Comparison of temperature readings from a percutaneous thermal sensing microchip with temperature readings from a digital rectal thermometer in equids

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.

Agreement of Temperatures Measured Using a Non-Contact Infrared Thermometer With a Rectal Digital Thermometer in Horses

Evaluating the body temperature of horses is an essential tool for monitoring horse health and biosecurity in groups of horses. Temperatures of horses and foals are determined most often using rectal thermometry. Rectal thermometry has limitations that include safety considerations for horses and humans. Thus, we investigated the agreement between a noncontact infrared thermometer (NCIT) and a rectal digital thermometer in 142 horses and 34 foals. For each horse and foal, measurements using the NCIT were collected from the forehead (n = 2) or neck (n = 1) and with a rectal digital thermometer (n = 1). Although the NCIT demonstrated good reliability (i.e. repeatability of measurements), a large negative bias (nearly 2°F (-16.7°C) in adult horses and >3°F (-16.1°C) in foals) was observed between readings from the NCIT and the rectal thermometer in healthy horses. Although horses with febrile illness were not included in the study, our results indicate that the large and inconsistent bias observed with the NCIT indicates that these devices will not be a suitable substitute for rectal thermometry for obtaining valid estimates of core body temperature in horses.

The use of percutaneous thermal sensing microchips for non-invasive measurement of body temperature in foals during summer seasons in a subtropical region

Continuous accurate attainment of the body temperature of foals is important to detect early stages of severe heat stress or fever due to a systemic illness. Among a number of methods to measure body temperature, measuring rectal temperature with a digital thermometer is most frequently used due to being relatively fast and simple method. It is also comparatively accurate and correlates well with the core body temperature. However, this method requires restraining the foal for a few seconds to obtain the temperature, and it can be dangerous for the handling person. Percutaneous thermal sensing microchips (PTSMs) are a means of monitoring the body temperature of horses, which offers a non-invasive, hygienic, quick, and accurate way to measure body temperature and provide an identification number for each individual, once it is implanted. This study tested the hypothesis that PTSM has a strong relationship with a conventional body temperature measurement, i.e., measuring rectal temperature with a digital thermometer of foals during summer seasons. Thirty-two foals in three consecutive foaling seasons (2018, 2019, and 2020 season) were implanted a PTSM into the right pectoral muscle, the right splenius muscle, the right gluteal muscle, and the nuchal ligament as early as two weeks after birth. The four PTSM temperatures, rectal temperature, and climate conditions (air temperature, relative humidity, and wet-bulb globe temperature) were obtained simultaneously during the three summer seasons and paired for comparison analysis. Among the PTSM temperatures, the pectoral muscle had the highest correlation and the least differences with rectal temperature. Using PTSM was safe, easy, and reliable for attaining body temperature in foals.

Eye surface infrared thermography usefulness as a noninvasive method of measuring stress response in sheep during shearing: Correlations with serum cortisol and rectal temperature values

During shearing, animals' welfare is adversely affected and acute stress occurs. Once animal perceives a threat, it develops behavioral, autonomic, endocrine or immune responses to maintain homeostasis. This study aimed to investigate the usefulness of eye temperature assessment by infrared thermography (IRT) to evaluate acute stress response in sheep undergoing a shearing procedure. From each animal, blood sampling, rectal and eye temperature assessment were performed before shearing (T_PRE), 5 (T_POST5) and 60 (T_POST60) minutes after the end of shearing procedure. On blood samples the serum cortisol concentrations were evaluated. Rectal temperature (T_RECTAL) was measured using a digital thermometer. Thermographic acquisitions of eye temperature were performed from the eye total area (T_EYE) and from three regions of interest (lateral canthus, T_ROI-1; central cornea, T_ROI-2; medial canthus, T_ROI-3). One-way analysis of variance showed a significant increase of serum cortisol concentration, T_RECTAL, T_EYE and T_ROI-3 (p < 0.001). Serum cortisol was positively correlated with T_RECTAL and T_ROI-3 at T_POST5 and T_POST60. T_RECTAL resulted positively correlated with T_ROI-3 at T_PRE, T_POST5 and T_POST60. Agreement between T_RECTAL and each eye temperature considered (T_EYE, T_ROI-1, T_ROI-2, T_ROI-3) has been shown by Bland-Altman plots at each time point of monitoring period. The findings obtained in the current survey suggest that the medial canthus is the most suitable region for eye temperature measurement to asses stress response in animals. Moreover, this study highlighted the usefulness of IRT as an immediate and non-invasive physiological measure to assess stress response in sheep.

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.

Thermographic ocular temperature correlated with rectal temperature in cats

Body temperature reflects the animal health and/or disease conditions. During clinical examination, temperature measurement is a basic step in veterinary medicine. The conventional method used is the rectal thermometry, particularly stressful in some subjects, especially for cats. A less stressful alternative method, such as infrared thermal imaging camera, is used in various fields of medicine for diagnosis, prognosis and correct therapeutic approaches. To evaluate the usefulness of infrared thermal imaging for the assessment of ocular temperature, twenty cats of different breeds (European, Siamese and Persian, 4-6 years old, mean body weight 4.3 ± 0.30 Kg) were enrolled in the study. In order to evaluate the applicability of the ocular temperature assessment through thermal imaging as a tool for measuring the animal's body temperature, the obtained values were compared with the rectal temperature values recorded in each cat by means of a digital thermo-camera. There were no differences between left and right eye; and a difference of about 1.19 °C between the ocular and rectal temperature value was recorded (p < 0.0001). Rectal and ocular temperatures were positively correlated (p < 0.0001; r = 0.93). In conclusion, we show that ocular temperature is an alternative method for body temperature measurement that can be used in clinical evaluation of cats, especially in cases where rectal temperature recording is not possible.

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.

Effect of the Depth of Insertion of the Thermometer on the Rectal Temperature of Donkeys During the Hot-Dry Season in a Tropical Savannah

The objective of the present study was to evaluate the effect of the depth of insertion and environmental parameters on the rectal temperature (RT) in donkeys during the hot-dry season in a tropical savannah zone of Nigeria. The experimental subjects were comprised of thirty donkeys divided into three groups based on age: group I, 10 foals (40.67 ± 2.20 kg; 1.50 ± 0.02 months); group II, 10 yearlings (91.53 ± 0.54 kg; 1.51 ± 0.01 years); and group III, 10 adults (140 ± 0.71 kg; 8.03 ± 0.06 years). Each group was divided into 5 male and 5 female donkeys. Measurements of the RT were recorded with a digital thermometer probe (model HI935007, Hanna Instruments), which was inserted into the rectum at varying depths of 3.5, 7, 10.5, and 14 cm in the same animal in each group. There was a gradual increase in the RT in donkeys as the depth of insertion was increased from 3.5 cm (36.60°C) to 14 cm (38.40°C). Data obtained from the study were subjected to repeated-measures analysis of variance, followed by Tukey's post-hoc test to compare mean values between different depths of RT measurements. Overall, there was a variation in the RT by the depth of insertion with the shallow depth of 3.5 cm having a lower RT than the depths of 7, 10.5, and 14 cm. The variation of the RT observed in donkeys showed that there is need to standardize the probe-insertion depth in veterinary clinical practice for accurate measurement of the RT in donkeys in the Northern Guinea savannah zone of Nigeria.

Effect of a bandage or tendon boot on skin temperature of the metacarpus at rest and after exercise in horses

OBJECTIVE

To determine the skin temperature of the metacarpus in horses associated with the use of bandages and tendon boots, compared with the bare limb, at rest and after 20 minutes of lunging.

ANIMALS

10 adult horses.

PROCEDURES

Skin temperature on the bare metacarpus of both forelimbs was measured at rest and after lunging. Subsequently, a bandage was applied to the left metacarpus and a tendon boot to the right metacarpus and skin temperature was measured at rest and after lunging. Skin temperature was measured with fixed sensors and thermographically.

RESULTS

Mean ± SD skin temperatures of the bare metacarpi were 14.1 ± 2.4°C (left) and 14.1 ± 3.4°C (right) at rest, and 14.4 ± 1.8°C (left) and 13.6 ± 2.6°C (right) after exercise. Skin temperatures under the bandage were 15.3 ± 1.6°C at rest and 24.8 ± 3.6°C after exercise. Skin temperatures under the tendon boot were 15.3 ± 2.6°C at rest and 20.6 ± 2.9°C after exercise. Skin temperatures under the bandage and tendon boot were significantly higher after exercise than at rest. Skin temperatures at rest were not significantly different with a bare limb, bandage, or tendon boot.

CONCLUSIONS AND CLINICAL RELEVANCE

Skin temperature of the metacarpus in horses increased significantly during exercise but not at rest when a bandage or tendon boot was used. The authors speculate that both a bandage and a tendon boot accelerate the warm up phase of exercise. Further research should focus on the effects of warm up and maximum exercise on the temperature of other anatomic structures such as tendons.

Assessment of the use of temperature-sensitive microchips to determine core body temperature in goats

Body temperature was measured at five different body sites (retroperitoneum, groin, semimembranosus muscle, flank and shoulder) using temperature-sensitive microchips implanted in five female goats, and compared with the core body and rectal temperatures. Body temperature was measured while the goats were kept in different ambient temperatures, with and without radiant heat, as well as during a fever induced experimentally by injection of bacterial lipopolysaccharide. Bland-Altman limit of agreement analysis was used to compare the temperature measurements at the different body sites during the different interventions. Temperatures measured by the microchip implanted in the retroperitoneum showed the closest agreement (mean 0.2 °C lower) with core and rectal temperatures during all interventions, whereas temperatures measured by the microchips implanted in the groin, muscle, flank and shoulder differed from core body temperature by up to 3.5 °C during the various interventions.