Exertional heat illness in Thoroughbred racehorses – Pathophysiology,case definition and treatment rationale

The combination of extreme heat, humidity and strenuous exercise is potentially challenging to the thermoregulatory system of a Thoroughbred racehorse, and under certain circumstances can cause a condition called exertional heat illness (EHI). It is difficult to predict its occurrence in an individual animal due to the combination on race day of extrinsic and intrinsic risk factors. Education regarding EHI is essential to its prevention, and lack of understanding amongst those responsible for the horse’s care may in fact be the most important risk factor. The pathophysiology of EHI is similar across elite athletic species and is directly related to an elevation in core body temperature that exceeds the ‘critical thermal maximum’, causing widespread destruction of cells. It is not only the high core temperature but also its duration that will dictate outcome. Treatment strategies should decrease the hyperthermia to near normal levels within 30 min of onset, which will minimise adverse consequences. This review article outlines the pathophysiological changes as EHI progresses, and the case definition at each emergent level. Pharmacological treatment strategies and their rationale are presented. Aggressive cooling, however, is the key treatment and requires a technique which is both practical and effective in rapidly reducing core body temperature. The treatment paradigm is early detection, rapid assessment enabling prioritisation of individuals and aggressive cooling. Each stage is critically discussed.     

Influence of different exercise regimes on the proximal hoof circumference in young Thoroughbred horses

Reasons for performing study: Most lameness in horses relates to foot problems and may be associated with changes in hoof shape, but there is a lack of information on the influence of normal exercise on hoof shape. Objectives: To investigate the effect of training on proximal hoof circumference in young Thoroughbred racehorses being prepared for racing. Methods: Thirty‐seven young Thoroughbred racehorses were included in this study. Front hoof circumference immediately below the coronary band was measured weekly with a measuring tape in all horses present at the stable. Most horses accomplished a minimum of 2 training periods at the stable separated by periods of rest on a paddock. One sample t tests were used to evaluate if the mean change per week differed from zero. To estimate the repeatability coefficient, the left proximal hoof circumference of 25 horses was measured 3 times in a random order on one day. Results: Most horses showed a similar pattern of change. The proximal hoof circumference decreased during the training periods (P<0.0001) and increased when the horse was rested (P<0.0001). The decrease of the circumference during the first training period was ?0.66 mm/week on the left and ?0.64 mm/week on the right. During the second training period, this was ?0.58 mm/week on the left and ?0.57 mm/week on the right. During the rest period, the circumference increased by 1.03 mm/week on the left and 1.12 mm/week on the right. The repeatability coefficient for the left circumference was 1.8 mm. Conclusions: Horses showed a decrease in circumference during race training that reversed when they were rested. Potential relevance: Measurement of front hoof circumference is a simple method to assess change in hoof shape. It provides an opportunity to investigate the relationships between specific training, hoof shape and soundness.     

Particle mapping in stables at an American Thoroughbred racetrack

Reasons for performing study: Airway inflammation and mucus in the trachea are common in racehorses. Fine airborne particles can initiate and coarse particles can worsen airway inflammation in man and in animal models of airway disease. The regional and seasonal distribution of particles of different sizes has never been investigated in American racing stables. Objectives: To determine the regional and seasonal concentration and number of airborne particles of different sizes in racing stables. Methods: Direct reading instruments were used to determine the mass concentration and numbers of particles 3 times daily (early morning, midday and late afternoon) in July, September and November, in 3 different racing stables. Results: Average particle concentrations were lowest in July and highest in September and November. Early morning concentrations were significantly higher than those measured throughout the rest of the day. The completely enclosed stable with little natural ventilation, had significantly higher particulate concentrations than the open‐sided stable. With regard to numbers of particles, those 2–5 µm were greatest in July and least in November; those 0.5–1.0 µm were greatest in September and least in November. Location of stall within stable also affected concentrations and numbers. Conclusions: The concentration and number of particles in sizes known to reach the lower airways varies with stable design/management, time of day, season of year and location of the stall within the stable. Potential relevance: Particle mapping is a useful tool in the identification of stables, season, and location of stalls within stables where horses may be at greater risk of exposure to offending particulates.     

Sudden death in racing Thoroughbred horses: an international multicentre study of post mortem findings

Reasons for performing study: To improve the understanding of exercise related sudden death in Thoroughbred racehorses. Objectives: To describe the post mortem findings in cases of sudden death associated with exercise in 268 Thoroughbred racehorses. Methods: Gross and histological post mortem findings of 268 cases of sudden death were collated and reviewed. Cases originated from 6 racing jurisdictions around the world. Sudden death was defined as acute collapse and death in a closely observed and previously apparently healthy Thoroughbred racehorse, during, or within one hour after, exercise. Cause of death as determined by the attending pathologist was categorised as definitive, presumptive or unexplained and compared between the different populations. Cardiopulmonary lesions recorded at post mortem examination were compared between different populations. Results: Pathologists recorded a definitive cause of death in 53% (143/268) of cases. Major definitive causes of sudden death included cardiac failure, apparent pulmonary failure, pulmonary haemorrhage, haemorrhage associated with pelvic fractures or with idiopathic blood vessel rupture, and spinal cord injury. A presumptive cause of death was made in 25% (67/268) of cases and death remained unexplained in 22% (58/268) of cases. There were several statistically significant inter‐population differences in the cause of death and in reporting of cardiopulmonary lesions. Conclusions: Sudden death can be attributed to a variety of causes. Causes of sudden death and the lesions found in cases of exercise‐related sudden death are similar in different racing jurisdictions. However, the lesions are often not specific for the cause of death and determination of the cause of death is therefore affected by interpretation by the individual pathologist.     

An epidemiological study of myopathies in Warmblood horses

REASON FOR PERFORMING STUDY: There are few detailed reports describing muscular disorders in Warmblood horses. OBJECTIVES: To determine the types of muscular disorders that occur in Warmblood horses, along with presenting clinical signs, associated risk factors and response to diet and exercise recommendations, and to compare these characteristics between horses diagnosed with polysaccharide storage myopathy (PSSM), those diagnosed with a neuromuscular disorder other than PSSM (non-PSSM) and control horses. METHODS: Subject details, muscle biopsy diagnosis and clinical history were compiled for Warmblood horses identified from records of biopsy submissions to the University of Minnesota Neuromuscular Diagnostic Laboratory. A standardised questionnaire was answered by owners at least 6 months after receiving the muscle biopsy report for an affected and a control horse. RESULTS: Polysaccharide storage myopathy (72/132 horses) was the most common myopathy identified followed by recurrent exertional rhabdomyolysis (RER) (7/132), neurogenic or myogenic atrophy (7/132), and nonspecific myopathic changes (14/132). Thirty-two biopsies were normal. Gait abnormality, 'tying-up', Shivers, muscle fasciculations and atrophy were common presenting clinical signs. Forty-five owners completed questionnaires. There were no differences in sex, age, breed, history or management between control, PSSM and non-PSSM horses. Owners that provided the recommended low starch fat supplemented diet and regular daily exercise reported improvement in clinical signs in 68% (19/28) of horses with a biopsy submission and 71% of horses diagnosed with PSSM (15/21). CONCLUSIONS: Muscle biopsy evaluation was a valuable tool to identify a variety of myopathies in Warmblood breeds including PSSM and RER. These myopathies often presented as gait abnormalities or overt exertional rhabdomyolysis and both a low starch fat supplemented diet and regular exercise appeared to be important in their successful management. POTENTIAL RELEVANCE: Warmbloods are affected by a variety of muscle disorders, which, following muscle biopsy diagnosis can be improved through changes in diet and exercise regimes.     

相对湿度对家禽水蒸发散热和健康的影响

相对湿度(RH)作为温热环境的重要因素之一,与温度和风速等共同影响家禽的热平衡状态。当RH适宜时,蒸发散热(EHL)达到最大;高温环境下,高湿会阻碍家禽的EHL,从而造成体温上升、呼吸加快、食欲下降,严重时导致酸碱平衡紊乱、热虚脱和呼吸性碱中毒。本文主要综述水蒸发散热(EWL)在家禽热平衡调节中的重要作用,及RH对家禽EWL的影响,并结合由此而引发的对家禽健康的影响,探讨RH在家禽实际生产中的重要作用。     

Assessment of dynamic upper respiratory tract function in the equine athlete

Dynamic upper respiratory tract (URT) obstructions occur commonly in the equine athlete. During the past 25 years, veterinary diagnostic capabilities have improved greatly with the ability to perform endoscopy during exercise and thus to visualise upper airway function during various types of exercise. After correctly reproducing and diagnosing an URT obstruction, the veterinary surgeon must consider the functional significance of the endoscopic findings for that individual athlete. This is the third paper in this series and focuses on the diagnosis of URT obstructions, their relationship to the exercise test and their functional significance.     

Evaluation of a new strategy to modulate skeletal development in racehorses by imposing track-based exercise during growth: the effects on 2- and 3-year-old racing careers

REASON FOR PERFORMING STUDY: No data exist on the effects of conditioning exercise at foal age on workload and subsequent clinical injury rate during their 2- and 3-year-old racing careers. OBJECTIVES: To investigate the effects of subjecting TB foals to conditioning exercise prior to the start of race training on: the workload required to reach a level of fitness sufficient to compete; and the prevalence of orthopaedic injury during the first 2 seasons of their racing careers. METHODS: Twenty 18-month-old TBs, 12 subjected to conditioning exercise at foal age (CONDEX) and 8 exercised spontaneously at pasture only (PASTEX) were trained and entered in competitive events. Workload was quantified using the cumulative workload index (the product of average velocity and distance at a specific gait) and the animals were monitored clinically and radiographically for signs of musculoskeletal disorders. RESULTS: Workload to reach the desired fitness level was similar for CONDEX and PASTEX. CONDEX performed more prerace training sessions as 2-year-olds (P<0.05). The incidence of orthopaedic injuries was low in both groups and there were no differences in the occurrence of orthopaedic ailments. PASTEX animals tended to show signs of musculoskeletal disorders earlier than CONDEX animals. This time difference was significant for metacarpophalangeal joint pain on flexion, reduced carpal flexion and hindlimb lameness (P<0.05). CONCLUSIONS: Subjecting TB foals to conditioning exercise early in life does not have adverse effects on racing careers at ages 2 and 3 years, and does not influence the workload needed to reach a fitness level that is sufficient for racing. POTENTIAL RELEVANCE: The lack of negative effects and the indications of some positive effects of early conditioning exercise in the Thoroughbred encourage further large-scale comparative studies.