 1.2 km mark and also took much longer to complete the gallop when it had PLH. However, it also had signs of lower respiratory disease. In the other horses, the only changes which could be attributed to PLH were seen immediately upon stopping. It seems that PLH does not inhibit gas exchange during exercise unless the lesions are extremely severe.     

Body fluids and exercise: Influences of nutrition and feeding management

Athletic performance may be initially enabled but then become limited by changes in body fluids. This subject is reviewed in three parts: physiological responses, replacement strategies, and the influences of nutrition and feeding management. Emphasis on losses in sweat during strenuous exercise have focused attention on replacement of water and electrolytes, but the economies of water and energy are intertwined, so our interest should expand to the whole diet and its management. Feed balanced for strenuous exercise must maximize the conversion of its potential chemical energy into kinetic mechanical energy, and minimize waste such as feces, acid and heat. Research suggests five efficiency promoting tentative features: strong cation-anion balance (200-300 mEq/kg dry matter); modest protein (80-100 g/kg); ample vegetable oil (100-120 g/kg); specified fibers (difficult to quantify simply); and a stress profile of other essential nutrients (tentatively 1.5- to 3-times higher than currently recommended on a digestible energy basis). In effect, such an ergogenic feed replaces starch and sugar with fat and fiber. A high fiber intake increases water intake, gut water and net water absorption during strenuous exercise. It also increases heat production and water needed for evaporation, bowel ballast and fecal water output. Feeding management before an event involves the timing, size and nature of meals and watering. It should be adapted to the individual horse during training. Our laboratory has developed two complete and balanced ergogenic feeds, one for the stall-kept athlete, the other for the horse on pasture. Use of high-efficiency feeds like these should enhance the homeostasis of body fluids during strenuous exercise.     

Treatment of radial fractures in adult horses: an analysis of 15 clinical cases

Fifteen cases of radial fractures in adult horses weighing more than 300 kg are discussed. Four of the horses were destroyed on humane grounds immediately because of a poor prognosis and expense of internal fixation; and two horses at five days and five weeks, respectively after treatment by cast application was initiated. Internal fixation was used in nine horses but of these only two horses recovered completely and resumed their former activities. In eight cases, two plates were applied, one lateral or medial and the other cranial. The internal fixation techniques of all nine horses were scrutinised and suggestions made for the future treatment of radial fractures. These suggestions are (1) the use of ASIF 5.5 mm cortical bone screws using the total width or thickness of the bone in each case. (2) Application of the dynamic condylar screw with its plate in distal or proximal fractures to allow more support. (3) Incorporation of a cancellous bone graft to the fracture. (4) Possible table recovery to prevent breakdown of the fixation during recovery. It is important that bone plates are applied over the total length of the bone. The fact that only two out of 15 horses survived and recovered completely underlines the problems associated with treatment of radial fractures in the adult horse.     

In vitro evaluation of nonrigid support systems for the equine metacarpophalangeal joint

Metacarpophalangeal (MCP) joint extension is primarily resisted by the digital flexor tendons and suspensory ligament. A variety of external support techniques are used to protect these supporting structures from or after injury by resisting MCP joint extension, although not all are effective and/or practical for use in an exercising horse. In this study, 7 forelimbs were loaded in vitro to determine the effect of a simple gamgee bandage, a 3-layered bandage with and without a contoured palmar splint, a neoprene exercise boot, and an innovative carbon fibre composite exercise boot (Dalmar tendon support boot). There was no significant resistance to MCP joint extension by the gamgee or neoprene exercise boot. The 3-layered bandage had a significant (P<0.01) supporting effect at MCP angles of > or = 245 degrees, and when combined with the contoured splint at angles of > or = 230 degrees. The Dalmar tendon support boot resisted MCP extension at angles of > or = 245 degrees (settings 1 and 2) and > or = 225 degrees (setting 3). These data demonstrate that the contoured splint and the Dalmar tendon support boot (which is also easily fitted for use during exercise) are useful for the management of tendon/ligament injury and during rehabilitation.     

Emotional Response to Novelty and to Expectation of Novelty in Young Race Horses

The aim of this study was to estimate the emotional response to novelty and to expectation of novelty in young race horses. The novelty in this study was the first training on an automated horse walker at a new training center. To estimate the level of emotionality in horses, the telemetric measurement of heart rate (HR) was used. A hypothesis was developed that expectation of novelty can be as exciting for horses as a novelty test. In this study, 40 horses were studied just before and then during their first walk on an automated horse walker. They were divided into four groups, with 10 horses in each group. These groups were as follows: (1) 1.5-year-old Thoroughbred colts, (2) 1.5-year-old Thoroughbred fillies, (3) 2.5-year-old Purebred Arabian colts, and (4) 2.5-year-old Purebred Arabian fillies. HR was measured at rest before exercise, during handling and moving the horse from the stable, while walking on the automated horse walker for about 20 minutes, while moving the horse from the walker to the stable, and at rest after exercise. HR response to the anticipation of novelty was higher in colts than in fillies, particularly in the group of Thoroughbreds.     

Improving a Complement-fixation Test for Equine Herpesvirus Type-1 by Pretreating Sera with Potassium Periodate to Reduce Non-specific Hemolysis

Non-specific hemolysis has often been observed during complement-fixation (CF) tests for equine herpesvirus type-1 (EHV-1), even when the sera have virus-specific CF antibodies. This phenomenon has also been reported in CF tests for various infectious diseases of swine. We found that the sera from 22 of 85 field horses (25.9%) showed non-specific hemolysis during conventional CF testing for EHV-1. Because pretreatment of swine sera with potassium periodate (KIO₄) improves the CF test for swine influenza, we applied this method to horse sera. As we expected, horse sera treated with KIO₄ did not show non-specific hemolysis in the EHV-1 CF test, and precise determination of titers was achieved.     

Body fluids and exercise: Replacement strategies

Athletic performance is initially enabled but then becomes limited by changes in body fluids. This review deals with potentially beneficial interventions replacement strategies. It is the second of a trilogy on exercise with a focus on body fluids. The first part (published previously in this Journal) concerned physiological changes in body fluids likely to affect performance. These changes are certain to tax the homeostatic capacity of a competitive horse, which may be supported by supplementation with water and electrolytes before, during or after an event. The simplest replacement strategy is to completely offset depletion, so as to maintain or restore the resting status. A preferred replacement strategy emphasizes more frequent and smaller doses during an event, so as to avoid over-riding the initial beneficial changes in body fluids. Because the turning points from enabling to limiting are not well established, effective electrolyte replacement currently depends as much on the rider's development of a specific dosage regimen (amounts and times) for an individual horse as on any scientist's rational design of a flexible formula for all horses.Marketedformulas are based on sweat loss and changes in plasma. Most contain Na, K and Cl; some also have Ca, Mg, P, glucose and nutraceuticals. Attention to hyperkalemia at speeds over 4 m/s suggests the need for two formulas—one without potassium for use during an event, the other with potassium for use before and after. Illustrative studies are examined for the validity of their physiological interpretations and their practicalimplications. They indicate various advantages from the administration of hypertonic mixtures of electrolytes in pastes or slurries a few hours before as well as during and after an event, provided that the horse has ample opportunity to drink. Nevertheless, the physiology of absorption suggests that hypertonic mixtures should be regarded as unsuitable for a clinically hypohydrated horse until shown otherwise. The third part of this series will discuss the influence of nutrition and feeding management on body fluids and performance.