An energetic basis of equine performance

Thermodynamics of Animal Locomotion

Muscles are biological actuators extensively studied in the frame of Hill's classic empirical model as isolated biomechanical entities, which hardly applies to a living organism subjected to physiological and environmental constraints. Here we elucidate the overarching principle of a living muscle action for locomotion, considering it from the thermodynamic viewpoint as an assembly of actuators (muscle units) connected in parallel, operating via chemical-to-mechanical energy conversion under mixed (potential and flux) boundary conditions. Introducing the energy cost of effort as the generalization of the well-known oxygen cost of transport in the frame of our compact locally linear nonequilibrium thermodynamics model, we analyze oxygen consumption measurement data from a documented experiment on energy cost management and optimization by horses moving at three different gaits. Horses adapt to a particular gait by mobilizing a nearly constant number of muscle units minimizing waste production per unit distance covered; this number significantly changes during transition between gaits. The mechanical function of the animal is therefore determined both by its own thermodynamic characteristics and by the metabolic operating point of the locomotor system.

Physiological response to an experimental 100 m flying pace race in Icelandic horses and effect of rider

This study evaluated the physiological response to an experimental 100 m flying pace race (EPR) in Icelandic horses with pace-competition experience, and whether there was an effect of rider. A cross-over design with nine horses and two riders was used. The EPR was performed twice (once with each rider) with four days of rest in-between. The EPR consisted of two runs (I and II), of which at least 100 m was in pace at full speed according to international competition rules. Plasma lactate concentration increased and was greater after pace run II than I (18.5±1.3 vs 11.9±0.7 mmol/l; P<0.001). Heart rate was higher during pace run I than II (207±3 vs 205±3; P=0.02). Heart rate and Lact had not recovered 30 min post exercise but Hct was back to resting level after 30 min recovery. Speed did not differ between riders and pace runs (pooled mean ± standard deviation of pace runs: 10.4±0.7 m/s, range 9.2-12.1 m/s) but HR and Lact were higher from warm-up and until 30 min recovery with rider 1 than 2 (P<0.001). There was a negative correlation between post EPR Lact with rider 1 and previous best record (r2=0.72, P=0.032). To conclude, a 100 m flying pace race in the Icelandic horse is a high-intensity exercise and anaerobic metabolism is crucial for performance. The rider had an effect on the physiological response but it is unclear if it was due to body weight, riding style or both. The practical relevance of the differences observed between riders remains to be proven but our results indicate that they may have limited impact on single day competitions since the speed was the same with the two riders.

Putative regulation mechanism for the MSTN gene by a CpG island generated by the SINE marker Ins227bp

Background

A single nucleotide polymorphism (SNP) in the first intron of the myostatin gene (MSTN) is associated with aptness of elite Thoroughbreds to race over sprint, middle or long distances. This intronic marker (g.66493737 T ≻ C), a short interspersed nuclear element (SINE) of 227 bp (Ins227bp) insertion polymorphism in the MSTN promoter, and the adjacent SNP BIEC2-417495 have not been studied for their association with racing aptness of the average Thoroughbreds raced in countries with lower status of the racing industry. This study investigated these markers regarding their prevalence and association with performance in common race horses. Markers were genotyped by amplification refractory mutation system-quantitative PCR (ARMS-qPCR) or amplicon melting. Furthermore, we asked whether the Ins227bp marker might theoretically regulate the expression of myostatin by generating a novel target for DNA methylation or by changing binding sites for transcription factors. Putative sites for DNA methylation or binding of transcription factors were predicted by MethPrimer and by the softwares JASPAR, MatInspector and UniPROBE, respectively.

Results

Pairwise linkage disequilibrium between g.66493737 T ≻ C and Ins227bp was high (r² = 0.93). A lower linkage was determined for g.66493737 T ≻ C and BIEC2-417495 (r² = 0.69) as well as for BIEC2-417495 and Ins227bp (r² = 0.76). The estimated frequencies for the presence of Ins227bp (I) indel and the C alleles at g.66493737 T ≻ C and BIEC2-417495 were 0.46, 0.47 and 0.43, respectively. Heterozygotes represented the most abundant genotype at each locus. The best racing distance (BRD) was significantly different between the homozygotes of each SNP (p = 0.01 to 0.03). C allele homozygotes at BIEC2-417495 or g.66493737 T ≻ C, as well as Ins227bp homozygotes earned most money on a mean distance ranging from 1211 to 1230 m. Heterozygotes earned most money on races over 1690 to 1709 m. The BRD for the T/T carriers at both SNP loci and for the SINE-free genotype was 1812 to 1854 m. Other performance parameters were not significantly different between the genotypes, except of the relative success score (RSS). The RSS was significantly slightly better on a distance of ≤1300 m for all carriers of the C allele and the Ins227bp compared to homozygous T genotypes and SINE-negative horses (p = 0.037 to 0.046). For distances of more than 1300 m the RSS was not significantly different between genotypes.

In silico assessment indicated that the Ins227bp promoter insertion might have generated a CpG island and a few novel putative binding sites for transcription factors.

Conclusions

All three target polymorphisms (Ins227bp, g.66493737 T ≻ C, BIEC2-417495) are suitable markers to assess the ability of non-elite Thoroughbreds to race at short or longer distances. The CpG island generated by Ins227bp may cause training-induced silencing of MSTN expression.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-015-0428-3) contains supplementary material, which is available to authorized users.

The effect of exercise regimens on racing performance in National Hunt racehorses

REASONS FOR PERFORMING STUDY

A previous study has identified exercise undertaken during training to be associated with racing performance in flat racehorses. However, no such studies have been conducted in National Hunt (NH) horses.

AIM

To determine whether exercise undertaken during training is associated with racing performance in NH racehorses.

METHODS

Data were collected as part of a larger study investigating injury occurrence in NH racehorses. Race records and daily exercise data were obtained from NH racehorses at 14 training yards. Canter, gallop and race distances accumulated in the 30 days preceding a 'case race' were calculated. Associations between exercise-, horse- and race-level variables and the odds of winning, winning prize money, being pulled up and falling were identified using mixed effects logistic regression.

RESULTS

Data from 4444 races run by 858 horses were included in analyses. Horses accumulating longer canter distances in the preceding 30 days were more likely to win or win prize money and less likely to be pulled-up. Horses accumulating longer race distances in a 30 day period were more likely to win, whilst those accumulating longer gallop distances in a 30 day period were more likely to win prize money. Horses that had jump-schooled in the preceding 30 days were more likely to fall during the race than those that had not. Trainer and horse were associated with racing performance after adjusting for exercise.

CONCLUSIONS

Results from this study suggest that NH race performance may be improved through modification of exercise regimens. After controlling for the abilities of individual trainers and horses and conditions of the case race, horses accumulating longer exercise distances in the 30 days preceding a race were more likely to be successful. However, horses that had jump-schooled in the 30 days preceding a race were more likely to fall.

Evaluation of selective and nonselective media for isolation of Helicobacter pylori from gastric biopsy specimens

The aim of the present study was to compare six media, three selective and three nonselective media, to determine the best combination of media for the primary isolation of Helicobacter pylori. Over a period of 8 months, mucosal antral biopsy specimens were obtained from 97 dyspeptic patients undergoing endoscopy. Biopsy samples were plated in parallel on all six media. Egg yolk emulsion agar (EYE), Skirrow's medium and modified Thayer-Martin medium were used as selective media; modified chocolate agar (MCHOC), Triptycase Soy Agar (TSA) and brain heart infusion agar were used as nonselective media. Overall, by using these six media, H. pylori were recovered from biopsy specimens from 48 of 97 patients, yielding an isolation rate of 49%. Comparison of all possible combinations of the six media showed that the highest rate of isolation of H. pylori was 100% (48 of 48) with EYE-MCHOC, followed by 97% (47 of 48) when EYE-SK was used. Conversely, it was found that none of the media used alone yielded a 100% rate of recovery (the maximum recovery rate was 92%, which was achieved with EYE). These results indicate that the association of EYE and MCHOC yielded the maximum recovery of H. pylori from gastric biopsy specimens. Therefore, the use of selective and nonselective media in parallel offers optimal recovery rates with only a slight increase in costs.

Plasma lactate and uric acid responses to racing in pacing Standardbreds and relationships with performance

Relationships between racing performance and plasma lactate and uric acid concentrations after racing were investigated in pacing Standardbred racehorses. The study was undertaken in order to better understand factors that limit racing performance. Twenty horses were tested after races of 1760 m and 28 horses after races over 2160 m. Blood samples were taken 30-60 min before and 8 and 30 min after a race. There were no significant differences between the race distances for prerace and 8 min postrace plasma lactates. Significant low correlations were obtained for plasma lactate concentration 8 min postrace and the number of race wins (r = 0.29, P = 0.04), number of race placings (1st, 2nd or 3rd; r = 0.34, P = 0.02) and lifetime earnings (r = 0.29, P = 0.04). Net lactate was correlated with the number of race placings (r = 0.31, P = 0.03). There were no significant correlations between performance indices and plasma uric acid concentrations in races of 1760 m. For races over 2160 m, correlations were found between plasma uric acid concentration at 8 min postrace and the number of race wins (r = 0.37, P = 0.06, 95% confidence limits 0-0.65). As well, there was a significant correlation between uric acid concentration at 8 min postrace and lifetime earnings (r = 0.35, P = 0.07, 95% confidence limits 0.06-0.64). Only 10-15% of the variability in retrospective career performance in pacing Standardbreds can be explained by these metabolic markers of the muscle anaerobic response to racing. Plasma lactate and uric acid responses to maximal exercise are unlikely to be useful for evaluating racing performance in pacing Standardbreds in univariate analysis.

Temporal changes in the trot between the first and third horse inspections at a CCI*** 3-day event

Kinematic parameters were measured from horses competing in a CCI*** 3-day event. The horses were filmed during the first and third horse inspection. This provided a repeat sample on 16 horses. The horses were filmed using a panning lateral S-VHS video camera (50 Hz). Spatial measurements were taken for mean +/- s.d. 5.66 +/- 0.92 strides for the first inspection and 5.05 +/- 1.27 for the third inspection. Within the calibration zone, data of the horses accelerating and obtaining a constant velocity were collected. The horses trotted with a higher mean velocity during the third inspection (0.26 +/- 0.05 m/s, P < 0.001). During the third inspection the horses trotted with a shorter stride length (0.193 +/- 0.03 m, P < 0.001) and stride duration (31 +/- 42 m/s, P < 0.001). The third inspection was characterised by a decrease in retraction percentage for both the forelimbs (3.69 +/- 2.39%, P < 0.001) and the hindlimbs (2.48 +/- 2.16%, P < 0.001). However, no significant difference was found between the 2 inspections for other temporal parameters when measured as a percentage of stride. It is proposed that the event horses trot with a decreased stride length and duration during the third horse inspection but maintain a consistent temporal relationship.

Cardiovascular and metabolic adaptations in horses competing in cross-country events

The cardiovascular and metabolic response to two cross-country events (CC*: preliminary level and CC*** advanced level) were analysed in 8 male eventing horses (4 Anglo-Hunter and 4 Anglo-Arabian). This study focused on the establishment of the main metabolic pathways involved in the muscle energy resynthesis during the competitions. Heart rate (HR) was recorded throughout the CC events. Jugular venous blood samples were withdrawn before the warm-up period, immediately after the competitions and at 5 and 10 min in the recuperation period. The following haematological parameters were studied: red blood cells (RBC), packed cell volume (PCV), haemoglobin concentration (Hb), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), white blood cells (WBC), and number and percentages of lymphocytes (LYM) and granulocytes and monocytes (GRAN). One fraction of blood was centrifuged and, in plasma, lactate (LA), total plasma protein (TPP) and the rate of LA disappearance were determined. The competitions induced significant increases in RBC, Hb, PCV, MCV and TPP. Plasma LA response exceeded the anaerobic threshold of 4 mmol/l, reaching a maximum level of 13.3 mmol/l. HR ranged from 140 to more than 200 bpm, peaking at 230 bpm, revealing a limitation in the oxygen supply to the working muscles. It was concluded that muscle energy resynthesis during a CC event is provided both through oxidative processes and glycolysis with LA formation. Therefore, both stamina and power exercises are required for eventing horses.

Energy sources and requirements of the exercising horse

This review outlines the energy sources available to the horse, from its diet and from its body stores, at rest and while exercising. It looks at the current ways of describing the energy potential of diets fed to horses and discusses the relative advantages and disadvantages of the digestible energy and net energy systems. The more empirical net energy system for calculating the energy available for maintenance and work is compared with a more physiological partitioning system. Finally, the energy requirements for maintenance and exercise are discussed, together with how they may be practically determined and achieved through different diets.

Exercise intolerance in endurance horses

Endurance competition requires synchronism and development of metabolic and musculoskeletal systems. An understanding of the existence of performance-limiting factors may permit the detection of exercise intolerance that could lead to performance failure, fatigue, and exhaustion. New concepts for assessment of fitness have increased the understanding of individual capacities and deficiencies and the interaction of the different systems involved in exercise.

Effects of transport and racing on ionic changes in thoroughbred race horses

1. Packed cell volume (PCV), blood glucose, total plasma proteins (TPP) and plasma electrolytes, osmolality, cortisol and aldosterone alterations produced by transport and racing, were investigated in race horses. 2. Plasma cortisol, sodium and blood glucose, found after transport, were higher, while aldosterone was lower than control levels. 3. After racing, PCV, blood glucose, TPP and plasma cortisol, sodium and osmolality were higher than control, while chloride diminished and aldosterone returned to control values. 4. These results demonstrate that transport and racing are different kinds of stressors, suggesting that the sympathetic system and hypophysis-suprarenal cortex axis have a dissimilar contribution to the physiological response.

A field study of post-exercise values of blood biochemical constituents in jumping horses: relationship with score, individual and event

The variability of the post-exercise values (PEV) of blood lactate and of some other blood constituents were studied in 8 healthy and fit jumpers through 5 national competitions of equal difficulty. The effects of factors such as the individual, performance and competition on these PEV were analysed. Venous blood was sampled immediately after the 5 show-jumping contests and was analysed for packed cell volume (PCV), blood lactate, blood glucose (GLU), total plasma protein (TPP), bicarbonate (HCO3-), sodium (Na+), potassium (K+), chloride (Cl-), calcium (Ca2+), serum activities of lactate dehydrogenase (LDH), creatine phosphokinase (CPK), glutamic-oxalacetic transminase (GOT) and gamma glutamyl transferase (gamma GT). PEV of these 13 blood parameters were analysed using a fixed linear model which included the effect of horse, score and competition and their respective interactions. The analysis of the influence of each of the 3 fixed variables showed that (1) there was no relationship between the PEV variations and the score; (2) there were significant (P less than 0.05) variations induced by the competition in Na+, Ca2+, TPP, LDH and GLU, and (3) there were significant interindividual variations as regards Ca2+, TPP, CPK, gamma GT and PCV with P less than 0.05, LDH with P less than 0.01 and blood lactate with P less than 0.001.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise-induced transient hyperlipidemia in the racehorse

Effects of graded intensity exercise on plasma lipids was studied in Standardbred and Finnishbred Trotters. The rate of lipolysis indicated by the elevated plasma concentrations of glycerol increased parallel with the intensity of the trot in the Standardbreds, but not as clearly in the Finnishbred trotters. During the exercise plasma triglyceride concentration increased significantly and the increase correlated with the intensity of the exercise as well as the activity of lipolysis. Together with the increase in plasma triglycerides, there was a parallel increase in the pre-beta fraction of lipoproteins which suggests that the hepatic synthesis of triglycerides was increased. It was calculated that about one third of the nonesterified fatty acids released in lipolysis during the high-intensity exercise is oxidized and the remainder is used for resynthesis of triglycerides. Since there were interstrain differences in the concentrations of triglycerides and glycerol after the high-intensity exercise it is suggested that the differences may be of some value in the estimation of recovery after submaximal exercise.

Circulatory, respiratory and metabolic responses in Thoroughbred horses during the first 400 meters of exercise

These studies investigated circulatory, respiratory and metabolic responses in four Thoroughbred geldings during the first 400 metres of galloping (mean speed 14.4 +/- 0.38 m.s-1), cantering (mean speed 10.0 +/- 0.61 m.s-1) and walking (mean speed 1.58 +/- 0.05 m.s-1) from a standing start. A radio-controlled device which collected blood samples anaerobically during each 100 m section of the exercise track allowed analyses of changes in and functional relationships of the variables measured. During the 400 m gallop, the mean heart rate (HR) increased from 125 to 201 beats.min-1 and the haematocrit (Hct) from 0.513 to 0.589 l/l-1. The haemoglobin [Hb], lactate [LA] and potassium [K+] concentrations increased significantly, while the pH and the partial pressure of oxygen (PaO2) decreased significantly. The arterial partial pressure of carbon dioxide (PaCO2) and the plasma bicarbonate concentration did not change significantly. There were significant correlations between HR and Hct, HR and [Hb], HR and PaO2, HR and pH, HR and PvCO2, HR and [LA], HR and [K+], pH and [K+], Hct and PaO2, [Hb] and PaO2, PaCO2 and PaO2, [LA] and PaO2, pH and PaO2, [K+] and PaO2, stride frequency and PaO2. With the exception of the PvCO2 which increased significantly, changes in venous blood during the gallop were in the same direction as those of arterial blood. Thirty seconds before the start of the gallop, both HR and [Hb] were significantly higher than at rest, providing an approximate three-fold increase in oxygen delivery compared to that of the resting state.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuroendocrine changes produced by competition stress on the Thoroughbred race horse

1. Packed cell volume (PCV) and plasma catecholamines, cortisol and glucose were determined in blood samples obtained from race horses, after competition. 2. All these parameters were higher than basals but catecholamines increased 6-7 times while cortisol was enhanced only by 25%. 3. The increase of glucose and PCV was related to the rise of catecholamines. 4. In samples withdrawn after overnight stress caused by change of horseshoes, it was not possible to find values from basal values significantly different. 5. Influence of nervous temperament was observed only in the higher hematocrit found in basal conditions, particularly in females.

Exercise testing

In the athletic horse, an exercise test may be required to measure the adaptation of the animal to a specific training program; to modify the training program in response to the progress achieved; to investigate the reasons for failure to perform at the expected level; and to form part of an overall clinical examination of a horse with a specific disability. This article includes information on the scope and form of an exercise test, the parameters measured during the test and their interpretation, treadmill and track tests, and the clinical applications of exercise tests.

Energy considerations during exercise

Maintenance of muscular contraction during exercise requires large amounts of chemical energy. Although various sources of energy are available, adenosine triphosphate (ATP) is the universal intracellular vehicle of chemical energy within skeletal muscle. This article will focus on the various mechanisms of the production and breakdown of ATP.

Cardiovascular response to exercise and training in the horse

The quality of the overall response to exercise in the horse is very similar to that seen in man and laboratory animals; differences are mainly quantitative and persist when relative body weight is taken into account. The apparently greater flow capacity of the equine muscle bed during maximal whole-body exercise implicates the extent of central circulatory adaptations as the limiting factor in performance but implies a role for increase in arteriolar capacitance/muscle capillarity as an appropriate response to intense endurance training. The blood oxygen-carrying capacity of the horse is often quoted as the major component of the animal's superior aerobic work capacity, although the measured maximal a-vO2 for the horse is only 2 to 3 ml greater than that found in elite athletes. In fact, comparison of published performance data for man and the horse reveals that improved a-vO2 accounts for 23 per cent of the difference, and increased Qc accounts for the remaining 77 per cent of the superior oxygen consumption in the horse. The extent to which the horse can increase Qc and muscle blood flow appears to represent its major adaptations for maximal aerobic performance. It is frequently observed that there have been far greater improvements in human athletic performance than in that of the race-horse, and this difference is usually attributed to the application of scientific training methods to the athlete. It has also been suggested that the horse may have reached the limit of its adaptive ability. The horse has a maximal oxygen pulse of at least 0.6 ml per kg per beat compared with 0.35 for man, a 90 per cent whole body oxygen extraction, and an 80 to 90 per cent higher muscle blood flow, with an overall capability of increasing Vo2 max by 35 times. These represent levels that would appear to be difficult to improve upon. However, insufficient research has been performed to firmly state true maxima for the horse, and current research does not reveal to what extent the horse is capable of responding to even conventional training methods. The relative improvement that such research could reveal would provide some objective guidance to the extent to which further improvement could be anticipated. A consistent finding in the majority of studies reviewed is the tendency for results to show a lack of statistical significance, which is particularly frustrating for a researcher when the trends are consistent with the initial hypotheses. This tendency arises because of small group sizes and inherent variability in the test population.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of a submaximal treadmill training programme on histochemical properties, enzyme activities and glycogen utilisation of skeletal muscle in the horse

The effects of training on skeletal muscle composition were studied in four Standardbred geldings given a seven week submaximal treadmill training programme. Before the start of training, muscle biopsies were collected from the left middle gluteal muscle for the determination of muscle fibre types, oxidative capacity and capillary numbers using histochemical techniques. The concentrations of citrate synthase, 3-hydroxyacyl-CoA dehydrogenase (HAD), lactate dehydrogenase and total muscle glycogen were measured using fluorometric methods. Muscle biopsy samples were repeated after one, three, five and seven weeks of training and the same measurements performed. No significant changes were found in muscle fibre types or capillary numbers as a result of training, although there was an increase in the oxidative capacity of the Type IIB fibres after seven weeks training. After seven weeks of training there were also increases in the concentrations of citrate synthase and HAD and a decrease in lactate dehydrogenase. Before commencement of training the horses underwent a standardised submaximal exercise test and muscle glycogen concentrations were measured before and immediately after the exercise. This procedure was repeated after one, three, five and seven weeks of training. A progressive decrease in the rate of glycogen utilisation occurred throughout the period of training, which by seven weeks was 36 per cent lower than that before training.