Thermoregulatory capacity of the Thoroughbred racehorse and its relationship to the pathogenesis of exertional heat illness

Brownlow, M. A.; Mizzi, J. X.

doi:10.1111/eve.13433

Cited by 11 publications

(23 citation statements)

References 40 publications

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“…The identification of ongoing hyperthermia during recovery is essential information with respect to equine welfare and emphasizes the need for extended continuous monitoring post-exercise. Our findings may explain personal anecdotal evidence expressed by trotter trainers noticing that some horses show discomfort the day after an otherwise uneventful competition day ( Courouce et al, 2002 ; Richard et al, 2010 ; Bertuglia et al, 2014 ) due to unrecognized post-racing hyperthermia ( McConaghy et al, 2002 ; Brownlow and Mizzi, 2020 , 2021 ). The current findings also underline that the habit of withholding water prior to racing events is not an ideal practice.…”

Section: Discussionmentioning

confidence: 63%

“…Exertional heat illness (EHI) in horses is characterized by severe central nervous system dysfunction, such as physical collapse, and has been described in detail ( Brownlow et al, 2016 ; Brownlow and Mizzi, 2020 ). Recently, a Japanese study identified a wet-bulb globe temperature (WBGT) index above 28°C to be responsible for a 28.5% higher risk for development of EHI when compared to the index below 20°C ( Takahashi and Takahashi, 2020 ).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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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 (Tc), speed, HR and pre- and post-exercise blood values. A temperature time profile curve of Tc 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 Tc was compared using an independent samples t-test. Endurance horses (mean speed 14.1 ± 1.7 km h–1) reached mean maximum Tc (39.0 ± 0.4°C; 2 × 40 km in 8 horses) during exercise at 75% of completion of Tc exercise and Tc returned to baseline within 60 min into recovery. However, the mean Tc 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 Tc (38.8 ± 0.5°C; 12 horses) always during recovery. In 30% of trotters, Tc 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 Tc 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.

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Section: Discussionmentioning

confidence: 63%

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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“…The MH produced during exercise needs to be dissipated from the horse to the surrounding environment through four main pathways, namely, radiation, conduction, convection, and evaporation, the last being the most essential and pivotal pathway in horses ( 23 , 48 , 53 – 56 ). Evaporation from the body surface is mainly achieved by increased blood flow, cutaneous vasodilation followed by evaporation of sweat from the skin (70–85% of the MH load) ( 25 , 48 , 54 , 56 – 59 ). Heat loss by evaporation can be enhanced by cooling techniques ( 35 , 40 , 43 ).…”

Section: Introductionmentioning

confidence: 99%

“…Monitoring T sk simultaneously with T c using the GI temperature pill during field exercise has not yet been investigated. The relationship between T sk and T c is not well understood due to physiological, endocrine, or vasomotor influences on both temperatures ( 25 , 56 , 59 ). Some studies have tried to correlate both T c and T sk ( 39 – 42 ).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2022

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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 (Tsk) coincident with core temperature (Tc) has not previously been investigated in horses exercising in the field. We investigated the suitability of monitoring surface Tsk as a metric of the thermoregulatory response, and simultaneously investigated its relationship with Tc using gastrointestinal (GI) temperature. We evaluated Tsk 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. Tsk and Tc 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 Tsk over time (°C × minutes) using the trapezoidal method. The relationship between Tsk and Tc was assessed using scatterplots, paired t-test or generalized linear model ANOVA (delta Tsk) (n = 8). Ambient temperature ranged from 6.7°C to 18.4°C. No relationship was found between Tsk and Tc profiles during exercise and recovery periods, and no significant difference between delta Tsk results was detected when comparing exercise and rest. However, time to maximum Tsk (67 min) was significantly reduced compared to Tc (139 min) (p = 0.0004) with a significantly lesser maximum Tsk (30.3°C) than Tc (39°C) (p = 0.0002) during exercise. Net AUC Tsk was 1,164 ± 1,448 and −305 ± 388°C × minutes during periods of exercise and recovery, respectively. We conclude that Tsk monitoring does not provide a reliable proxy for the thermoregulatory response and horse welfare, most probably because many factors can modulate Tsk without directly affecting Tc. Those factors, such as weather conditions, applicable to all field studies can influence the results of Tsk in endurance horses. The study also reveals important inter-individual differences in Tsk and Tc time profiles, emphasizing the importance of an individualized model of temperature monitoring.

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“…1 Although only recently described in detail in racing thoroughbreds, [1][2][3][4] Brownlow has provided detailed clinical descriptions of the characteristics of this syndrome and termed it exertional heat illness (EHI) after a similar condition in human athletes. 2,[5][6][7] There is, however, minimal literature on the rates of occurrence and environmental risk factors for this syndrome. [1][2][3][4] Thoroughbred racing in temperate eastern Australia occurs over relatively short distances and durations.…”

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confidence: 99%

An investigation into environmental variables influencing post‐race exertional heat illness in thoroughbred racehorses in temperate eastern Australia

Brownlow

Brotherhood

2021

Aust Veterinary J

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Exertional heat illness (EHI) is a syndrome that occurs when metabolic heat production from muscular contraction exceeds the rate at which it can be dissipated. Core body temperature rises to critical levels, causing hyperthermia and central nervous system dysfunction. Best practice for the prevention of EHI centres around early detection, rapid response and aggressive cooling. Advance planning enables risk mitigation measures. The more that is known about EHI in horses, the better prepared those in the positions of responsibility can be to anticipate events in which the risk of EHI may be elevated. This prospective, observational study investigated environmental risk factors associated with the occurrence of EHI. From 2014 to 2018, the number of horses exhibiting the symptoms of post-race EHI was recorded at 73 convenience sampled race meetings. Of the 4809 starters, the signs of EHI were recorded for 457. Thermal environmental data were measured and included ambient temperature, radiant heat, vapor pressure (humidity) and wind speed (WS). Mixed linear regression models were computed to assess the associations between the occurrence and incidence of post-race EHI and the four thermal environmental variables. The analysis showed that vapor pressure and WS had the largest effects on the occurrence of post-race EHI. The major limitations were that the race meetings selected were convenience sampled according to attendance by the first author and individual horse data were not available. EHI is influenced by a complex interaction of independently acting environmental variables, but warm, windless, humid days are most likely to result in the cases of EHI.Keywords ambient temperature; environmental variables; exertional heat illness; radiant heat; thoroughbred racehorses; vapour pressure; wet-bulb globe temperature; wind speed Abbreviations DB, Tdb ( C), dry-bulb air temperature; EHI, exertional heat illness; EHIRS, exertional heat illness race status (i.e. did at least one horse show post-race symptoms of EHI? [yes/no]); MRT ( C), mean radiant temperature; PEHI, percentage of horses showing the signs of post-race EHI; Tg ( C), globe temperature; Twb ( C), wet-bulb temperature; VP, vapour pressure (also referred to as absolute humidity, kPa); WBGT ( C), wet-bulb globe temperature; WS, wind speed (m/s)

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Thermoregulatory capacity of the Thoroughbred racehorse and its relationship to the pathogenesis of exertional heat illness

Cited by 11 publications

References 40 publications

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

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

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

An investigation into environmental variables influencing post‐race exertional heat illness in thoroughbred racehorses in temperate eastern Australia

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