Prevalence, risk factors and genetic parameters of cresty neck in Pura Raza Español horses.

REASONS FOR PERFORMING STUDY: Cresty neck is a relatively common morphological defect in Pura Raza Español horses and other Baroque type horse breeds, which adversely affects the breeding industry. OBJECTIVES: To establish the within-breed prevalence, possible associated factors and heritability of cresty neck in Pura Raza Español horses. STUDY DESIGN: Cross-sectional analysis of a large worldwide database of Pura Raza Español horses. METHODS: The database included evaluations of 10,929 Pura Raza Español horses from 24 countries. Cresty neck score, on a 9 point scale, girth-to-height ratio, height at the withers, length of neck, head-neck junction and neck-body junction were recorded. A Bayesian genetic animal model included the following systematic effects: girth-to-height ratio, age, sex, coat colour and geographical area of the stud. Animal and residual effects were included as random effects. RESULTS: Within this Pura Raza Español population, 8.91% had a cresty neck score ≥5, which is the threshold for penalty or disqualification in the studbook of the breed. The age, sex, coat colour and stud geographical area were significantly associated with cresty neck score. The estimated heritability coefficient for cresty neck score was 0.37 (s.d. = 0.034) and genetic correlation between cresty neck score and other conformational traits ranged from -0.06 (height-at-withers) to -0.21 (neck-body junction). CONCLUSIONS: Cresty neck is a prevalent defect in Pura Raza Español horses, associated with age, sex, coat colour and other conformational traits, with a moderate level of heritability. Breeding to select against this condition may therefore be beneficial in this breed.

Eosinophilic Enteritis in Horses with Motor Neuron Disease.

BACKGROUND: Equine motor neuron disease (EMND) is a neuromuscular disorder that affects adult horses. Although EMND has been linked to vitamin E deficiency, its etiopathogenesis is poorly understood. OBJECTIVES: To describe clinical features, laboratory results, and postmortem findings in a series of young horses with motor neuron disease (MND). ANIMALS: A herd of 15 young Andalusian horses with weakness, weight loss, muscle atrophy, and muscle fasciculations related to restricted intake of green forage. METHODS: A case series is presented in which horses were subjected to a clinical examination and plasma vitamin E measurement. Five severely affected horses were euthanized for detailed postmortem examination. Muscle specimens were taken from the M. sacrocaudalis dorsalis medialis and the M. gluteus medius for histopathologic and morphometric evaluation. RESULTS: MND was diagnosed in 5 horses based on clinical signs, low serum levels of vitamin E (0.11 ± 0.05 mg/dL; normal range,: 0.3-1.5 mg/dL), changes in muscle histopathology (neurogenic atrophy), and spinal cord lesions (neuronal chromatolysis in ventral horns). An unexpected postmortem finding was the presence of intestinal inflammation (catarrhal enteritis, edema, and eosinophilic infiltrate) associated with the presence of giant ciliated protozoa in all of the horses. CONCLUSIONS: Although a mechanistic link could not be established, it is hypothesized that intestinal inflammation may have been involved in the decreased absorption of vitamin E, thus favoring the development of MND.

Effect of different blood-guided conditioning programmes on skeletal muscle ultrastructure and histochemistry of sport horses.

The effects of three different blood-guided conditioning programmes on ultrastructural and histochemical features of the gluteus medius muscle of 2-year-old sport horses were examined. Six non-trained Haflinger horses performed three consecutive conditioning programmes of varying lactate-guided intensities [velocities eliciting blood lactate concentrations of 1.5 (v1.5 ), 2.5 (v2.5 ) and 4 (v4 ) mm respectively] and durations (25 and 45 min). Each conditioning programme lasted 6 weeks and was followed by a 5-week resting period. Pre-, post- and deconditioning muscle biopsies were analysed. Although training and detraining adaptations were similar in nature, they varied significantly in magnitude among the three different conditioning programmes. Overall, the adaptations consisted in significant increases in size of mitochondria and myofibrils, as well as a hypertrophy of myofibrillar ATPase type IIA muscle fibres and a reduction in number of type IIx low-oxidative fibres. Together, these changes are compatible with a significant improvement in both muscle aerobic capacity and muscle strength. The use of v1.5 and v2.5 as the exercise intensities for 45 min elicited more significant adaptations in muscle, whereas conditioning horses at v4 for 25 min evoked minimal changes. Most of these muscular adaptations returned towards the pre-conditioning status after 5 weeks of inactivity. It is concluded that exercises of low or moderate intensities (in the range between v1.5 and v2.5 ) and long duration (45 min) are more effective for improving muscle features associated with stamina and power in sport horses than exercises of higher intensity (equivalent to v4 ) and shorter duration (25 min).

Unexplained underperformance syndrome in sport horses: classification, potential causes and recognition.

When inadequate training stress is applied and recovery time is insufficient, performance reduction and chronic maladaptation occurs. Known as overtraining syndrome (OTS), this complex condition afflicts horses in top training. The name of the syndrome implies causation and it is necessary to differentiate it from over-reaching, a term used in horses that, after suffering a loss of performance without an obvious clinical reason, recover their performance within 1 or 2 weeks. The term OTS should be used for horses in heavy training losing performance without an obvious clinical reason and which is sustained for > 2 weeks. Despite considerable scientific investigations, the underlying mechanisms are still poorly understood and there are no objective biomarkers for OTS. An imbalance between training and recovery seems to be the primary cause of this dysfunction. However, other factors such as transport, feeding, subclinical disease and general management may play a role. There is now sufficient evidence that red cell hypervolaemia is not a mechanism for the OTS in horses. A dysfunction of the hypothalamo-pituitary-adrenocortical axis is momentarily the only mechanism that may be related to the development of this syndrome. In the absence of a scoring system to assess the psychological status of horses, the most effective method for diagnosis is the thorough assessment of the history and presenting complaint (length of unexplained performance deficit, weight loss despite adequate feed intake, concurrence of unspecific subclinical problems, unsuccessful treatments and changes of behaviour). Standardised exercise tests are suggested to provide a way to detect subtle changes in hormonal responses in the individual, which may make an important contribution to the detection of early overtraining. But further longitudinal studies are needed to clarify mechanism(s) underlying OTS and to establish the potential for the use of a physiological test as a predictive tool of this disorder.

A scientific background for skeletal muscle conditioning in equine practice.

The main goal of any conditioning programme in athletic horses is to improve performance by inducing physiological changes within the animal's body. Equine skeletal muscles have a considerable potential to adapt during training and these adaptations have important physiological implications that influence stamina, strength and speed. Although there is an extensive specialized literature in this regard, scientific based muscle conditioning methods have not been introduced sufficiently in the equine sport practice. After a brief synopsis of both equine muscle exercise physiology and muscular adaptations to training, including their physiological significance, this review focuses on specific training programmes that induce muscular adaptations in athletic horses. The article addresses the following principal question: what kind of stimuli for what kind of muscular adaptations? The experimental data are discussed separately for racehorses (thoroughbreds, trotters and endurance horses) and sport horses (dressage, show jumpers and carriage). Finally, published results about the influence of relevant training parameters (such as intensity, duration and type of exercise) on muscular responses are discussed, as well as those concerning overtraining and detraining. The article closes with some concluding remarks on importance of their application in practice.

Oral L-carnitine combined with training promotes changes in skeletal muscle.

The purpose of this study was to determine whether oral L-carnitine supplementation enhances the responses of skeletal muscle to training in seven 2-year-old Standardbreds. Four horses were supplemented with 10 g/day L-carnitine for 10 weeks and 3 horses served as controls. All horses were exercised regularly every second day on a treadmill for 5 weeks (training period) and housed in individual boxes for 5 additional weeks (detraining period). The training period consisted of 8 high- and 8 low-speed exercises carried out in alternating sequence. Gluteus medius muscle biopsies were taken at Weeks 0 (pretraining), 5 (post-training) and 10 (detraining). Muscular adaptations to training were observed mainly in the L-carnitine-supplemented horses and included an increase in the percentage of type IIA fibres (delta35%, P<0.05), atrophy of type I fibres (delta24%, P<0.01), a rise in the capillary-to-fibre ratio (delta40%, P<0.01) and an increase in the quantitative reaction of periodic acid Schiff stain (delta11%, P<0.05), used as an indicator of intrafibre glycogen content. After detraining, most of these adaptations reverted towards the pretraining situation. Therefore, exogenous carnitine has an additive effect on muscular responses to training and this should be favourable to improve athletic performance. Nevertheless, further studies are necessary to show whether muscle carnitine content is a limiting factor for fatty acid oxidation.

Early evaluation of dressage ability in different breeds.

Dressage is one of the Olympic equestrian sports practiced in several countries using different horse breeds. Specific characteristics of the walk, trot and canter are required for dressage. It has been assumed that some of these traits could be selected for genetically and contribute to dressage performance. The purpose of this study was to compare the walk, trot and conformation characteristics in young horses of different breeds used for dressage. A total of 142 horses age 3 years were classified into 3 groups of breeds (German, French and Spanish saddle horses) and tested using the same procedure. The skeletal conformation measurements were made by image analysis. Gait variables of the walk and trot were measured by the accelerometric gait analysis system Equimetrix. Discriminant analysis could explain the variability between the groups by taking into account the walk (P<0.0003), trot (P<0.0001) and conformation variables (P<0.0001). Many gait and conformation variables were significantly different between the breeds. In summary, the German horses had gait characteristics more adapted for dressage competition, and the results of this group could be used as a reference for early evaluation in dressage. Purebred Spanish horses could be considered as a reference for collected gaits used for farm work and old academic dressage. The gait and conformation tests could be applied in a breeding or crossing plan to detect more accurately young horses with good dressage ability.

Effects of transcutaneous short-term electrical stimulation on M. vastus lateralis characteristics of healthy young men.

Fifteen healthy, untrained male subjects (mean age +/- SD, 22 +/- 5 years) were used to examine the plasticity of myosin heavy chain phenotype, size, oxidative capacity and capillarization of skeletal muscle fibre types with short-term electrical stimulation (ES). Ten subjects were electro-stimulated on both quadriceps muscles with a frequency of 45-60 Hz, with 12 s of stimulation followed by 8 s of recovery for a total of 30 min per day, 3 days per week for 6 weeks. The remaining five subjects served as controls. Two vastus lateralis muscle biopsy samples were removed from each subject before (week 0) and after (week 6) ES training. A standardized exercise test on a cycle ergometer was performed by each subject before and after the experimental period and several indicators of whole-body aerobic capacity were estimated. The so-called electromyographic threshold was also determined during the tests. Muscle biopsy samples were analysed by electrophoresis, immunohistochemistry and quantitative histochemistry. Myosin heavy chain (MHC) composition, muscle fibre type distribution, fibre areas, oxidative capacity and capillaries of each fibre type were estimated. Muscular changes with ES revealed an increase of fibres expressing MHC-IIA, and a decrease of fibres expressing MHC-IIX and MHC-I, as well as an increase of the oxidative capacity and mean number of capillaries of fast-twitch (type II) fibres with minimal muscle fibre hypertrophy. These adaptations seem related to a bi-directional transformation from both MHC isoforms I and IIX towards the MHC-IIA isoform. The aerobic performance and electromyographic variables at the whole-body level were not altered by ES. These results indicate that the particular short-term ES training protocol tested in the present study induces significant adaptations in histochemical and metabolic machineries of human skeletal muscle. The results also offer new perspectives for realistic applications of ES in various clinical situations and sport training.

Polysaccharide storage myopathy in the M. longissimus lumborum of showjumpers and dressage horses with back pain.

This study was designed to investigate whether horses with clinical signs of back pain due to suspected soft tissue injuries were affected by polysaccharide storage myopathy (PSSM). Diagnosis of PSSM in muscle biopsies obtained from the M. longissimus lumborum of 5 showjumpers and 4 dressage horses with a history of back pain is reported. M. longissimus lumborum biopsies of these horses were characterised histopathologically and in 3/9 cases also by electron microscopy. Observations were compared with M. gluteus biopsies of the same horses, and with M. gluteus biopsies obtained from 6 Standardbreds with recurrent exertional rhabdomyolysis and from 6 healthy trotters. M. longissimus biopsies from horses with back pain showed pathognomonic signs of PSSM, i.e. high glycogen and/or abnormal complex amylase-resistant polysaccharide deposits. Similar features were found in M. gluteus biopsies of the same horses. Sections of horses with rhabdomyolysis had increased PAS stain when compared with healthy horses, but did not show amylase-resistant material. Qualitative observations were corroborated by quantitative histochemistry (optical densities) of sections stained with PAS and amylase PAS. This study demonstrated the presence of PSSM in the M. longissimus of showjumpers and dressage horses with back pain and indicates that epaxial muscle biopsy is an option in diagnosing back problems in horses when clinical examination and imaging techniques do not provide a precise diagnosis.