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.

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.

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.

New Insights into the Management of an EHV-1 (Equine Hospital) Outbreak.

In May 2018, Wolvega Equine Hospital (WEH) experienced an EHV-1 outbreak. This outbreak caused significant economic losses and negative publicity for the hospital. How should hospitals prepare themselves for these outbreaks and prevent shedding of the virus on multiple neighboring premises? The hospital transformed most of its activities into mobile practice and the entire infected hospital population was moved to a separate remote location. The hospital was cleaned and disinfected according to the latest recommendations before reopening. Four neighboring professional equine businesses and three privately owned premises were affected by the spread of the virus from the hospital population and initiated quarantine restrictions. Equine hospitals should prepare themselves for EHV-1 outbreaks as the intake of the virus cannot be prevented. A management protocol should include public information protocols, swift client information and quarantine measures that ensure quick containment of the outbreak. Timely reopening of the hospital can be achieved by rehousing the contaminated population. It should also include good regulations with clients and a properly carried out release protocol. Equine sports organizations should establish sufficient vaccination coverage in order to decrease the frequency of EHV-1 outbreaks.

Plasma serotonin in horses undergoing surgery for small intestinal colic.

This study compared serotonin concentrations in platelet poor plasma (PPP) from healthy horses and horses with surgical small intestinal (SI) colic, and evaluated their association with postoperative ileus, strangulation and non-survival. Plasma samples (with EDTA) from 33 horses with surgical SI colic were collected at several pre- and post-operative time points. Serotonin concentrations were determined using liquid-chromatography tandem mass spectrometry. Results were compared with those for 24 healthy control animals. The serotonin concentrations in PPP were significantly lower (P < 0.01) in pre- and post-operative samples from surgical SI colic horses compared to controls. However, no association with postoperative ileus or non-survival could be demonstrated at any time point. In this clinical study, plasma serotonin was not a suitable prognostic factor in horses with SI surgical colic.

Sérotonine plasmatique chez des chevaux subissant une chirurgie pour des coliques du petit intestin. Cette étude a comparé les concentrations de sérotonine dans le plasma faible en plaquettes (PFP) de chevaux en santé et de chevaux atteints de coliques chirurgicales du petit intestin et a évalué leur association avec l'occlusion intestinale postopératoire, la strangulation et la non-survie. Des échantillons de plasma (avec EDTA) ont été prélevés auprès de 33 chevaux atteints de coliques du petit intestin à plusieurs moments préopératoires et postopératoires. Les concentrations de sérotonine ont été déterminées à l'aide d'un spectromètre de masse LC-ESI-MS/MS. Les résultats ont été comparés avec ceux de 24 animaux témoins en santé. Les concentrations de sérotonine du PFP étaient significativement inférieures (P < 0,01) dans les échantillons préopératoires et postopératoires provenant des chevaux atteints de coliques du petit intestin comparativement aux animaux témoins. Cependant, aucune association avec l'occlusion intestinale postopératoire ou la non-survie n'a pu être démontrée à aucun moment. Dans cette étude clinique, la sérotonine plasmatique ne s'est pas avéré un facteur de pronostic approprié chez les chevaux atteints de coliques chirurgicales du petit intestin.(Traduit par Isabelle Vallières).

Comparative analysis of serotonin in equine plasma with liquid chromatography--tandem mass spectrometry and enzyme-linked immunosorbent assay.

Serotonin is regularly measured in equine platelet-poor plasma in research settings. However, reported reference values vary between studies, partially because plasma serotonin concentrations are very low and a reliable and affordable detection method is lacking. A simple, rapid, and sensitive method for serotonin determination in equine platelet-poor plasma using liquid chromatography--tandem mass spectrometry (LC-MS/MS) was developed and validated. Results of a commercially available enzyme-linked immunosorbent assay (ELISA) were compared to the LC-MS/MS results, in order to validate a test more suitable for use in a clinical situation. For LC-MS/MS, 500 µl of plasma was required, and deuterated serotonin was used as an internal standard. The sample preparation was based upon a simple liquid extraction into ethyl acetate. Chromatographic separation was performed with an acetic acid--acetonitrile mobile phase gradient elution. Linearity was demonstrated between 3 ng/ml and 100 ng/ml. A limit of quantification of 3 ng/ml was achieved, corresponding to a limit of detection of 0.10 ng/ml. Comparison of LC-MS/MS and ELISA with Passing-Bablok regression and Bland--Altman plotting showed a poor agreement between the 2 methods, with an increasing difference within the higher range of measurements. Caution is needed when extrapolating results from sources using different analytical techniques.