Post exercise changes in compartmental body temperature accompanying intermittent cold water cooling in the hyperthermic horse

Post-exercise management of exertional hyperthermia in dogs participating in dog sport (canicross) events in the UK

Exercise is a common trigger of heat-related illness (HRI) events in dogs, accounting for 74% of canine HRI cases treated under primary veterinary care in the United Kingdom. However, few empirical studies have evaluated the effectiveness of differing cooling methods for dogs with exertional hyperthermia or HRI. This study aimed to prospectively evaluate effects of ambient conditions and post-exercise management practices (cooling methods and vehicular confinement) on the post-exercise temperature change of dogs participating in UK canicross events. Canine temperature was recorded at three intervals post-exercise: as close as possible to 0- (immediately post-exercise), 5-, and 15-min post-exercise. Ambient conditions and post-exercise management were recorded for 115 cooling profiles from 52 dogs. In 28/115 (24.4%) profiles, the dog's temperature increased during the first 5-min post-exercise. Overall, 68/115 (59.1%) profiles included passive cooling (stood or walked outside), 35 (30.4%) active cooling (cold-water immersion or application of a cooling coat), and 12 (10.4%) involved no cooling and were immediately housed in vehicles. No dogs developed hypothermia during the study and no adverse effects were observed from any cooling method. In hyperthermic dogs, overall post-exercise body temperature change was significantly negatively associated (i.e. the dogs cooled more) with 0-min post-exercise body temperature (β = -0.93, p < 0.001), and not being housed in a vehicle (β = -0.43, p = 0.013). This study provides evidence cold-water immersion (in water at 0.1-15.0 °C) can be used to effectively and safely cool dogs with exertional hyperthermia. Progressive temperature increases in many dogs - even after exercise has terminated - supports the message to "cool first, transport second" when managing dogs with HRI. When transporting dogs post-exercise or with HRI even after active cooling, care should be taken to cool the vehicle before entry and promote air movement around the dog during transport to facilitate ongoing cooling and prevent worsening of hyperthermia during travel.

Impact of different cooling solutions on autonomic modulation in horses in a novice endurance ride

Cooling down is essential for horse recovery before veterinary inspection during an endurance ride. As salt potentially decreases water temperature, we tested whether adding salt to the water used to cool horses could aid their recovery. Twelve healthy Arabian horses participating in a novice endurance ride were divided evenly into two groups. Heart rate variability (HRV) variables, including time and frequency domains, non-linear results, and autonomic nervous system indices, were determined before recovery and at 1-min intervals for 9 min during recovery using either cold or cold-saline water. An interaction between water type and time was observed in the modulation of the SD of beat-to-beat (RR) intervals, square root of the mean squared differences between successive RR intervals (RMSSD), HRV triangular index, very low-frequency band (VLF), low-frequency band/high-frequency band ratio, and SD of the Poincaré plot perpendicular to the line of identity (SD1) non-linear results. A decrease in heart rate and the sympathetic nervous system index corresponding to an increase in RR intervals and the parasympathetic nervous system (PNS) index was observed over time. A rise in the triangular interpolation of the normal-to-normal intervals, number of successive RR interval pairs that differ more than 50 ms, low-frequency band, and total power, coinciding with decreased stress index, was detected at 9 min of recovery. A difference between RMSSD and SD1 was observed between groups, in which they were higher in horses cooling with cold-saline water when compared to cold water at 5 min after cooling began. An increase in VLF was seen at 9 min only in horses cooled with cold-saline water. In conclusion, different water types distinctly impacted HRV in horses. The predominant PNS activity in horses recovering with cold-saline water reflects its positive impact on cooling during an endurance ride.

Thermoregulation during Field Exercise in Horses Using Skin Temperature Monitoring

Hyperthermia and exertional heat illness (EHI) are performance and welfare issues for all exercising horses. Monitoring the thermoregulatory response allows for early recognition of metabolic heat accumulation during exercise and the possibility of taking prompt and effective preventative measures to avoid a further increase in core body temperature (Tc) leading to hyperthermia. Skin temperature (Tsk) monitoring is most used as a non-invasive tool to assess the thermoregulatory response pre- and post-exercise, particularly employing infrared thermographic equipment. However, only a few studies have used thermography to monitor skin temperature continuously during exercise. This commentary provides an overview of studies investigating surface skin temperature mainly by infrared thermography (IRT) during exercise. The scientific evidence, including methodologies, applications, and challenges associated with (continuous) skin temperature monitoring in horses during field exercise, is discussed. The commentary highlights that, while monitoring Tsk is straightforward, continuous Tsk alone does not always reliably estimate Tc evolvement during field exercise. In addition, inter-individual differences in thermoregulation need to be recognized and accounted for to optimize individual wellbeing. With the ongoing development and application of advanced wearable monitoring technology, there may be future advances in equipment and modeling for timely intervention with horses at hyperthermic risk to improve their welfare. However, at this point, infrared thermographic assessment of Tsk should always be used in conjunction with other clinical assessments and veterinary examinations for a reliable monitoring of the welfare of the horse.

Heat stress in horses: a literature review

Healthy adult horses can balance accumulation and dissipation of body heat to maintain their body temperature between 37.5 and 38.5 °C, when they are in their thermoneutral zone (5 to 25 °C). However, under some circumstances, such as following strenuous exercise under hot, or hot and humid conditions, the accumulation of body heat exceeds dissipation and horses can suffer from heat stress. Prolonged or severe heat stress can lead to anhidrosis, heat stroke, or brain damage in the horse. To ameliorate the negative effects of high heat load in the body, early detection of heat stress and immediate human intervention is required to reduce the horse's elevated body temperature in a timely manner. Body temperature measurement and deviations from the normal range are used to detect heat stress. Rectal temperature is the most commonly used method to monitor body temperature in horses, but other body temperature monitoring technologies, percutaneous thermal sensing microchips or infrared thermometry, are currently being studied for routine monitoring of the body temperature of horses as a more practical alternative. When heat stress is detected, horses can be cooled down by cool water application, air movement over the horse (e.g., fans), or a combination of these. The early detection of heat stress and the use of the most effective cooling methods is important to improve the welfare of heat stressed horses.

An Overview of Exertional Heat Illness in Thoroughbred Racehorses: Pathophysiology, Diagnosis, and Treatment Rationale

Exertional heat illness (EHI) is a complex medical disease. The thoroughbred (TB) racehorse is at considerable risk because of the intensity of its exercise activity and its high rate of metabolic heat production. The pathophysiology of EHI can combine aspects of both the heat toxicity pathway and the heat sepsis or endotoxemic pathway. Treatment regimes depend upon the detection of earliest clinical signs, rapid assessment, aggressive cooling and judicious use of ancillary medications. Ice-cold water provides the most rapid cooling, consistent with the need to lower core body temperature before tissue damage occurs. Research into EHI/HS by inducing the condition experimentally is ethically unjustifiable. Consequently, leading researchers in the human field have conceded that "most of our knowledge has been gained from anecdotal incidents, gathered from military personnel and athletes who have collapsed during or following physical activity, and that retrospective and case studies have provided important evidence regarding recognition and treatment of EHI". The authors' review into EHI shares that perspective, and the recommendations made herein are based on observations of heat-affected racehorses at the racetrack and their response, or lack of response, to treatment. From 2014 to 2018, 73 race meetings were attended, and of the 4809 individual starters, signs of EHI were recorded in 457. That observational study formed the basis for a series of articles which have been published under the title, 'EHI in Thoroughbred racehorses in eastern Australia', and forms the background for this review.

Evaluation of thermoregulation of horses (Equus caballus) submitted to two methods of post-exercise cooling, in hot and humid climate conditions, in the Eastern Amazon

In Brazil, the study on equine thermoregulation has not shown considerable advances, moreover, in the Amazon, this is a little explored aspect. This study aims to evaluate the thermoregulation of horses submitted to two methods of post-exercise cooling, in the climatic conditions of the Eastern Amazon. The experiment was conducted at Centro Hipico, Ananindeua, Para, for 15 days. Ten male horses, castrated of the Brazilian breed, aged 13 years and with an average weight of 482.3 kg were used. Equestrianism, which was exercised with pre-established protocol in the arena and track, for 30 min. After the exercise, the animals were divided into two groups for application of the treatments, which were two cooling methods, such as a bath with water at room temperature (about 25°C) and a hiper cooling method (6-9°C). During the experimental period, air temperature (AT) and relative humidity (RH) data were recorded and the Temperature and Humidity Index (THI) was calculated. Data from the rectal temperature (RT), heart rate (HR), respiratory rate (RR) and Body surface temperature (BST) of the animals were also measured at three moments: before exercise, after exercise and after applying the cooling methods. The adaptability index used was the Benezra Thermal Comfort Index (BTCI). The BST was performed with the help of infrared thermograph, which were the left side of the neck, thorax, rump, and right side to the armpi, before the exercise, after the exercise and after applying the cooling methods. The statistical design was completely randomized. Analysis of variance was performed using the GLM Procedure of SAS 9.1.3. After the application of the cooling techniques in the animals, the AT and THI were higher and the highest RH values were found before the exercise (87.21%). The highest RT, RR, HR, BST, and BTCI values were observed after exercise. There was no significant dierence (P > 0.05) between cooling methods. There was a highly significant and positive correlation (P < 0.01) between all physiological variables (RT, RR, HR, and BST) and the Iberian Index with AT and THI and negative with RH (P < 0.01), thus demonstrating the influence of the environment on the thermoregulation of animals. It is concluded the evaluation of stress, welfare and thermoregulation of horses submitted to two methods of post-exercise cooling, in the climatic conditions of the Eastern Amazon, demonstrated that the studied cooling methods showed to reduce the rectal temperature, the respiratory rate, the heart rate and the body surface temperature with equal efficiency. However, in terms of practical ease of use, the room temperature water cooling method has proven to be more practical.

Is Continuous Monitoring of Skin Surface Temperature a Reliable Proxy to Assess the Thermoregulatory Response in Endurance Horses During Field Exercise?

Hyperthermia is a performance and welfare issue for exercising horses. The thermoregulatory stressors associated with exercise have typically been estimated by responses in the laboratory. However, monitoring surface skin temperature (T_sk) coincident with core temperature (T_c) has not previously been investigated in horses exercising in the field. We investigated the suitability of monitoring surface T_sk as a metric of the thermoregulatory response, and simultaneously investigated its relationship with T_c using gastrointestinal (GI) temperature. We evaluated T_sk in 13 endurance horses competing during four endurance rides over 40 km (n = 1) or a total of 80 km (n = 12) distance. Following each 40-km loop, the horses were rested for 60 min. T_sk and T_c were continuously recorded every 15 s by an infrared thermistor sensor located in a modified belt and by telemetric GI pill, respectively, and expressed as mean ± SD. The net area under the curve (AUC) was calculated to estimate the thermoregulatory response to the thermal load of T_sk over time (°C × minutes) using the trapezoidal method. The relationship between T_sk and T_c was assessed using scatterplots, paired t-test or generalized linear model ANOVA (delta T_sk) (n = 8). Ambient temperature ranged from 6.7°C to 18.4°C. No relationship was found between T_sk and T_c profiles during exercise and recovery periods, and no significant difference between delta T_sk results was detected when comparing exercise and rest. However, time to maximum T_sk (67 min) was significantly reduced compared to T_c (139 min) (p = 0.0004) with a significantly lesser maximum T_sk (30.3°C) than T_c (39°C) (p = 0.0002) during exercise. Net AUC T_sk was 1,164 ± 1,448 and −305 ± 388°C × minutes during periods of exercise and recovery, respectively. We conclude that T_sk monitoring does not provide a reliable proxy for the thermoregulatory response and horse welfare, most probably because many factors can modulate T_sk without directly affecting T_c. Those factors, such as weather conditions, applicable to all field studies can influence the results of T_sk in endurance horses. The study also reveals important inter-individual differences in T_sk and T_c time profiles, emphasizing the importance of an individualized model of temperature monitoring.

The Use of Percutaneous Thermal Sensing Microchips to Measure Body Temperature in Horses during and after Exercise Using Three Different Cool-Down Methods

The frequent monitoring of a horse’s body temperature post strenuous exercise is critical to prevent or alleviate exertional heat illness (EHI) from occurring. Percutaneous thermal sensing microchip (PTSM) technology has the potential to be used as a means of monitoring a horse’s body temperature during and post-exercise. However, the accuracy of the temperature readings obtained, and their relationship to core body temperature are dependent on where they are implanted. This study aimed to document the relationship between core body temperature, and temperature readings obtained using PTSM implanted in different muscles, during exercise and post application of different cool-down methods. PTSMs were implanted into the right pectoral, right gluteal, right splenius muscles, and nuchal ligament. The temperatures were monitored during treadmill exercise, and post application of three different cool-down methods: no water application (Wno), water application only (Wonly), and water application following scraping (Wscraping). Central venous temperature (TCV) and PTSM temperatures from each region were obtained to investigate the optimal body site for microchip implantation. In this study, PTSM technology provided a practical, safe, and quick means of measuring body temperature in horses. However, its temperature readings varied depending on the implantation site. All muscle temperature readings exhibited strong relationships with TCV (r = 0.85~0.92, p < 0.05) after treadmill exercise without human intervention (water application), while the nuchal ligament temperature showed poor relationship with TCV. The relationships between TCV and PTSM temperatures became weaker with water application. Overall, however the pectoral muscle temperature measured by PTSM technology had the most constant relationships with TCV and showed the best potential to act as an alternate means of monitoring body temperature in horses for 50 min post-exercise, when there was no human intervention with cold water application.

Effect of Different Water Cooling Treatments on Changes in Rectal and Surface Body Temperature in Leisure Horses after Medium-Intensity Effort

Simple Summary

The study was performed in order to answer the question: should horses be cooled after not very intensive exercise? Thus, the efficiency of four different water cooling methods was studied in horses after medium-intensity effort for leisure horses under moderate air temperature. The water cooling methods used included spraying with cold water: (1) lower body parts, i.e., lower parts of legs; (2) upper body parts, i.e., back of the head and flanks; and (3) both lower and upper body parts. The control group was not treated with water. Water cooling was applied to 19 warmblood geldings immediately after the end of exercise and 10 and 20 min later. The internal and body surface temperatures were registered and analyzed. The water cooling methods used led to a decrease in rectal and body surface temperature. Applying cold water on lower body parts was only effective and can be recommended for practical use under the described conditions.

Abstract

Cooling a horse after intensive exercise under hot conditions is commonly recommended. The study aimed to analyze changes in the rectal and surface temperature of the horses subjected to various water cooling treatments. This followed medium-intensity exercise performed by leisure horses under moderate air temperature. The experiment involved a control group without water application, and three variants of water cooling applied to 19 warmblood geldings after medium-intensity effort. Cooling of lower, upper, and lower and upper body parts was performed. In each variant, the rectal and body surface temperatures were measured five times: before; immediately after; and 10, 20, and 30 min after effort. Using water cooling under the studied conditions did not influence a post-exercise decrease in the rectal temperature. The decrease in body surface temperature depended on the used variant of cooling down the horse. Cooling the limbs by pouring water several times changed the surface body temperature from 34.2 ± 0.37 °C to 32.0 ± 0.32 °C and was more efficient than the repeated application of cool water on both the upper and lower body parts, leading to a temperature change from 34.6 ± 0.26 °C to 33.2 ± 0.36 °C. Thus, the application of cold water on the limbs only is sufficient for cooling the horse after medium-intensity exercise under moderate air temperature (about 24 °C).

Effect of post-exercise muscle cooling on PGC-1α and VEGF mRNA expression in Thoroughbreds

Besides preventing exertional heat illness, muscle cooling can be a potential strategy to enhance exercise-training induced adaptations. This study aimed to examine the effects of post-exercise cooling on the mRNA expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and vascular endothelial growth factor (VEGF) in Thoroughbred skeletal muscle. Five Thoroughbred horses performed treadmill running until their pulmonary artery temperature reached 42 °C, followed by walking on the treadmill with no additional cooling (CONT) or muscle cooling with a shower using the tap water (26 °C, 0.4 l/s; COOL), for 30 min. Muscle biopsies were obtained before (PRE) and 3 h after exercise (3 Hr-REC) from the gluteus medius muscle. PGC-1α mRNA expression was elevated 3 h after exercise in both the CONT (PRE vs 3 Hr-REC: 1.0±0.1 vs 5.0±0.8, P<0.01) and COOL (PRE vs 3 Hr-REC: 1.1±0.3 vs 6.6±0.9, P<0.01) conditions; however, there was no difference between the two conditions at 3 h after exercise (P=0.17). VEGF mRNA expression was elevated 3 h after exercise in COOL (PRE vs 3 Hr-REC: 1.0±0.2 vs 2.2±0.2, P<0.05) but not in CONT (PRE vs 3 Hr-REC: 1.0±0.1 vs 1.8±0.3, P=0.08). VEGF mRNA expression at 3 h after exercise was significantly negatively correlated with rectal temperature at the end of the 30-min cooling period (r = -0.65, P<0.05). Our results suggest that the decline in body temperature after exercise may lead to greater expression of the key angiogenic gene in Thoroughbred horses.

Sarcoplasmic Reticulum from Horse Gluteal Muscle Is Poised for Enhanced Calcium Transport

We have analyzed the enzymatic activity of the sarcoplasmic reticulum (SR) Ca²⁺-transporting ATPase (SERCA) from the horse gluteal muscle. Horses are bred for peak athletic performance yet exhibit a high incidence of exertional rhabdomyolysis, with elevated levels of cytosolic Ca²⁺ proposed as a correlative linkage. We recently reported an improved protocol for isolating SR vesicles from horse muscle; these horse SR vesicles contain an abundant level of SERCA and only trace-levels of sarcolipin (SLN), the inhibitory peptide subunit of SERCA in mammalian fast-twitch skeletal muscle. Here, we report that the in vitro Ca²⁺ transport rate of horse SR vesicles is 2.3 ± 0.7-fold greater than rabbit SR vesicles, which express close to equimolar levels of SERCA and SLN. This suggests that horse myofibers exhibit an enhanced SR Ca²⁺ transport rate and increased luminal Ca²⁺ stores in vivo. Using the densitometry of Coomassie-stained SDS-PAGE gels, we determined that horse SR vesicles express an abundant level of the luminal SR Ca²⁺ storage protein calsequestrin (CASQ), with a CASQ-to-SERCA ratio about double that in rabbit SR vesicles. Thus, we propose that SR Ca²⁺ cycling in horse myofibers is enhanced by a reduced SLN inhibition of SERCA and by an abundant expression of CASQ. Together, these results suggest that horse muscle contractility and susceptibility to exertional rhabdomyolysis are promoted by enhanced SR Ca²⁺ uptake and luminal Ca²⁺ storage.

Continuous Monitoring of the Thermoregulatory Response in Endurance Horses and Trotter Horses During Field Exercise: Baselining for Future Hot Weather Studies

Establishing proper policies regarding the recognition and prevention of equine heat stress becomes increasingly important, especially in the face of global warming. To assist this, a detailed view of the variability of equine thermoregulation during field exercise and recovery is essential. 13 endurance horses and 12 trotter horses were equipped with continuous monitoring devices [gastrointestinal (GI) pill, heartrate (HR) monitor, and global positioning system] and monitored under cool weather conditions during four endurance rides over a total of 80 km (40 km loops) and intense trotter track-based exercise over 1,540 m. Recordings included GI temperature (T c ), speed, HR and pre- and post-exercise blood values. A temperature time profile curve of T c was constructed, and a net area under the curve was calculated using the trapezoidal method. Metabolic heat production and oxygen cost of transport were also calculated in endurance horses. Maximum T c was compared using an independent samples t-test. Endurance horses (mean speed 14.1 ± 1.7 km h-1) reached mean maximum T c (39.0 ± 0.4°C; 2 × 40 km in 8 horses) during exercise at 75% of completion of T c exercise and T c returned to baseline within 60 min into recovery. However, the mean T c was still 38.8 ± 0.4°C at a HR of 60 bpm which currently governs "fit to continue" competition decisions. Trotters (40.0 ± 2.9 km h-1) reached a comparable mean max T c (38.8 ± 0.5°C; 12 horses) always during recovery. In 30% of trotters, T c was still >39°C at the end of recovery (40 ± 32 min). The study shows that horses are individuals and thermoregulation monitoring should reflect this, no matter what type of exercise is performed. Caution is advised when using HR cut-off values to monitor thermal welfare in horses since we have demonstrated how T c can peak quite some time after finishing exercise. These findings have implications for training and management of performance horses to safeguard equine welfare and to maximize performance.

Air Speed to Increase Rate of Cool Out for Horses After Intense Exercise

Cooling out horses is a common practice after intense exercise. Typical cooling procedures include both walking and drenching (often with scraping). The cool out is performed to ensure the horses physiologic responses returned to a baseline range as quickly as possible. The use of water in cool out provides the greatest potential for removing heat from the animals. However, adding air velocities that can increase evaporation rates from the horses can potentially increase the rate of cool out; thereby reducing the time until the horses' physiologic measurements return to baseline. This study measured the rate of cool out for 7 Thoroughbreds, which were run on the track for 1 or 1.5 miles. Animals were provided a combination of walking and drenching in addition to 3 fan treatments no fan, fan directed at lateral side, and fan directed at posterior. Physiologic responses were analyzed using the Multivariate analysis of variance (MANOVA) procedure and while no significant differences were found in the rate of cool out, trends indicated both rectal temperature (P = .10) and heart rate (P = .11) returned to baseline more quickly with the addition of a fan.

Horse Preferences for Insolation, Shade or Mist Curtain in the Paddock under Heat Conditions: Cardiac and Behavioural Response Analysis

The horse's welfare and, consequently, the emotional arousal may be connected with stressful environmental conditions. This study aimed to determine whether horses show behavioural or physiological symptoms of thermal discomfort and if their behaviour and cardiac parameters are related to freely chosen insolated (IS), shaded (SH), or water sprayed (with a mist curtain (MC)) areas in a paddock under heat conditions (29-32 °C, 42.0 ± 1.5% humidity). Twelve adult horses freely moving in the paddock were studied during a 45 min solitary turnout. Six cardiac variables, locomotor, and non-locomotor activities as well as rectal temperature before and after the test were monitored with regard to the area of staying. Horses did not show clear preferences regarding the time spent in IS, SH, and MC, although preferences of particular horses differed considerably. When staying under IS and MC conditions, the horses showed a higher level of relaxation compared to SH. Horses did not exhibit symptoms of thermal discomfort while staying in the sun. Free choice between the three areas differing in environmental conditions could be a crucial factor in maintaining body temperature as well as emotional arousal at similar levels. Thus, the provision of a shade and mist curtain in paddocks seems to be reasonable.

What’s in a warm-up? A preliminary investigation of how European dressage riders and show jumpers warm-up their horses for training and at competition

Equestrian sports such as dressage and show jumping cause physical and physiological stress on the horses’ musculoskeletal structures, which can lead to decreased performance and injury. Warming-up prior to intense exercise can increase utilisation of the aerobic pathway, increase performance and decrease injury risk. Whilst duration of equestrian warm-up regimes has been reported, details of which gaits and skills related tasks, such as jumping and lateral movements, riders elect to use have not been evaluated to date. The purpose of this study was to understand dressage and show jumping riders’ decision-making when warming up at home and prior to a competition. Surveys (dressage: 39 questions; show jumping: 41 questions) were distributed online via social media. Mann Whitney U tests identified significant differences in warming up practice between dressage and show jumping riders. Most riders reported that a warm-up was beneficial for getting the horse ready for work, increasing responsiveness to aids, enhancing suppleness and relaxation, and decreasing injury risk. Both dressage and show jumping riders typically warm-up between 10-20 min. While dressage riders use the walk as their main warm-up gait, show jumpers preferred the trot. Both dressage riders and show jumpers incorporate technical skills in their warm-up such as lateral work, and quick transitions (when riders change gait for only few strides before changing again). Show jumpers include 4-10 jumping efforts, using different fence types. During a competition most dressage and show jumping riders agreed that factors such as perceived stress level of both the horse and rider, crowdedness of the arena, arena footing and size, as well as time allocated by the venue, were important factors that could impact the duration and content of their warm-up routines. Both groups of riders considered horses were sufficiently ‘warmed up’ when they were responsive to the aids and felt supple and relaxed.

The Use of Percutaneous Thermal Sensing Microchips for Body Temperature Measurements in Horses Prior to, during and after Treadmill Exercise

Accurately measuring body temperature in horses will improve the management of horses suffering from or being at risk of developing postrace exertional heat illness. PTSM has the potential for measuring body temperature accurately, safely, rapidly, and noninvasively. This study was undertaken to investigate the relation between the core body temperature and PTSM temperatures prior to, during, and immediately after exercise. The microchips were implanted into the nuchal ligament, the right splenius, gluteal, and pectoral muscles, and these locations were then compared with the central venous temperature, which is considered to be the "gold standard" for assessing core body temperature. The changes in temperature of each implant in the horses were evaluated in each phase (prior to, during, and immediately postexercise) and combining all phases. There were strong positive correlations ranging from 0.82 to 0.94 (p < 0.001) of all the muscle sites with the central venous temperature when combining all the phases. Additionally, during the whole period, PTSM had narrow limits of agreement (LOA) with central venous temperature, which inferred that PTSM is essentially equivalent in measuring horse body temperature. Overall, the pectoral PTSM provided a valid estimation of the core body temperature.

Effects of Pre-Cooling on Thermophysiological Responses in Elite Eventing Horses

Simple Summary

Horses have a high metabolic capacity for exercise, producing a great deal of heat, and have a small surface area for heat loss. Under limited circumstances, the regulation of heat loss (i.e., across the respiratory tract and by the evaporation of sweat) means heat build-up in the body is reduced. Thermoregulation can be assisted by cooling the horses down to safely perform exercise in thermally challenging environments. The present study showed that pre-cooling (i.e., cooling between the warm-up and exercise performance) slightly reduced the rise in rectal, shoulder and rump skin temperatures of ten international eventing horses during moderately intense canter training in moderate environmental conditions. During the canter training, heart rate, sweat rate and sweat composition were unaffected by pre-cooling. The pre-cooling strategy chosen here was cold-water rinsing for a short period of time (~8 min). Considering the limited time and space at equestrian events, such a pre-cooling strategy could easily be implemented. Reducing heat strain by pre-cooling may potentially improve equine welfare during events.

Abstract

In this study, we examined the effects of pre-cooling on thermophysiological responses in horses exercising in moderate environmental conditions (average wet bulb globe temperature: 18.5 ± 3.8 °C). Ten international eventing horses performed moderate intensity canter training on two separate days, and were either pre-cooled with cold-water rinsing (5–9 °C for 8 ± 3 min; cooling) or were not pre-cooled (control). We determined velocity (V), heart rate (HR), rectal temperature (T_re,), shoulder and rump skin temperature (T_shoulder and T_rump), plasma lactate concentration (LA), gross sweat loss (GSL), and local sweat rate (LSR), as well as sweat sodium, chloride and potassium concentrations. The effect of pre-cooling on T_re was dependent on time; after 20 min of exercise the effect was the largest (estimate: 0.990, 95% likelihood confidence intervals (95% CI): 0.987, 0.993) compared to the control condition, resulting in a lower median T_re of 0.3 °C. Skin temperature was also affected by pre-cooling compared to the control condition (T_shoulder: −3.30 °C, 95% CI: −3.739, −2.867; T_rump: −2.31 °C, 95% CI: −2.661, −1.967). V, HR, LA, GSL, LSR and sweat composition were not affected by pre-cooling. In conclusion, pre-cooling by cold-water rinsing could increase the margin for heat storage, allowing a longer exercise time before a critical T_re is reached and, therefore, could potentially improve equine welfare during competition.

Effects of feed removal on thermoregulation and intestinal morphology in pigs recovering from acute hyperthermia

Feed consumption increases body temperature and may delay a return to euthermia and exacerbate intestinal injury following acute hyperthermia recovery in pigs. Therefore, the study objective was to evaluate the effects of feed removal on body temperature and intestinal morphology in pigs exposed to acute hyperthermia and then rapidly cooled. Twenty-four gilts (78.53 ± 5.46 kg) were exposed to thermoneutral (TN; n = 12 pigs; 21.21 ± 0.31 °C; 61.88 ± 6.93% RH) conditions for 6 h, or heat stress (HS; 38.51 ± 0.60 °C; 36.38 ± 3.40% RH) conditions for 3 h followed by a 3-h recovery period of rapid cooling (HSC;n = 12 pigs; TN conditions and cold water dousing). Within each recovery treatment, one-half of the pigs were provided feed ad libitum (AF; n = 6 pigs per recovery treatment) and one-half of the pigs were not provided feed (NF; n = 6 pigs per recovery treatment). Gastrointestinal (TGI), vaginal (TV), and skin (TSK) temperatures and respiration rate (RR) were recorded every 15 min. Pigs were video-recorded to assess feeding and drinking attempts. Immediately following the 6-h thermal stress period, pigs were euthanized, and intestinal samples were collected to assess morphology. During the HS period, Tv, TGI, TSK, and RR were increased (P < 0.01; 1.63, 2.05, 8.32 °C, and 88 breaths per min, respectively) in HSC vs. TN pigs, regardless of feeding treatment. Gastrointestinal temperature was greater (P = 0.03; 0.97 °C) in HSC + AF vs. HSC + NF pigs from 45 to 180 min of the recovery period. During the recovery period, feeding attempts were greater (P = 0.02; 195.38%) in AF vs. NF pigs. No drinking attempt differences were detected with any comparison (P > 0.05). A decrease (P < 0.01) in jejunum and ileum villus height (24.72% and 26.11%, respectively) and villus height-to-crypt depth ratio (24.03% and 25.29%, respectively) was observed in HSC vs. TN pigs, regardless of feeding treatment. Ileum goblet cells were reduced (P = 0.01; 37.87%) in HSC vs. TN pigs, regardless of feeding treatment. In summary, TGI decreased more rapidly following acute hyperthermia when the feed was removed, and this may have implications toward using feed removal as a strategy to promote acute hyperthermia recovery in pigs.

Contrast therapy: Tissue heating and cooling properties within the equine distal limb

BACKGROUND

Rehabilitation of tendon injuries in horses often involves cryotherapy to reduce inflammation and occasionally tissue heating to increase collagen extensibility. The application of alternating cold and hot (ie contrast therapy) is widely used in human physical therapy; however, its utility in equine rehabilitation is largely unknown.

OBJECTIVES

The objectives of this study were to (a) assess if the equipment could achieve therapeutic tissue temperatures (<15 and >40°C) at different tissue depths relative to the digital flexor tendons and (b) evaluate the time-temperature profiles during serial heating and cooling cycles using a contrast therapy device.

STUDY DESIGN

In vivo experiment.

METHODS

In 4 adult horses with normal forelimb digital flexor tendons, fine-wire temperature probes were placed superficially on the skin and implanted subcutaneously, deep to the superficial digital flexor tendon (SDFT) and deep to the deep digital flexor tendon (DDFT). Temperatures were recorded over three complete thermal (hot-cold) cycles. Minimum and maximum temperatures were recorded and the rate of temperature changes and the areas underneath the time-temperature curves (ie thermal load) were calculated.

RESULTS

Minimum and maximum tissue temperatures (°C) included: superficial skin [12.6 ± 1.0; 42.4 ± 2.4], subcutaneous tissues [14.1 ± 0.8; 42.3 ± 2.2], deep to the SDFT [15.6 ± 0.8; 41.7 ± 2.6] and deep to DDFT [25.1 ± 2.0; 38.0 ± 3.5]. An initial rapid rate of tissue temperature change between 3.2 and 4.3°C/min occurred within tissues to the depth of the DDFT. Tissue thermal loads during heating ranged from 255 to 607°C*second and from 309 to 780°C*second during tissue cooling, with the lower values noted deep to the DDFT.

MAIN LIMITATIONS

Unknown clinical efficacy in diseased tissues.

CONCLUSIONS

The applied contrast therapy was consistently able to induce cooling and heating of tissues to the depth of the DDFT.

Validation of exercise-response genes in skeletal muscle cells of Thoroughbred racing horses

Objective

To understand the athletic characteristics of Thoroughbreds, high-throughput analysis has been conducted using horse muscle tissue. However, an in vitro system has been lacking for studying and validating genes from in silico data. The aim of this study is to validate genes from differentially expressed genes (DEGs) of our previous RNA-sequencing data in vitro. Also, we investigated the effects of exercise-induced stress including heat, oxidative, hypoxic and cortisol stress on horse skeletal muscle derived cells with the top six upregulated genes of DEGs.

Methods

Enriched pathway analysis was conducted using the Database for Annotation, Visualization, and Integrated Discovery (DAVID) tool with upregulated genes in horse skeletal muscle tissue after exercise. Among the candidates, the top six genes were analysed through geneMANIA to investigate gene networks. Muscle cells derived from neonatal horse skeletal tissue were maintained and subjected to exercise-related stressors. Transcriptional changes in the top six genes followed by stressors were investigated using quantitative reverse transcription-polymerase chain reaction (qRT-PCR).

Results

The inflammation response pathway was the most commonly upregulated pathway after horse exercise. Under non-cytotoxic conditions of exercise-related stressors, the transcriptional response of the top six genes was different among types of stress. Oxidative stress yielded the most similar expression pattern to DEGs.

Conclusion

Our results indicate that transcriptional change after horse exercise in skeletal muscle tissue strongly relates to stress response. The qRT-PCR results showed that stressors contribute differently to the transcriptional regulation. These results would be valuable information to understand horse exercise in the stress aspect.

An application of temperature mapping of horse's back for leisure horse-rider-matching

Leisure riding is a popular way of using horses however, unlike sport or racing horses, those are mostly not associated with one rider with high skills. Constant overload of equine musculoskeletal system causes pathologies, which are affecting horse mobility and decreases the horse-rider communication. The aim was to propose the new scoring system of thermograph analysis as an aspect of differences in heat distributions on horseback before and after leisure ridings. The study was conducted on sixteen Polish warmblood horses, scanned with a non-contact thermographic camera. Heat pattern of the thoracolumbar area was evaluated on thermograms taken before and after exercise. The criteria with point values for horse-rider-matching were created: heat points on the dorsal midline of saddle-back contact area and degree of muscle unit overload. The results of thermograph analysis were compared with the results of a questionnaire on horse-rider communication during riding in order to estimate the relevance of matching. The maximum score was obtained in 38.3% and 39.8% of combinations based on the thermograph analysis and questionnaire, respectively. Results of both scoring systems were strongly positive correlated (r = .937), demonstrating high sensitivity (61.72%) and specificity (90.23%) of the matching. The horse-rider matching may improve horse comfort during leisure type of work.

The effect of heat stress on frame switch splicing of X-box binding protein 1 gene in horse

Objective

Among stress responses, the unfolded protein response (UPR) is a well-known mechanism related to endoplasmic reticulum (ER) stress. ER stress is induced by a variety of external and environmental factors such as starvation, ischemia, hypoxia, oxidative stress, and heat stress. Inositol requiring enzyme 1α (IRE1α)-X-box protein 1 (XBP1) is the most conserved pathway involved in the UPR and is the main component that mediates IRE1α signalling to downstream ER-associated degradation (ERAD)- or UPR-related genes. XBP1 is a transcription factor synthesised via a novel mechanism called ‘frame switch splicing’, and this process has not yet been studied in the horse XBP1 gene. Therefore, the aim of this study was to confirm the frame switch splicing of horse XBP1 and characterise its dynamics using Thoroughbred muscle cells exposed to heat stress.

Methods

Primary horse muscle cells were used to investigate heat stress-induced frame switch splicing of horse XBP1. Frame switch splicing was confirmed by sequencing analysis. XBP1 amino acid sequences and promoter sequences of various species were aligned to confirm the sequence homology and to find conserved cis-acting elements, respectively. The expression of the potential XBP1 downstream genes were analysed by quantitative real-time polymerase chain reaction.

Results

We confirmed that splicing of horse XBP1 mRNA was affected by the duration of thermal stress. Twenty-six nucleotides in the mRNA of XBP1 were deleted after heat stress. The protein sequence and the cis-regulatory elements on the promoter of horse XBP1 are highly conserved among the mammals. Induction of putative downstream genes of horse XBP1 was dependent on the duration of heat stress. We confirmed that both the mechanisms of XBP1 frame switch splicing and various binding elements found in downstream gene promoters are highly evolutionarily conserved.

Conclusion

The frame switch splicing of horse XBP1 and its dynamics were highly conserved among species. These results facilitate studies of ER-stress in horse.